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Author Topic: Crate vtx65  (Read 4952 times)

jbmdisco

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Crate vtx65
« on: June 19, 2014, 01:19:26 PM »
Hi, I have a crate vtx65 on the bench at present. First fault was relatively simple being a couple of pots with broken tracks which after a good deal of research manages to track down replacements. After doing the bench test with everything appearing to be functional - utilising the good old 100w lightbulb short circuit tester and a bench speaker, I re-assembled the unit to try it properly. Still plugged to the short circuit tester (thankfully) switched on to a loud hum and a bright bulb! Ok I had swapped out 3 op-amp chips to removed some distortion (I do this by de-soldering and fitting a socket to ease future changing). Replaced these chips again just in case. No difference.
I connected an external speaker through the socket on bottom of amp and bulb went dim and carried out a quick test with a mic. All working A1. Disconnected ext speaker, switched on again - Bright bulb, loud hum !!!. Disconnected internal speaker and switched on - no problem, reconnected int speaker - all works A1 so eliminate speaker fault.
Having powered up yet again with int speaker connected, again bright light and loud hum - however plugging a bare jack plug to ext speaker socket then removing it again allows the amp to work A1.
I am missing something really simple here.
Has anyone come across such a fault or hazard a bit of knowledge - I have attempted to Email Crate but their  website takes me to another which is closed.
I do not have a schematic for this amp either which would help.
Please can anyone help me out ???
Thanks
From Scotland UK

Roly

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Re: Crate vtx65
« Reply #1 on: June 20, 2014, 05:47:58 AM »
Hi jbmdisco, welcome.


Doesn't sound electronic, more like something really stupid like a loose contact on the speaker socket or plug, stray wire strand under the plug cover, shard of metal somewhere.  Very close inspection with a lens and bright light.


I had a car radio/tape player come in one time that was randomly blowing fuses (and looking at the fuse remains it was really blown to hell, hard short).  Top off, couldn't find a fault on the bench so a head clean and it went back.  A few days later it returned, same complaint, and again I couldn't fault it under test.

As it happened I dropped it on the floor as I was putting it on the "out" shelf, intending to look at the wiring in the car, and when I picked it up there was now something loose inside.  "Blast!" (or words to that general effect) so off came the covers including the base plate this time, and there inside was a two dollar coin and lots of marks showing where it had been sliding around on the base plate.  A bit of investigation showed that when it was tipped face down the coin would firmly jam under some wires, but when knocked free it was able to occasionally touch both the case and the 12V input.   :duh
If you say theory and practice don't agree you haven't applied enough theory.

phatt

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Re: Crate vtx65
« Reply #2 on: June 21, 2014, 05:03:05 AM »
Hi, I have a crate vtx65 on the bench at present. First fault was relatively simple being a couple of pots with broken tracks which after a good deal of research manages to track down replacements. After doing the bench test with everything appearing to be functional - utilising the good old 100w lightbulb short circuit tester and a bench speaker, I re-assembled the unit to try it properly. Still plugged to the short circuit tester (thankfully) switched on to a loud hum and a bright bulb! Ok I had swapped out 3 op-amp chips to removed some distortion (I do this by de-soldering and fitting a socket to ease future changing). Replaced these chips again just in case. No difference.
I connected an external speaker through the socket on bottom of amp and bulb went dim and carried out a quick test with a mic. All working A1. Disconnected ext speaker, switched on again - Bright bulb, loud hum !!!. Disconnected internal speaker and switched on - no problem, reconnected int speaker - all works A1 so eliminate speaker fault.
Having powered up yet again with int speaker connected, again bright light and loud hum - however plugging a bare jack plug to ext speaker socket then removing it again allows the amp to work A1.
I am missing something really simple here.
Has anyone come across such a fault or hazard a bit of knowledge - I have attempted to Email Crate but their  website takes me to another which is closed.
I do not have a schematic for this amp either which would help.
Please can anyone help me out ???
Thanks
From Scotland UK

No, not necessarily  ,, if that speaker has a failing coil or as Roly pointed too,, a intermittent short then the load at power up is extremely low and the circuit will latch up and not start. The bare jack test has no load and hence does nothing.

I've had a power stage lock up like that just by going from 8 Ohm speaker down to 4 Ohm.
It drove 4 Ohm load but you had to switch on Then connect speaker.

Others here will be better qualified to explain this quirk better that myself.
Phil


J M Fahey

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Re: Crate vtx65
« Reply #3 on: June 22, 2014, 01:02:16 AM »
IF amp powers up fine WITH light bulb limiter and WITHOUT speaker but not when powered WITH speaker that's :"normal" on many amps.
Turn it on with bulb limiter, without speaker, check that it does not have DC voltage on the speakers out terminals (say, < than 100mV DC) and then without turning it off add speaker.
Play some music.
If it works , it's fine and you can plug it straight into the wall outlet.

DrGonz78

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Re: Crate vtx65
« Reply #4 on: June 22, 2014, 01:31:04 AM »
Just to note that this posting was also on the MEF website and apparently the OP fixed the amp.

http://music-electronics-forum.com/t36849/
“A person who never made a mistake never tried anything new.” -Albert Einstein

Jack1962

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Re: Crate vtx65
« Reply #5 on: June 28, 2014, 04:33:51 PM »
have you tried a different speaker ?

Roly

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Re: Crate vtx65
« Reply #6 on: June 29, 2014, 03:21:46 PM »
Quote from: jbmdisco
I have been providing repairs to West Central Scotland UK for 11 Years, without any adverse publicity.
...
Crate products will now going to be refused due to lack of technical back-up

Just acupla thorts...

We all get "stinkers" from time to time, for one reason or another (and calling 4 times a day is "another"  >:( ).  I've been doing all this  :grr  for around 50 years and this week I made a false start on modifying an electronic drumkit.  I set off without a clear clear of where I was going, and I ploughed on manfully for a couple of days before I got the message (I'm no drummer, and this is a left-handed kit, so I was all at sea).

For me electronics is kinda like carefully calculated blundering about.


Ego gets in the way.  It's not about being right, it's about getting it right.

The fault is not in the equipment, that just is what it is, the fault is that you haven't looked at it in the right way yet for the fault to be "obvious".  Your problem in faultfinding is to build up a solid mental image of what the circuit is actually doing, and looking at it in the right way, shifting your perception until it clicks.

Follow the bit that doesn't fit.

Take copious notes (and job records, and these days a pix folder).

Consult.  It has been said that "you should never struggle with a problem for more then a couple of hours without calling someone".  This point is when you have run out of test ideas to try, or you can see you are running around in circles getting nowhere fast.  Many times simply explaining to someone what my problem is has exposed a logical flaw, something overlooked, a mess of data crystallises into a flash of genuine understanding.


"Why do you rob banks?"
"Because that's where the money is."

Set up to fix TV's - go broke.
Set up to fix cellphone - lotta people doing it, so survival is hard work.
Set up to fix guitar amps and stomps - it's a specialist area.

My specialty is the lost cause, the too hard, the impossible repair.  I spent many years in industrial and bio-med pulling rabbits out of hats, coming in on service jobs where up to four previous service organisations had thrown the towel in after well muddying the waters; no circuits, no supplier backup, no clues from the previous attemptees - an awful lot of applied basic physics got me there.

"So, what does it do?"
"How can you fix a machine if you don't know what it does?!?!"
"If it works on the known laws of physics and you didn't import it from some alien galaxy, I can fit it."
"Gee, that's a pretty bold statement!"
"Works for me."

A day or so later, a glue batching system which I never saw before or since, was working again.

So if Crates are unpopular orphans, and documentation is impossible to get, you specialise, you "rob banks", you trace the circuit and photograph every Crate that passes through your hands.  Find the substitutes and source of supply (and how to get the cases open  :lmao: )

Guy here got captured by Fender Frontmans ('orrible power amp), and my personal Raven sitting on my shoulder is the Farfisa Transicord, and related gizmos.  Many times in my life I've been forced to come to grips with equipment I really didn't like, and you just have to swallow it because only a small proportion of the gear you have to deal with is actually nice gear to work on/with.

"Where there's muck, there' brass"
(unpopular jobs are worth more)



ProTip: "Factory reset" is great when the owner is a techno-dweeb and has somehow, by random poking, managed to have remapped the default MIDI drumkit so the kick and floor tom were transposed, and the rest of the kit sounded like it was made out of cardboard.

Had it hooked up to the Twin-50 and the 15inch W bin with tweeters - Zounds! - it sounds like a workable facsimile.  Hell of a lot more portable for an old geezer.   ;)
If you say theory and practice don't agree you haven't applied enough theory.

J M Fahey

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Re: Crate vtx65
« Reply #7 on: June 30, 2014, 01:40:03 AM »
In fact there is a lot of Crate data out there, but they make ***many*** models so its statistically impossible to have data on all of them.
That said, for production and economy reasons most amps run in series, and any given year carry very similar circuits in apparently different amps, so often getting 1 circuit is useful for many.
They have used all kind of technologies but omce they were suspiciously close to peaveys, and later they used TIP142/147 based power amps by the truckload.
So post some power amp closeups showing also the power transistors, and maybe we can find a close enough one.
As an example, I don´t have the VTX65 but found the GX65 which may differ in the use of digital effects but might have basically the same power amp:

Jack1962

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Re: Crate vtx65
« Reply #8 on: June 30, 2014, 08:35:09 AM »
contact Loud Technologies , they will email you form to fill out a return , they will send you the schematic of any out of production amp they made .

Roly

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Re: Crate vtx65
« Reply #9 on: July 01, 2014, 12:11:48 PM »

Servicing electronics equipment.


{Circuit?  What circuit?  For years I helped keep the wheels of industry turning with nothing more than the seat of my pants and a DMM with a bent pointer.  Documentation, if at all, was an operation manual, and even when you got lucky with a service manual with circuits it was 5:1 it would be in a language you don't read.  ::)

You really wanna circuit?

Well you'll just have to trace it.}
If you say theory and practice don't agree you haven't applied enough theory.

Jack1962

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Re: Crate vtx65
« Reply #10 on: July 01, 2014, 01:50:55 PM »
lol I hear ya roly , that's all part of being a tech  :lmao:

 

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