Rocktron Velocity Issues

[gtr-fxr]

Hi everybody,
I am having some issues with an older velocity 300 power-amp. i bought it used in non working order and had no idea it was gonna be this much of a pain to trouble shoot.
after i took out the tin-foil that was stuffed in the fuse holders , yep tin foil! i noticed a few problems -50vdc everywhere and several resistors started smoking R5,6,10,11,28,29 C46,,47 U9,10.... you get the idea.
so to make along story longer after some help from some members at FSB i built a current limiter replaced all known bad parts and began testing only to find more bad parts.. i believe Q13,17,35,31 are also bad "read 5 ohms in any direction" and i wont have replacements for a day or so, but i decided to try testing anyway. another bad idea I'm sure. but so far nothing is blowing up but i did notice Q22 is extremely hot . always was as far as i can remember,but cant figure out why. any help is greatly appreciated

[Chuck H]

"-50V everywhere" would be a good place to start. If a power supply that is supposed to be regulated to some lower voltage is failed that would certainly cause problems with any transistors which rely on it.

BTW, I can't say why, but your attachements don't open.

[gtr-fxr]

well i think i have the -50v situation somewhat under control. after replacing U9,10 but as of now when i go to put in fuse 2 "on ch1" my light bulb limiter gets really bright.i'll try uploading a new schem.

[teemuk]

i'll try uploading a new schem.

Don't bother. It's not the attachment being faulty, it's this forum software; just one of the several and several issues with it (e.g. my browser will fail as soon as I press the "submit reply" button. Anyway, the pictures are just fine when you save them to your computer. Trying to view within this forum platform just doesn't work.

[Chuck H]

All I can get is the thumbnails.

[Jazz P Bass]

I cannot even view them.
They do not download (ie: no activity on my router)
Here are two from a previous post.

[J M Fahey]

The drawings are HUGE.
My Firefox choked on them too.
I had to (right mouse button click) "save as" them and then open them with IrfanView.
The "power section" is 7686 x 2380 pixels; the "main schematic" is 8128 x 4608 px.
Sometimes too much of a good thing is not good any more.

[gtr-fxr]

see if this is any better

[gtr-fxr]

ok so i replaced Q22 .that ones fine now buttt Q10 is over heating now

[gtr-fxr]

and U10 keeps going out thats why i was seeing -50v everywhere, but i cant figure out why it keeps blowing

[Chuck H]

I'll guess that one of the power supply components is bad or there is a short in the wiring. There's a bunch of caps and resistors in the power supply. Have you checked them ALL for spec.? If U10 is failing repeatedly we should be able to rule out that U10 is the cause. So what's causing U10 to pass too much current and fail? Check all the -V power supply components and anything operating on -V.

[Jazz P Bass]

U10 is the -18Vdc rail.
If it is being killed (not dying) then something is pulling way too much current through it.
Look for an IC that gets hot (after you have installed a new U10)
Build a lamp limiter.
Again, if Q10 is getting hot, either it is bad or the circuit it feeds is pulling too much current.

[J M Fahey]

Agree and add: U10 is feeding 18V to different parts of the circuit, such as the output relay driver, the input preamps, and the over voltage relay and associated circuitry.
Follow the path from U10 to those different "clients" and cut proper tracks, one by one, until you find the damaged system; then pull ICs from that area, one by one, (one of them must be shorted) until you find the culprit.
Just one suggestion.
Be systematic, go step by step, donīt shotgun replacing everything "just in case".
Good luck.

[gtr-fxr]

OK im finally getting somewhere with this thing! found a bad transistor on the -18v side so now my voltages seem OK. so far so good with the current limiter plugged in i get a very dim light. good sign? i hope.

[gtr-fxr]

scratch that last part. something on channel 1 just went bad and blew c8