Int. Vox

[drewl]

Got one of them newfangled Valvetronix AD50's, breaks up, crackes etc.
give it a whack and you can hear something loose.
Does it without the lone tube in it too!

Checking for loose/cracked solder joints etc.
is there a usual suspect or place to look?
Thanks.

[Mars Amp Repair]

Drewl,
I recall a post recently that referred to a cement block resistor that gets loose, but I'd guess that would be the kind of thing you've already checked. glen

[drewl]

Awesome, it seemed that poking around it yielded the noise the easiest, so I reflowed it and so far so good.
I'll have to whack it a bit more!

They may have known about this, because on this one instead of a cement block, it's a wirewound positioned away from the board.....it's a .47ohm so it prolly gets hot and we know that's
always trouble with pc boards.

[guitarwine_red]

re: Int. Vox

Hey Drewl,

I have copied the results of my investigation of a similar problem with my AD60VT - I might add that I used a magnifying glass to examine the likely week points, although what I discovered were fairly obvious.

I would not have found all of the problems had I not separated all of the PCBs from the chassis though.

"I pulled the amp apart last night - separated all of the PCBs and went over them with a fine tooth comb. One of the FX loop jacks was faulty and possibly causing a weak connection. I removed it from the board, disassembled it and got everything realligned and retensioned and fixed it back to the PCB. In addition I found that the external speaker out jack had two legs that were badly soldered and loose on the PCB - easy fix. I also found that the level control pot for the phone out and line out jacks had one cracked solder joint and one which appeared to have missed being soldered when the board was assembeled. Although the leg was in contact with the PCB it was an obvious weak contact - again an easy fix. The "large" resistor had one cracked solder joint. Tag2, Org2 on the main board also had a suspect connection. It was misalligned and had a very hit and miss solder joint.

I put the amp back together and gave it a real good workout and not a problem. I don't think that I have heard it sound so good. Even though I thought the amp was good from the start, it is even better now. The sounds on the clean amps are a lot cleaner and the higain amps are less muddy and noisy."

I hope this is helpful.

[drewl]

Thanks, that is helpful.
Luckily my real job entails surface mount work, so we have microscopes for inspecting plus $4k soldering stations that make it easy to work on 128 pin surface mount flat pack chips!

Another thing that seemed to help was resoldering the ribbon cables.

[Mars Amp Repair]

Drewl,
what kind of 'regular' job do you have with the flatpacks & all? g

[drewl]

RF amps transmitters and recievers, cell cite equipment, etc.
Also the power level pot on the back (dual 100k) was flaky FWI.

[Mars Amp Repair]

Nice,
I used to deal with the flatpacks all the time when camcorders & VCR;s were worth repairing. Funny how you can get really good at something like that & WHAM, they start selling for less that what's worth repairing.
It was a good run for some 25yrs. I learned a lot about uprocessors & discrete logic circuits, too. Comes in handy in Keyboards & pedal effects.

Also used all the fancy hot air & other desoldering devices..but for my money, ChipQuik is the only way to go.
Yeah, forgot about that switch on the back of those Vox's.

Happy soldering...glen