help w/ peavey TNT 150

[pontiacpete]

This amp has a scratchy post pot. I replaced the pot and swapped out all the electrolytics in the area and the nearest ICs, checked resistors and changed the one .1uf cap closer to the input. At the moment I don't have a schematic, but I hope to have it by tomorrow morning. There is negative voltage on the pot as it is increased up to about -.9vdc. On a light limiter the light jumps up brighter as the pot is turned.

Does anyone have any advice?
Thanks in advance.
pete

[joecool85]

This amp has a scratchy post pot. I replaced the pot and swapped out all the electrolytics in the area and the nearest ICs, checked resistors and changed the one .1uf cap closer to the input. At the moment I don't have a schematic, but I hope to have it by tomorrow morning. There is negative voltage on the pot as it is increased up to about -.9vdc. On a light limiter the light jumps up brighter as the pot is turned.

Does anyone have any advice?
Thanks in advance.
pete

Which pot is it?

[pontiacpete]

the 'post' pot.  I'll will be putting up the schematic soon. 

I've tried everything here.  The only peculiar thing other than almost a -1v on the pot is the voltage on the IC directly above the pot.  It has -15 on pin 8 and 16v on pin 5.

[joecool85]

the 'post' pot.  I'll will be putting up the schematic soon. 

I've tried everything here.  The only peculiar thing other than almost a -1v on the pot is the voltage on the IC directly above the pot.  It has -15 on pin 8 and 16v on pin 5.

Without looking at a schematic I'm going to say that's where the -1 on the pot should be.  Normally an IC would have the same - and + voltage, just inverse.  IE - it should probably be +/- 16v.

[pontiacpete]

How can I post a schematic,  it's the 512kB?

[joecool85]

When you go to reply, below the text box you will see a plus sign and the words "additional options".  Click that then upload the pdf and hit post.

[pontiacpete]

It's not allowing me to post a 926KB schematic.  Is that all that's allowed or is there something I'm missing here?

[joecool85]

Try it again.  512kb is pretty small and was the old limit for file size.  I've upped it to 1mb (1024kb).  That should work for you.

[pontiacpete]

I think there are a couple of regulars of some sort that are not working properly,  there are vr1/2.
What do you think?  I changed cr21 cr25 also and I swapped in new c21 and c22

[pontiacpete]

here it is

[pontiacpete]

I changed the regulators vr1/2.  Now it is running -/+15v,  don't know why it isn't -/+16v. But it'ssStill scratchy.  I trace this neg voltage to the neg side of C26 and the voltage R49.  ON the other side of r49 there's -2.5v which is the same as that on U9B pin5 and 6.  PIn 7 of U10B has -10v.  Should there be -10v on pin7 of U10? Should there be negative voltage in pin 6 of U9?  I each of these IC, and the resistors seem to being what they're suppose to be doing, dropping voltage.  
Is it possible that it's ok to have negative voltage on a pot?  Are the new pots that I've put in possibly be bad?
I'm stumped.

[pontiacpete]

found an open trace where R65 , the crossover frequ.  pot was installed.  Thanks for the help.

[joecool85]

found an open trace where R65 , the crossover frequ.  pot was installed.  Thanks for the help.

Does it work properly now?  Are your voltages +/- 16v as I expected they would be?