Peavey Mace VT Problems

[g1]

You said the voltages checked out, does that include the + and - 15V at the IC's, and +15 at IR18 in the power amp?

[ric44]

You said the voltages checked out, does that include the + and - 15V at the IC's, and +15 at IR18 in the power amp?

No I havent checked any IC voltages at all. Only the tube sockets. How do I go about checking IC's ? I know the IC's are the little 8 legged black rectangles that plug into a socket. Just not sure how to check ? Sorry for my ignorance but can learn .

[g1]

Well, good to hear you haven't checked those yet, as the +15 is common to preamp and power amp and could explain why you seem to have problems with both.
Look for an IC labelled TL072, like U2 or U4. Check DC volts at pin4 and at pin8 (black probe grounded). See attached pic for pin numbering.
In the power amp section, look for a resistor called IR18. One side of it should measure +15V.

[ric44]

Well, good to hear you haven't checked those yet, as the +15 is common to preamp and power amp and could explain why you seem to have problems with both.
Look for an IC labelled TL072, like U2 or U4. Check DC volts at pin4 and at pin8 (black probe grounded). See attached pic for pin numbering.
In the power amp section, look for a resistor called IR18. One side of it should measure +15V.
[ATTACH=CONFIG]30899[/ATTACH]

Checked all the IC's that were numbered TL072 (there were 3 ) and on my meter I got 16+ volts DC on pins 4 and 8 . Also checked IR18 and got 16+ volts DC but on both sides of the resistor.

[Jazz P Bass]

You may want to recheck the IC power pins.
Looking at the IC pinout diagram, it is clearly stated that pin 8 is +(plus)VCC & pin 4 in -(minus) VCC.
So, unless there was a reading error on pin 4, you do not have the -VCC supply working.

[ric44]

You may want to recheck the IC power pins.
Looking at the IC pinout diagram, it is clearly stated that pin 8 is +(plus)VCC & pin 4 in -(minus) VCC.
So, unless there was a reading error on pin 4, you do not have the -VCC supply working.

Yes I rechecked and you are correct. Pin 4 is showing -16vdc on all IC's.

[Jazz P Bass]

Well that's good to know.

I forgot what we are trying to fix though.

[ric44]

Well that's good to know.

I forgot what we are trying to fix though.

Very low output, Normal channel input works, both effects inputs work, automix input does not work but does light both channel leds, have to really crank the buttons up to around 6 or 8 get decent sound . Sound output somewhat distorted ( scratchy ) . Reverb works, so does phase . At this point I have to ask what would the symptoms be of having some bad tubes ?

[g1]

One other fault you didn't mention, when you plug your guitar straight into Power amp In jack, you don't hear any audible sound.
Maybe double check this, hit the guitar hard and see if you can make out a slight sound from speaker.

[Justin Thomas]

^^^^^^^^^^^^^^^^ what g-one said! MUST fix power amp first - no point in checking anything else until you know signal will reach speakers!

Is it entirely possible there's more than one problem? I have a Deuce VT here, working fine... let me know if I can verify anything for you. Not identical, but pretty damn close...

Justin

[ric44]

Just double checked.....no sound at all coming from speakers with guitar plugged in to power amp in jack. Just to be sure here and make for certain someone hasnt juggled the plugs ? The power amp jack has a bakelite covering on back and has a thin black , a thin light green, and a bare (ground I guess ) wire connected to it .

[Justin Thomas]

On mine, looking down into the chassis at the in/out jacks:
Top lug (closest to me): bare wire connected to both other jacks' top lugs.
Right lug: green wire
Bottom lug: black wire
Left lug: no connection.
Looks fine to me...
I tried my guitar into Power Amp In - quiet, but definitely there and clean.
Justin

[Jazz P Bass]

Just double checked.....no sound at all coming from speakers with guitar plugged in to power amp in jack. Just to be sure here and make for certain someone hasnt juggled the plugs ? The power amp jack has a bakelite covering on back and has a thin black , a thin light green, and a bare (ground I guess ) wire connected to it .

My only guess (seeing that a preamp signal does pass through the jack) is that you have a missing connection to ground.

[ric44]

My only guess (seeing that a preamp signal does pass through the jack) is that you have a missing connection to ground.

Interesting that it could be something as simple as a ground problem. Ok so where would I need to look to make sure I'm grounded in the right places ?

[Jazz P Bass]

I knew I should have been more concise.

If the jack is not working as a power amp in, my guess is that the jack itself is most probably missing a ground connection.