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Accutronics Reverb problems. Like Nothing (old Randall) SOLVED!!!

Started by ToadMeister, May 05, 2017, 10:12:46 PM

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ToadMeister

#15
Quote from: phatt on May 07, 2017, 07:34:38 AM
With transducer connected and you have continuity from hot to ground at the cable termination inside the amp then the circuit should work. If it does not work then pull the tank apart and check the springs are not broken.
The tank looks fine physically, inductors show continuity, nothing broken.
QuoteThe tiny wires that run through the magnet often break which is not normally fixable. :'( 
They are OK, and not fixable? Give me a guitar string and a soldering gun and we'll see. But never mind, everything is intact.
QuoteIf the drive end is broken but PU end is still intact then the pickup end will still make a clang if you shake the amp, giving the impression that it still works.
I've had a few Amps with that issue, especially if stored for long periods in humid/damp environments.
Phil.
It does that, but what about dampness? I live in a fog belt in Eastern Canada, what does the humidity do?
If things didn't break, we wouldn't learn how to fix them or know how they work, and things wouldn't get made for us to fix.
And there'd nothing to break.

ToadMeister

Quote from: Enzo on May 07, 2017, 02:30:07 AM
Nothing that complex.  Since the transistor sits at some voltage, if we just hook a cap to it, the far end of that cap will want to sit at that voltage.
OK got it, just standing by, not doing much but maybe holding a charge.
QuoteThe same voltage on both ends of the cap means it is not charged.   SO when we put some path to ground on the righthand end, that allows a charging path for the cap, now the left end charges to the voltage in the circuit, while the other end stays at no DC volts.
It could be a filter cap, or a charge dump cap in this configuration?

QuoteC43 is doing the exact same job as C42 one stage earlier, it is just a larger value so it can pass enough juice for the reverb transducer.  Single supply power amps use the same thing - a big cap - at the speaker output.
So if they weren't full up to their potential, they could be leaving the reverb thirsty, hence, not enough juice can be squeezed from these lemons.

QuoteYou can check it for ESR, but to stop working completely, that ESR would have to be sky high.
Is this mostly caused by electrolyte leaked out or evaporated, so that a charge can't get to the plates?
If things didn't break, we wouldn't learn how to fix them or know how they work, and things wouldn't get made for us to fix.
And there'd nothing to break.

phatt

Moisture and Steel = Rust, Even worse if you live near the seaside. :o
That is why second hand car dealers like to source there stock from inland where the climate tends to be dryer. Less rust. ;)

OK if the tank works then I'd be looking for cold solder joins in the drive circuit.
Often a gentle probe of the PCB with a wood skewer while running a signal will give you a clue if there are hairline cracks in the solder pads. It's often the larger components like Elcaps that are a problem as they are heavier, wiggle them.

BTW, just had another look at the schematic,, best I can make out is that only Ch 2 has reverb?
So if you are using Ch1 there will be no reverb. 8|
Phil.

ToadMeister

#18
Do you mean, all I have to do is put my jack into channel 2?
(I wish it was that simple)  :lmao:
In channel 2 I also have tremolo, which also does not work, I have sprayed out the pots with Lloyds brand 'Kleens-it' and worked the knobs.
I don't know if the tremolo and reverb share a bad solder joint or component, I get no response at all from the 'depth' and 'speed' tremolo knobs and reverb knob, but I am sure as I gather from your last post, SS components are themselves are not usually the problem, it's usually a physical problem.
I did go through the reverb with my probes looking for discontinuity, but I didn't work them with a skewer or the like, I cleaned out the plastic board to chassis wire connectors, and spread the male tangs with my jackknife to fit tighter in the females.
Could these two effects share a common fault? A bad solder joint would work sometimes usually wouldn't it? But muh oxidation might prevent continuity I suppose.

Now about the climate, it's damp, but I pulled a 1976 Sansui Stereo from the curbside and sounds awesome, the family stereo a 'realistic' is over 40 years old and still works great. (maybe caps don't dry out as badly here?)
The leads do have a slight patina, but then again the amp is ~40 years old too. And so is my guitar (I re-wired that thing with the Jimmy Page push-pull knob set-up and Darkstar pick-ups)
I ASSUME the tank is OK, it checks out OK.
When I check for volts at the drive output (reverb) I get volt readings with both the AC and DC setting, what is the output supposed to be, I have to hit the string hard for it to register 10v. If I only had a tank that I know works to tell for certain.

I guess I will do as you suggest and Shish-Kabob the component solder joints, I think the alligator clips will come in handy here. (wheres my other damn clips?)

PS, there was no voltage readings at the LDR (Light Detecting Resistor)
I think the reverb and tremolo share the foot switch jack?
If things didn't break, we wouldn't learn how to fix them or know how they work, and things wouldn't get made for us to fix.
And there'd nothing to break.

phatt

You can always do a little battery test to see/hear if the drive transducer is working.
With Amp on, remove the drive RCA lead from tank (Leave PU lead connected to amp) then plug in spare working RCA lead to the drive tank.
Then simply tap the open ends of the RCA lead with a 9Volt Battery a few times. That should give a decent boy-yoying to the PU side of the tank and confirm that the drive transducer does in fact work. if nothing happens then the drive transducer is the issue.

As for the drive circuit, check the voltages at the points shown on the schematic which says you should have about -14VDC at the collector of Q24. If that Voltage is way off then the drive circuit has a problem.
Phil.

ToadMeister

What a coincidence, I was just doing a search on touching a battery to the leads to the tank the other day and didn't find much at all, but I figured I already am throwing out enough questions to you guys, so I'll ask about it later.
(Does anyone get annoyed when you search for amp problems and all you find is FENDER info? Nothing against Fender, I have a 25w Bass amp that sounds real nice, 'Rumble 25' )

My reasoning was, that if it wants V, I'll give it V, but of course I forgot completely, it's just hard getting motivated after work, and when I do, I go to bed too late because I hate to put something down when I start and time flies.

So thanks for confirming that phatt, I'll try that tonight then.
If things didn't break, we wouldn't learn how to fix them or know how they work, and things wouldn't get made for us to fix.
And there'd nothing to break.

ToadMeister

Holy crap I ramble on, don't I?
It all started, way back in the day when I had difficulty reading and writing, then I discovered comic books an................

Just kidding, reverb tank, CONFIRMED OK!
Loud and clear out the speaker.
If things didn't break, we wouldn't learn how to fix them or know how they work, and things wouldn't get made for us to fix.
And there'd nothing to break.

ToadMeister

#22
Been tracing through for bad connections, so far everything is good.

But I am wondering about one peculiar capacitor, not that it's a bad one, but the wrong one?

C42  in the schematic calls for a 2.2 the one in my PCB is a 0.22 non-polar red chiclet.
wima mks 0.22 100-12
A bit underpowered? Makes me wonder if it's an original part?

Any opinions from ye masters?
If things didn't break, we wouldn't learn how to fix them or know how they work, and things wouldn't get made for us to fix.
And there'd nothing to break.

Enzo

SO tack a 2uf or 4.7uf cap in parallel with it and see if it helps.  A lot faster than us doing mental experiments.

ToadMeister

I have some 63v 1uf caps. (all caps are 100v at least anyway in the schem. But there is only 40 volts in that part anyway.)
Tired now and trying to figure parallel or series caps, i know the rules for batteries, series would add, parallel would average I suppose.
I have to go to bed.
Look into it tomorrow.
If things didn't break, we wouldn't learn how to fix them or know how they work, and things wouldn't get made for us to fix.
And there'd nothing to break.

Enzo

Parallel adds, so a 1uf parallel to a 0.22 becomes 1.22.  That will be enough to tell you if you needed more or not.  If that seems to be the answer, then go find a 2.2 or parallel a couple of 1s.

ToadMeister

Enzo, did as you suggested, still didn't work....BUT, on a whim bypassed C43 with my own 3.3uf cap and then Reverb-verb-erb!

I did solder on 2 x 1uf 63V caps, ain't hurtin nothin' probably an improvement, I don't really know.

I would like to thank you (Enzo) and phatt for all your pointers.

Now to figure out the no tremolo issue.
If things didn't break, we wouldn't learn how to fix them or know how they work, and things wouldn't get made for us to fix.
And there'd nothing to break.

phatt

Great to hear you fixed the reverb. :tu:

Re the trem,
Check the LDR, it's drawn as an incandescent lamp so it may have blown the element.
If it's still working I'd guess you should get a low resistance reading from R65 to ground.
Also check the trem circuit voltages.

Phil.

ToadMeister

As far as I know so far, (going to recheck it) I tested 0V going into the light side of the LDR, but, as you suggest I should check the LDR itself.
I'll apply the required voltage and see if the photo-cell responds.
I'll check voltages elsewhere too

Any updates and I will post it on my other thread on this topic.

Thanks
If things didn't break, we wouldn't learn how to fix them or know how they work, and things wouldn't get made for us to fix.
And there'd nothing to break.