Cloud VTX repair and restoration

I noticed a few corroded tracks, particularly at the front and rear of the bottom amplifier board.

no filters in any of the VTX750 or VTX1000 I had

kipman725 wrote: no filters in any of the VTX750 or VTX1000 I had

I think i have about every type of Cloud amp ever made. I had a question but i can't remember what it is now. Oh yea. Does anyone know what RV1 is for? RV2 is bias.
  What is the bias setting on the VTX is it correct that of the transistors are the Hitachi pair i set it to 100mA? So sometimes the main transistors are International Rectifier? I have the Hitachi in a CV1000 and Hitachi in VTX1200.
  Oh, i see VR1 is for offset it's marked on a CV1000. How do i set offset? is this for the speaker protection circuit to be balanced?
  In one of these amps someone has soldered fixed value resistors to the underside of VR1 so i wonder why they needed to do that.
  Fixed quite a few of these recently, one thing to note is never to touch both heatsinks at the same time as they are live, i got a shock and blew something on the amp.
 


Edited by izzzzzz6 - 16 March 2023 at 1:58pm

Hi Kevin. Thanks for the details.
  It almost seems they don't want anyone biasing these amps. I blew 2 fuses in my multimeter just slipping off of the small resistor and into the heatsink that also comes off of the same leg because it's not easy to get to the underside of the main balance resistors perhaps i should try to clip directly to the transistors leg.
  The VTX 1200 I have been working on has Hitachi fets.
One thing i found is that 2sJ119 and 2sk414 are quite expensive and a cheaper pair is available, the 2sJ118 and 2sk413 seem to be same spec except a lower voltage rating. Wondering if they are still within spec.
 Next time i will try to measure across each resistor at a time rather than going across both of them from fet to fet. One thing i noticed was that bias ran slightly lower at one end of the amp and slightly higher at the other end. I wondered if this could be tweaked by changing resistances but it seemed fairly insignificant.
  Yes, i had to glue a few of those relay magnets back on and the "rustling" sound was in one of the cv 1000's might even be one of the ones i'm fixing.
  Makes sense to have (backup resistors) on the offset, annoying when those pots go bad.
  I have so many amps to fix right now. Some of them are:
2x Cloud
2x Lab 6400
2x large QSC amps around 4k and 5k size
2x peavey 2600
2x harrisons (can't remember the model but fairy chunky ones for their age)

Recently sold a crest something 900, built like a bomb, had those cool bar led's.

Got another rare touring crest can't find any data on it but it's very powerful.

Lots of issues with DSP's have a broken 2x4 sabine which sends random tones out to random channels.

Still wondering why the BSS fds355 shuts down when brightness is adjusted and why all of the screens across my 3x units all have different tints / colours but at least they work if you leave them alone.

so many repairs lurking around here and also piled up at my dads in the UK. Hopefully will make some progress this year on some of those amps. Also lots of digital amps from powered speakers. Getting there slowly.

James

PS. 
    I currently have a good price on used Toshiba 2SA1302 ans 2SC3281.
Bigger transistors but same leg spacing, mounting holes are higher up, but other than tapping a new mounting hole on the heatsink I'm wondering if they could run in the cloud amps given a different gate / base resistor setup.
 

 


Edited by izzzzzz6 - 21 March 2023 at 1:42pm

I have 3 different types of clip on connectors but the ones that work the best i only have some hooked up to a component tester right now. Need to make some more leads up i have a bag of them somewhere.
  Those other fets share the same data sheet, how high could voltages get? Or am I missing something else. Rails are at +-~72V i believe.