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Solid State Amplifiers => Amplifier Discussion => Topic started by: EDWARDEFFECT1 on July 22, 2013, 02:48:49 PM

Title: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on July 22, 2013, 02:48:49 PM
i have a polytone taurus elite amp that has low volume on all 3 channels.the speaker test good with a 9v battery test. the output transistors test good.all parts on the board attached to the power transformer test good.solder joints look good.need a schematic if anyone has one available.channel 3 volume control was broken. i need to relace it.i believe it measures 250k.on the channel 1 board i checked the diodes ,capacitors and resistors and they test good.they are located behind the pilot light.any help appreciated....ed!!
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on July 22, 2013, 04:31:07 PM
just did some searching on the net and found out this is a keyboard amp.i was trying a guitar thru the amp and the volume is low.i'm sure it will be louder running a line signal thru it ,but i'm sure it won't be 140 watt loud as listed in the broshure on the amp...still can't find a schematic anywhere?
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: Roly on July 23, 2013, 03:58:24 PM
I found these, the first may be some sort of general help;

http://www.murchmusic.com/polytoneserviceinfo.htm (http://www.murchmusic.com/polytoneserviceinfo.htm)

...but I also found a number of comments from very dissatisfied customers - brand new amp with fault, won't repair, won't send circuit, etc.  This story alone suggests that asking Polytone direct will be a waste of time.  With this sort of company techs need to do tracings of every one of their amps they encounter and publish them free on the web.

Crisp piccies seem in order.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on July 23, 2013, 04:01:17 PM
hooked up a keyboard to the amp and it is low in volume on all 3 channels with the volume and master volume controls full up.if i let it run for about 3 or 4 minutes it starts making a clicking sound that is in perfect rhytum like a metronome. sometimes i can hold a key down and the volume will jump up to full volume for a split second if i pick the right key to hold.i have all the reverb and modulation knobs turned all the way off.i am getting close to finding the problem.may be a heat issue ic,transistor or something. will have to try the pinkie test.  thanks....ed!
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on July 23, 2013, 04:04:28 PM
polytone has not answered me back about my request for a schematic.i see a polytone taurus 2 channel amp schematic for $20.00 which is different than the polytone taurus elite keyboard amp i have.guess i can't even buy one on the net...i'll check your site out you sent... thanks Roly.....ed!
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: Enzo on July 23, 2013, 06:34:20 PM
Try calling them on the phone.   Emails can be ignored, at least talking to someone, they will tell you outright that they will or will not send schematics.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: Roly on July 24, 2013, 03:53:01 AM
I won't be holding my breath.

http://www.gearslutz.com/board/geekslutz-forum/580867-source-polytone-amp-schematics.html
Quote
They have the absolute worst customer service I have ever dealt with. my Polytone mini brute ii was purchased brand new and had immediate problems right out of the box. I contacted Polytone to see if they can fix it. The lady there (Diana) flat out said no we are way too busy and refered me to a place in NJ (Danny's amp repair). I then asked if I can please have a schematic so I can have one on hand cause I am going to search out a local tech. she was very difficult about giving me one but finally took my fax and email. 4 days later I still have no schematic. I left them 3 polite messages in the mean time. I have not heard a peep back. Really upsetting. I purchased the amp new (came without a single document, and no warrenty info), they will not repair it, and they don't even have the courtiosy return my call or fax over a piece of paper. It's almost like she enjoys making my life difficult.

{this has to be one of the worst non-service stories I've ever heard - they wouldn't back up a brand new amp?}


Meh.  Don't sweat the circuit; get in there and have a look and see what you've got (post pix), then we'll just do a bit of technishing and fix it, eh?  Five'll get ya ten it's just a blown output stage.

Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on July 24, 2013, 04:16:46 PM
i have already called and i had a friend call and he told them to call him as he wanted to buy from them.all you get is an answering machine.guess what no call back to either of us.maybe i'll have someone else call as three times might be the charm.ha! ha!...i think Roly has tried this before.guess i'm s.o.l.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: Roly on July 24, 2013, 11:33:08 PM
An answering machine is not a sign of a customer-focused dynamic company giving the player's needs a high priority.  Why am I not surprised?

Nah; "You never find just one roach in a kitchen".  After reading a number of negative posts with no balancing or offsetting posts, you get the general impression.  I mean, have a look at this (http://www.accordion-o-rama.com/TAURUS%20ELITE.htm) and ask yourself if this is a company you would be keen to do business with.

On one hand I'd say persist with them, expecting nothing, just to prove the point; but on the other, time to dust off the camera and multimeter, and trace out the circuit...

Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on July 26, 2013, 05:16:47 PM
found a cracked solder joint on an electrolytic resoldered and got rid of the clicking sound.it was on the master volume board .047uf i believe.i noticed all three of the preamp boards have the same circuit board with different configurations.just have low power now.i have a trace that goes to an opto-isolator that has been cut.not sure if it came from the factory or it is part of my problem.without a schematic who knows! if i take a reading with my meter on dc from the transistor case to ground is get -.0032 on one side and .0012 on the other.not sure ,but shouldn't it be +15vdc on the npn transistor and - 15vdc on the pnp.guessing i have a voltage problem in the 15vdc circuit.any thoughts appreciated....ed
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: DrGonz78 on July 27, 2013, 04:11:25 AM
Why not add some pics to this thread. For one I would like to see a pic of the power supply circuit. It helps to have these pics of the amp out here online for all to see later down the road too. I think we need to start at the power supply and work out the voltage readings through the amp. Lets figure out where on the circuit they create the lower 15v rails (i.e. dropping resistors).
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: Roly on July 27, 2013, 08:43:54 AM
Quote from: EDWARDEFFECT1
sometimes i can hold a key down and the volume will jump up to full volume for a split second
...
a heat issue ic,transistor or something

That sounds more like an intermittent contact/connection.  Solid state devices don't just fix themselves if presented with the right frequency.

Method 1 is is guess, randomly replace parts, and get nowhere.

Method 2 is to methodically and logically trace signals and voltages until the cause of the problem is located, then fix it.

Polytone Taurus Elite, front panel;

(http://www.cavallimusica.com/pages/chitarre/immagini/_Ampli_chitarra/Ampli%20chitarra%20Politone%20taurus%20elite/Ampli-chitarra-Politone-taurus-elite-head.jpg)

A couple of tests that suggest themselves are to take a signal from he Preamp Out socket to another amp and see if that sounds normal.

Similarly to take the Fx Send of another amp and inject it into Effects Loop Input and see if a clean high power output can be obtained.  That way we will have some sort of idea when end of the amp we should be looking at, preamp or main amp.  Also the old trick of linking Fx Out and In with a known good lead.

I must comment that I don't find the control layout on this amp very intuitive.

Inside, the first port of call should be the power supply to confirm voltages for the preamps and output stage (and a cap with a value of 0.047uF is very unlikely to be an electrolytic).
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: J M Fahey on July 27, 2013, 08:17:35 PM
Please do all this and post results:
1) put >master< volume on 10.
2) in all channels, put all 3 tone controls in >5< , dark/bright switch on center position, volume on >0<
3) put all reverb controls, both channel and master, on >0<
4) put all >modulator< controls on >0< , clicking >speed< off.
5) put a known good plug/plug cable from Effects >out< to >in< , and set both >gain< controls to >5< .
6) inject 200mV RMS @ 400Hz to 1KHz in channel 1 input.
Scope speaker output and raise >volume 1< slowly until speaker output starts clipping, then lower a little until it *almost* cleans up.
Measure and post AC voltage here.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on July 28, 2013, 07:35:58 PM
drgonz78, i took pictures for you and the rest of the guys on the site as i had the whole preamp master volume assembly out and the output power transformer.i have tried to upload photos before and had problems. i'll try to send them if someone can dirrect me in what to do...thanks. i have the pictures on my computer to forward what next....ed!!

i took 13 pictures!
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on July 28, 2013, 08:03:33 PM
i just tried loading the photos to photobucket as that is what i was told to do last time. i still could log in ,but had no luck uploading the pictures...help!!

i'll put the amp back together once i upload the pictures and try to get to my signal generator and scope and see if i can do what you have requested JM.......ed!
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: DrGonz78 on July 29, 2013, 02:01:39 AM
You can also rely on fileden.com for upload of these files, as it is a simple to use file server site.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on July 29, 2013, 06:02:43 AM
i have been trying for 4 1/2 hours to load the photos i took.i tried to goto fileden.com and i can't even connect with the site to start an account. i also tried photobucket with no results.it's 5:58am and i'm going to bed. i'll try again in the morning.maybe it isn't yahoo friendly.maybe its because the photos are in documents and settiongs administrator.i really don't know. it should take under a minute to do this and it is really a hair puller. anyone else have any ideas on uploading these ,so they can be viewed by others that the pictures may help. i did see one fellow asking where a wire went on the same amp. my picture might show him. it was an older post ,but who knows he might still need the info...ed!
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: DrGonz78 on July 29, 2013, 06:18:10 AM
yeah dude go sleep at that point!! I hate when crap like that happens, as it is like the World Wide Web is against you!! Don't worry man it all works in the end... or so I was told too  :trouble
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on July 30, 2013, 03:03:41 AM
lets see if this works! i cut and pasted the browser into this post....ed!


http://s1093.photobucket.com/user/edwardeffect1/library/#/user/edwardeffect1/library/POLYTONE%20TAURUS%20ELITE?sort=3&page=1&_suid=1375167601484007348028784194593

going to put the amp back together today to do more testing.thanks for your patience.it's 3:15am and i woke up thinking how to make this post so eveyone could view the pictures i took.i do my best thinking in my sleep.when i try to learn a guitar song i play it before i go to bed.then i end up playing the song back in my head during sleeping.it works...ed
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: DrGonz78 on July 30, 2013, 04:28:06 AM
Well it is good to have the pictures online so everyone has an idea to see the Rat's nest we are working on here. I love Polytone amps but looking inside of them it is always a wonder how they sound so good... I follow all the advice given thus far from Juan and others... However looking at the pics I have to question what caused the browning of the circuit board here... Did you inspect the traces on this part and test the mylar film cap for any damage?

Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: Roly on July 30, 2013, 05:52:32 AM
Can you find good main power rails, like +/-40 volts?

Can you find good preamp supply rails, like +/-15 volts?

Have you tried injecting a signal into Fx Return?  What happened?
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on July 30, 2013, 12:47:38 PM
tried a cascio keyboard thru the effects return.amp has the same low volume.about the same as going thru the input of any of the three channels.the brown in the picture of the mylar cap is solder rosin. the cap climbs to .809k in circuit..it probably is good,it probably is reacting to other components in the circuit.without a print who knows.as for the rail voltages i don't know how i can take any readings off the transfromer board side of the circuit.it has 2 short wired connectors (moldex connectors) to get any voltage readings off that area i would need to have  2 or 3 ft jumper connectors with modex connectors. i believe the odds are high for it to be a preamp problem as there are 3 channels and for all to be bad would be not likely. if i had a huge volume gain thru the effects return i would say lets look at the preamp circuit ,but thats not the case.any ideas?...thanks...ed!!
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: DrGonz78 on July 30, 2013, 07:47:54 PM
Here is the power schematic for a mini-brute and I am pretty sure they are very close. Look on the board for where the transformer plugs into the power board. Should be easy to start checking for voltages around caps too. Look at the regulators to provide other various voltages to the preamp...

P.S. I could not find the thread where I got these pics... I searched but could not find it... Thanks to that poster for these pics and schematics.

Double P.S. The 378B looks more like it here it is...
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on July 30, 2013, 08:40:37 PM
i can check the parts on the board ,but i need to extend the wires that go to the connectors as they are only about 2-3 inches long.i can't turn the board upside down to get at the board with this situation to measure anything with the power on due to this situation..i measured all the capacitors. transistors were checked with a diode test on my fluke 87iii meter and a radio shack diode tester and they all tested good.all resistors and diodes were also good.solder joints looked good.both 50volt 8200uf capacitors were checked and measured good on my sencore ca55 capacitor checker which tests caps under a load.if i had 4 molex connectors of the right size and gender i could extend the wires and check everthing.i'm sure that is what they did at polytone when they were in business....ed!!
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: J M Fahey on July 31, 2013, 12:27:04 AM
That amplifier is crazy, it's a mess .

Quite probably it was kludged to use some surplus stock.

The channel PCBS are CRAZY: they look like "all inside one big PCB" jobs, with power amp and PSU together with the preamp ... and they filled only the preamp holes, leaving 80% of each board empty .... CRAZY.

That said, you were LUCKY because they used a "known" power amp, the exact same that DrGonz posted <3)

The only (unimportant) difference is tha the "official" one uses a dual transistor while the one to repair has 2 separate TO92 ones.

I suspect the Power amp works, that you have a connectors problem or something, but to check it, feed 1 or 2 V RMS 1KHz into what's labelled as "input" or "R1" into the official schematic.

Load the amp with 8 ohms (we don't want maximum power yet but to see how it behaves), scope it, and start raising input signal until output starts clipping, then back a little to *almost* clean.

I want to check whether we have a real sensitivity/power problem or not.

I guess not, but let's confirm.

And such problems are best solved in a *functional* way, checking how *systems* actually behave, compared to what's expected, not measuring part by part.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on August 07, 2013, 11:57:03 AM
sorry Juan!
  i worked on my car the other day and one of my knees has been hurting since.had to carry the amp down stairs to the basement where my funtion generator and scope are.that is why i am posting this so late,sorry!! i'm not sure what i have to do here. i have the signal generator on 1khz with a sine wave and i just switch between the voltage scale and the time scale on the scope and with the signal generator and scope clips attached to each other i get a sine wave on the scope.when i clip onto a 1/4" input jack with the signal generator and attach the ground lead of the scope to a speaker terminal and probe the other speaker terminal i don't get anything on the scope. it's probably me. i switch the scope thru different voltage scales and time periods with no result.....i really need help with the scope. i tried to calibrate it by touching the calibrate with the test probe and tried to make a connection with the ground connector on the scope and when i turn the calibration dial i see little difference.guess i need some tutoring with this .its a b&k scope....ed!!
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on August 08, 2013, 04:30:36 PM
thanks for the schematic dr gonz78.the schematic number pa378b is the right schematic.the output tansistors are listed that i have mj4502 and mj802.i will try to check things out for you again juan.i goofed up i carried the unit back upstairs to get the transistor numbers off the transistors and i noticed i forgot to hook up the rca cable to the output board, so i didn't have a preamp signal going to the output which = no scope pattern.i screwed up sorry. i will redo the check for you later tonight....thanks...ed!
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on August 08, 2013, 08:27:27 PM
i have a B&K 2120b scope (30mhz) and a Tenma 721005 work station.i set the scope @ 2v and the time @ .2 and when i touch the cables from the tenma with a sine wave and 1khz signal the scope give me a great looking pattern.i attached the clips from the signal generator to a 1/4 inch plug and plugged it into the input of the amp.i tried going across the speaker with the ground and probe.i get nothing.no difference with the volume and master volume controls.i unplugged the rca jack coming from the preamp i am guessing and get no change there either(just the straight line on the scope) going from ground (the outside of the plug and probing the tip ..going to try to get voltage readings with my fluke from the base and emitter of the mj4502 and the mj802 output transistors.By the way my friend that called polytone got a call from Diane today. he happened to be not home,so he is going to call them back tomorrow.if i get ahold of a print for this monster i'll try to pass it on to the rest of the ss guitar site if possible...ed!
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: Roly on August 09, 2013, 11:12:36 AM
Try working forward from the back of the input socket, reducing the sensitivity of the CRO as you go stage by stage.

But first...

Quote from: Roly
Can you find good main power rails, like +/-33 volts?

Can you find good preamp supply rails, like +/-15 volts?

Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on August 09, 2013, 04:49:33 PM
hey gang! i had a heck of a time getting the alligator clips on to the emitter of the transistors.i got +36vdc on the MJ4502 and -36vdc on the MJ802,so i have no power supply problem. i am guessing what i am getting from the amp is all shes got.i'm thinking that it is overated by polytone.unless there is say 10 volts on the 15volt supply for the preamp.i mentioned earlier that the trace was cut at the opto isolator which is right after the large probably 3amp diodes on the first preamp board.i don't know if it was cut at the factory or someone cut it by accident.don't know if i fix the trace will i get smoke. who knows without a print.my buddy called diane back today and got the answering machine.looks like Roly wins this round.no answer from Ploytone....not counting on getting a print for the preamp section..thanks for the power supply print. it was right.i'll try to get a voltage reading off one of the voltage regulators legs and see if i get 15vdc supply voltage......ed
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: Kaz Kylheku on August 10, 2013, 01:06:32 AM
sometimes i can hold a key down and the volume will jump up to full volume for a split second if i pick the right key to hold.

That sounds like it could be a problem with the keyboard (in addition to the amp problems). Do you have another amp with which the keyboard can be shown to behave itself?
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: Roly on August 10, 2013, 10:27:16 AM
Nope, nobody wins.

It's starting to look like the horror stories around the net are right, and one has to wonder about a company that is so careless of its good reputation.

JM remarked on the dubious internals, and it's in keeping with the saying that "you never find just one roach in a kitchen".

I am simply boggled by the claim that they refused to service a brand new amplifier that turned up faulty; but given that claim it should be said that it is possible that this particular amp has never worked correctly and has been doing the rounds.  Still, if you fix it it's a feather in your cap.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: J M Fahey on August 10, 2013, 11:18:15 AM
Polytone used to be a small but serious Company, but like many similar ones, based around *one* person, not a team.
If that person starts failing, for whatever reason, the Company may well go down the drain.
I long suspected Mrt Tony Gumina  (Mr Polytone) has passed away, and maybe a widow, or children who are not into Electronics ut something else, are trying to keep it running.
Just checked, Mr Gumina is still alive, but being 82 it's not that unlikely that he had some kind of health problem.
Hey!! Just being alive at 82 is already an accomplishment !!! :)
I imagine a small, Family type Company, being run and staffed by elderly, retirement age people.
Even their Web Site, up to a very short time ago, consisted of scanned (paper) Catalog pages !!!
And they had no EMail but you had to **Phone** them !!!

This particular amp, the "made for something else" PCBs, the weird "let's add something else to an already designed panel, wherever it may fit" stringly hints at "let's use some unused/unsold stuff lying around".
Pity, because the product used to be good, and the idea very innovative.
FWIW: http://www.polytoneamps.com/index.html

By the way, they *still* list phone and fax as only contact means  :o

Mr Tony Gumina himself in 1950 (do the Math):
(http://www.polytoneamps.com/widgets/gen_1116.1.gif)
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on August 10, 2013, 03:52:31 PM
got a call from Polytone and a e-mail that said they were sending me a schematic usps.will let you all know if i get it. diane seemed to be very nice on my answering machine. seemed like a nice lady judging by her voice.I tested one of the regulators on the 1st preamp board and i got -15vdc.I didn't find the +15vdc yet. i powered up the amp and ran a chord from the Polytone send to a traynor 20 watt amps return and the volume is low.must be a preamp problem.i need to verify the output section the same way as the volume is lower than what i had previously.if i get the schematic. i can use my signal tracer and check the ic's ect for signal starting at the inputs...
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: Roly on August 11, 2013, 01:43:43 AM
Quote from: JMF
the weird "let's add something else to an already designed panel, wherever it may fit"

I sat here for some time initially looking at the control panel layout, scratching my head trying to figure out the signal flow, and why it seems to depart so radically (and confusingly) from convention.

Meanwhile @Ed, track down those power supplies - no amp can be expected to boogie if it doesn't have the right supplies.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: phatt on August 11, 2013, 06:13:29 AM
Something to consider,, This is likely NOT a guitar amp, it's a line input mixer Amplifier package ..
So if you are plugging in an electric guitar then don't expect it to be as loud as the average Mega Gain guitar Amp. 8|

If all controls work then I'd hazza guess the amp is working fine you just need a dedicated Axe preamp in front and all will be fine.

I own and use a keyboard mixer amp so I'm familiar with the not so gainy inputs.
Just quietly,,, lower gain Amps like this are far more versatile. :-X
Phil.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: Kaz Kylheku on August 11, 2013, 10:37:58 AM
i powered up the amp and ran a chord from the Polytone send to a traynor 20 watt amps return and the volume is low.

I'm afraid that no hard conclusion can be drawn from this type of thing. We would need some assurance that the line levels in the effect loops of the two amps are nominally supposed to be the same.

Jumping volume levels can be caused by worn or dirty potentiometers, due to the wiper making an intermittent contact with the resistive element.

The first thing to do is give the unit a thorough cleaning: pots, jacks, and any switch contacts that carry audio that you're able to reach with spray or swab.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: g1 on August 11, 2013, 11:59:52 AM
i powered up the amp and ran a chord from the Polytone send to a traynor 20 watt amps return and the volume is low.must be a preamp problem.i need to verify the output section the same way as the volume is lower than what i had previously.
  Verify the output section by running the send from the Traynor into the return of the Polytone.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on August 14, 2013, 11:13:00 PM
i am supposed to get a schematic from polytone from Diane. it is supposed to be in the mail.i tried the effects loop with my traynor 20 watt tube amp and got very low volume using the traynor as a preamp and the polytone as a power amp and also got low volume with the polytone as a preamp and the traynor as a power amp.the only thing i question is that the polytone has what is called a main out.is it a preamp out,speaker out,power amp out.need a manual that identifies what it is.maybe thats why i didn't get volume using the polytone as a power amp.as i hooked the traynor send  into the effects return of the polytone.i don't have the volume i had previously.i am guessing i might of not hooked up a connector before putting the two back boards on the amp again. i thought i plugged everthing in ,but now i/m not sure.i've lost my patience with this thing and i am going to wait till i get the schematic to renew my interest in this thing...Ed!!
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on September 21, 2013, 02:11:18 PM
got the schematic from poly tone.i have to figure out how to downsize it.i found out that i have the - 15v supply ,but lost the +15v supply. if i touch the regulator it gets hot.something is loading it down.i have the +24volts at pin 1 of the pnp regulator.any suggestions on locating the short that is loading down the regulator.i only get .003volts going to the ic socket of the +15v.the -15v is present. i replaced the regulator and got the same results.now how to find the part that is shorted and loading down the circuit.Roly,enzo,and juan ,i am going to leave my e-mail adress.if you want a copy of the schematic i will send one to you (polytone taurus elite).i have the power supply and another print with everthing else.the only problem is the print and the circuit board numbers don't match as they use the same circuit board for all three channels,but it does allow you to go part by part thru the circuit.....edwardeffect1@yahoo.com....thanks...ed!!
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: DrGonz78 on September 21, 2013, 08:09:34 PM
Here are the schematics for the Taurus Elite amp... Ed sent them over to post up here for convenience. Thnx Ed!
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: Kaz Kylheku on September 21, 2013, 10:59:35 PM
Don't overlook the possibility that what is loading the regulator down could be ... the regulator itself, due to being toast, with an internal short.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: DrGonz78 on September 22, 2013, 02:26:56 AM
Yeah sure the regulator could be the problem but I think Ed said that he had replaced the 78M15 part. In this case I would be checking zener diodes or resistors for shorts. ZD3-6 and all zeners need to be tested. Also, voltage check of the 24volts rails needs to be established as well.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on September 22, 2013, 07:56:44 AM
thanks Dr Gonz for posting schematics.all diodes on the board with the 15v supply regulators test good with a diode test. both 24v supply rails are present.when i do the pinkie test on the regulators.the new regulator i installed is getting hot to the touch.something must be loading it down.getting .003v output from it.now how to find the shorted part that is doing this?i have tested all the capacitors with a capacitor meter and also checked across the leads of the caps on low ohms of my fluke for shorts and i haven't found anything.also tested a transitor on the board and it is good also.there is a trace cut near a opto- isolator.i believe it was done at the factory and it doesn't seem to be in the same part of the circuit as my problem.as the amp previously did work with this same condition.just didn't seem to have 130watts.previously i found 2 wires detached from the unit.a black wire on the regulator board and a purple wire in the reverb board. they have been repaired.that is all i have for now. open for any ideas for testing for the short.guess it could be on any of the board with the 15+v supply.thats alot of parts to check.might not be on the supply board ,but may be on another board in a later part of the circuit.tough to test do to layout of boards all sandwiched together vertically.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: DrGonz78 on September 22, 2013, 12:14:43 PM
Is there a way to detach the power board wires that carry 15v rails to the other boards? I mean at least then we could test the voltage at the source just to make sure it is good. That way we can then start looking at opamps etc etc... Well then again... So far it sounds like the +/-15v rails are being bogged down by something upstream. Are any opamps getting hot in conjunction with the regulator getting hot?
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: Roly on September 22, 2013, 01:16:54 PM
Quote from: DrGonz78
Are any opamps getting hot in conjunction with the regulator getting hot?

Yup, or, paradoxically, do any of the op-amps seem to be stone cold while the others are just warm?  Both hot and cold conditions are suspect.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on September 22, 2013, 02:20:31 PM
the -15v regulator is slightly warm and at proper voltage.the +15v reads .003vdc and gets hot to the touch.going to do a pinkie test on the op amps as dr gonz metioned and see what i get.i removed 2 op amps from the reverb board as there was a capacitor arcing due to a bad solder joint.thought that an op amp might of got fried ,so i removed them from circuit and it had no effect on the regulator voltage...off to the pinkie test. was outside fixing a broken brake line and bleeding brakes. back to the amp....ed
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: Roly on September 23, 2013, 11:01:01 PM
Quote from: EDWARDEFFECT1
the +15v reads .003vdc and gets hot

So it's a pretty fair bet that there is a short somewhere on the +15V rail.  The current path can sometimes be found by very careful low voltage measurements - a shorted chip will be the one with the least voltage across it (or its supply to its local ground).


I've been asked to explain why a defective IC or semiconductor might be cold.

Mostly when a semiconductor fails it still has some resistance, sometimes quite a bit of resistance, and as it draws current from whatever supply it dissipates power, P = I2R, and gets warm or hot, giving rise to the "burnt finger test".

It is also possible that it could fail open circuit, say due to excessive current burning out the fine interconnects between the external leads and the chip like tiny fuses.  No current, no heat.

The other failure mode can occur when the chip suffers a catastrophic failure and melts down into a conductive blob.  This can happen when mains voltage gets to low voltage circuits and IC's get a blast of current in reverse, where the bulk chip substrate gets forward biased, and the whole complex IC looks like a very simple forward biased diode, passes massive current, and simply melts.  In this case the result may be a chip that has only a few ohms of resistance, and we have the opposite case, current, but no resistance worth talking about to generate heat.

Power, thus heat, can only be dissipated in a resistance.  Both open circuits, and dead short circuits, have no resistance, thus generate no heat ('tho a short may well generate a lot of heat in the power supply).

As always you should suspect the odd one out, a chip that is hotter, or colder, than the others around it.

HTH
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: J M Fahey on September 24, 2013, 01:38:47 AM
Solving that kind of problem is pesky because "1 shorted part makes *all other* parts connected in parallel with it alsi look/measure shorted"
which in practice means that if you have, say, 15 IC's fed from same pair of rails, you'll have to pull them all, one by one, until the short disappears .... ugh !!!

*But* in this amp, thanks God you have 4 or 5 PCBs interconnected by physical wires, so follow the path from +/-15V source until the furthest IC and lift wire pairs in due sequence, until +/-15V reappears at the PSU, then you'll have to pull only a hadful of ICs.

And if removing the full Preamp still shows lack of +15V, then the short is in the cap immediately following it or in the connector, if any.
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: EDWARDEFFECT1 on September 25, 2013, 02:45:47 PM
i pulled all the ic's and still no +15v.all were in sockets thank god!i found a solder bridge between a black ground wire and the positve of the circuit. it has been corrected.the big short is gone,but apparently i still have one to find. i found 2 capacitors with bad solder joints and fixed them with buss wire as i think the trace was loose or missing(coudln't solder,so i followed the trace to the next component and buss wired the lead to the next component).all fixed now!i took the preamp board outside to get really good look in  natural light and looked it over with a fine tooth comb.i found a solder bridge on the one board and opened it up hoping that was my short to no avail.when i turn the unit on the +15v reads 11vdc then diminishes to 3vdc.still something drawing voltage from my supply.when turning the amp on there is a loud squeal.when we hooked a guitar to the input it had a loud guitar sound and squeal for about 4 seconds then nothing no squeal due to lowered voltage.....ed
Title: Re: Polytone Taurus Elite amp low volume no schematic!
Post by: J M Fahey on October 02, 2013, 09:37:53 PM
Sorry but now it's in your hands, only you can physically look at it under good light and a loupe.
Anyway, if pulling all IC didn't solve it, then start from the o0ther end: disconnect the +/_ 15V supply from *any* load and check whether you recover normal voltage.
If not,check the supply itself.
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