My AD120VTX has been in the hospital for over a month now...

[Telegib]

Thought I'd share this...maybe someone can shed some light on this problem...

Let me start by saying I'm sure glad I have a backup AD120VT.

I took my 120VTX into a authorized Vox Repair house on Oct 3. The amp was "crackling" and this terrible cracking noise coming through the speakers. Sometimes it would stop, sometimes it was keep doing it.

I spoke to the technician this morning and asked what he has found. He told me the issue is intermintent and it's been very difficult to identify exactly where it's at. He said he originally thought bad tubes, but after further checking he said my tubes were fine and that wasn't the problem. I asked him about the sockets and signal path.... He said it's not in your sockets either or signal path - he said it's happening after that.

He mentioned it might be a " leaky semi conductor", or "transistor" or "diode". He said there are hundreds of these in the amp so it's difficult to nail down which one. He did say this happens more often when the amp is cold and has not been on for a while. I am no electrician or musical equipment buff and very ignorant to the inside workings of an amp so I have no idea what all this means. Anyway, he said he will continue to monitor and check it on the bench, but right now, it still has this problem.

Any thoughts, suggestions, comments ?

Thanks.

Scott

[jacobri]

Is he really 'certified'? Does he have a real schematic at least? As a quality check of his expertise (if you are in doubt), ask him to re-trace what signal paths he has reviewed.I would expect buy now he knows if issue is common to all or he has narrrowed down to input stage, pre amp, power stage, speakers, etc...

Does it happen for all signal paths;
- Isolate stages
> Pre amp and/or power stage both making noise?
> Inject signal into power stage
> Eliminate speaker, use headphones
> Does it follow speaker if you swap leads, or follow leads?
- Isolate which side, or both
> put open ended jumper on effects loop for just one side and switch
> Is it common to both sides?

I had a low power, intermittent sound and took my guy a few weeks to figure out.

May want to see how much he will charge for his learning curve time?

Good luck amigo!

[Voxman]

Dry solders are one of the most common problems - get him to check & if needed, resolder all the main points (I think there's 7 or so)

[Telegib]

Update....It's been in the repair facility since Oct 3. I have called a couple of times to check in to see what they found.....always to be told, nothing yet, still have it on the bench testing it. Anyway, got a call last Friday....said you can come pick it up. They told me they don't know whats wrong with it but recommends I send it back to Vox ! Told me it would be better sitting in my house than their bench. WTF.

[Telegib]

now....they only charged my $17.50, which is fine. Unfortunately I have a non functional amp.

[jacobri]

If you want I can give you the contact info for the guy that fixed my ad120vt. He need to go through the schematics thoroughly so he kind of knows the amp. He's young and he its trying to get into three business. Nice R.I.T college kid. He Lives in Rochester.
Let me know...jake
Rich_jacobson@Yahoo.com

[Telegib]

Sure thing Jake. I'll take the info. Much appreciated.

The tech heard the problem but it so intermintent(sp?) it was hard to detect where it was coming from.....so he said the amps is working fine now, but he suspects the problem will arise again and to bring it back again "while it's doing it" and he'll discount his bench time cause I've already paid that today but again, he said he could not isolate the specific issue.

Thank you.

Scott

[Telegib]

Thanks Jake. Got the email and info. I emailed the shop and will see. I'm in Cleveland but my company has 2 branch locations in NY ( Syracuse and Binghamton) so I just may have to take a trip up to NY and drop it on Rochester on my way through...we'll see what he says. Thanks again. Much Appreciated.

S.

[Paragon]

Best thing to do is to either clean the jacks, or just replace them, and reflow the solder on the back of the main power board. I would think that should take care of the issue.

[jacobri]

DITTO!!