Quote from: joecool85 on February 18, 2011, 01:31:52 PM

Quote from: dan92y on February 18, 2011, 12:11:40 PM
OK, good advice.  If there is a broken wire or a strip that has lifted from the pcb, is there a way to fix that or not???  Thanks

You can repair them.  I've done it with a liquid in tube that I got from RadioShack a few years ago.  It has metal in it so once it sets up it works just like a regular trace.  I can't remember the name, but if you are interested I will check when I get home.

OK.  Found nothing as far as broken tracks or shorted solder joints that I can find.  Does someone know what I should look for (and where) to replace the pots that still may be the problem??  Thanks

Quote from: phatt on February 18, 2011, 07:06:59 AM
Hi Dan,
I'd be looking at R6 (50k Volume) and possibly R22 (50k Master)
If R6 wiper breaks from ground then the Amp would have very little gain but still pass a small signal. Which I believe is the symptom you described at the start.

Make damn sure you did not cold solder the new pots.
You need to inspect these things in very good light and even with a magnifiying glass.

Some of these modern Amps use very fine tracks and reinstalling commponents often lifts the track off the board.
A blob of solder may look perfect but cover a fine track that is broken.

I once built a circuit and inadvertantly bridged a very fine strand of wire as I soldered.
You can't see these things without magnification.

One tiny bit of hair wire caused me a week of frustration. :grr

As and old wise teck once said to me 90% of all electrical problems are in the connections,,,, I tend to agree

no matter,,, at least now you have learnt how to setup a DMM and use it.
Phil.

OK, good advice.  If there is a broken wire or a strip that has lifted from the pcb, is there a way to fix that or not???  Thanks

Quote from: dan92y on February 15, 2011, 03:27:11 PM

Quote from: J M Fahey on February 15, 2011, 03:05:42 PM
Well, it seems you *do* have +/-15V, great news.
Maybe we can get again on the right track.
Good luck.
PS: I had thought I was the only one who did not read instruction manuals. 

No, I try to shoot from the hip until I hit a wall.  I apologize for wasting the time before.  Also, I rechecked IC3 and have the following.
pin 1-0v, 2-0v, 3-0v, 4-14.1v, 8-15v.  Are those capacitors only to have voltage on one end?

I am starting to think that the pots may in fact be the culprit.  Any credence to this thought???

Quote from: CrazyEddie on February 15, 2011, 01:42:58 PM
Hello all!
I'm Ed, from the UK. I'm new here.

Now then. There's a dead Peavey Bandit on eBay, not far from me - the new style with the codpiece logo. The seller only says "The amp needs some repairs after a power surge at band practice."
What's the likely fault? Is it a major to fix? I'm pretty handy with a soldering iron.
Most of all, do you think it's worth the 45 quid starting price?
Cheers,
- Ed

Greetings.  I read your post and hope you don't mind input from a technological pygmie.  Get a working amp and save the hassle unless you are good at troubleshooting.  I have an amp that 'died' and am trying to fix.  The guys here have been AMAZING in helping me.  I Have NO CLUE how to troubleshoot these things and as much help as I have received on the forum, it has been frustrating as **$&&$!  Don't know your experience level, so I hope I don't insult.  Good luck and hope you get LOUD real soon.
Dan

Quote from: J M Fahey on February 15, 2011, 03:05:42 PM
Well, it seems you *do* have +/-15V, great news.
Maybe we can get again on the right track.
Good luck.
PS: I had thought I was the only one who did not read instruction manuals. 

No, I try to shoot from the hip until I hit a wall.  I apologize for wasting the time before.  Also, I rechecked IC3 and have the following.
pin 1-0v, 2-0v, 3-0v, 4-14.1v, 8-15v.  Are those capacitors only to have voltage on one end?

Quote from: J M Fahey on February 15, 2011, 09:18:26 AM
Or it might be set to Current.
Even worse, the Red probe could be plugged into the  2 or 10 Amp jack, which internally has a thick piece of copper wire (a shunt resistor) which shorts it internally to the black jack.
*That* will happily spark all day long.

BREAKTHROUGH- I plugged the meter lead into the CORRECT spot and got the following readings.
C38  25.1v - 0v
C39  25v - 0v
R74 - 25.2v - 15.1v
R75 - 25.1v - 14.2v
D19 - 0v - 15v
D21 - 0v - 14v
I apologize for the meter being plugged in wrong.  I am going back through the previous posts and re-measuring the ones you told me to do before as the meter has been this way the entire time. More to follow.

Quote from: J M Fahey on February 14, 2011, 06:42:19 PM

QuoteI assumed you meant check the ends of the 38 and 39 caps. to ground.  If that is NOT the case, that would explain the sparks.  Am I doing this correctly???

We are talking measuring voltage here, with a multimeter.
Sparks? ... what sparks? 

QuoteR-74 and 75 I would say are probably warmer than intended.  Not burning but pretty warm. NO voltage on either end but on one end they both sparked pretty well  D 19 and 21 are NOT HOT. NO voltage and on D 21 when I touched the probe on one end the speaker popped VERY LOUDLY.  Scared the ***** out of me.

Sparks? ... what sparks?  [2]

"No voltage" and "sparks" contradict each other.

OK I rechecked the readings.  D 19 and 20 ZERO volts DC and when I touch the probe to one end nothing.  The other end sparks when the probe touched it like a little static shock.  R-74 and 75  ZERO volts and sparked a little when the probe touched.  The caps same thing, but BIG sparks.  Maybe I should just send this to you...

Quote from: dan92y on February 14, 2011, 06:08:45 PM

Quote from: J M Fahey on February 13, 2011, 06:31:46 PM

QuoteI don't know if this matters or not, but...I ran a cable out from a good amp to the 'broken' one because I thought I could still use the speaker.  Out from the good on ext. speaker jack and into the crappy preamp one's input.  The dang thing came to life and nearly blew my ears out.  I had the controls set on the good amp for a descent level and when I played through the other amp it was incredibly loud.

Well, you shouldn't do that.
Speaker out signal is thousands of times stronger than a guitar signal and can (and will) fry your preamp input.
Maybe you got lucky and didn't but don't do again.
What you *can* feed there is the good amp's line out/loop send/pre out; 3 names for basically the same thing.
What happened somewhat confirms what I suspect, your preamp is dead or at least unpowered, and that strong signal just passed through it (unamplified) into your good power amp.

QuoteAnyway, like I said, Dont know if that makes a difference or not.  Also, is there a place where I can just get a new circuit board for this amp?  If I could swap out the whole board I would be in business, but I can find one online anywhere.

Commercial amplifier boards are never available on their own, except on the *very* unusual case of the factory closing and selling remaining inventory as-is, by the pound or, for example, Behringer sells new stuffed boards as plug-in replacement for their larger power amps, on the logic that they are used by Touring bands or in big house PA systems, where they just *can't* wait for repairs.
Anyway, not available for smaller amps, even more for an older one such as this.
That's why I'll soon offer in the USA some "universal" pre and power amp boards, to "save" amps like this which are basically 90% good.
Cabinet, chassis, transformer and speaker are , literally, "the bulk" of the amp, the most expensive part and the most difficult to solve for the home constructor.
Think a month or two ahead.

Back to your Harvard, let's check why you don't have those +/-15V.
At the Power Supply you should have +/- 25V on the ends of C38 and C39 respectively. (I think you do)
Then check on both ends of R74 and R75 ; you should have + or -25V on one end and + or - 15V on the other.
Are they hot? (use carefully your finger-o-meter).
Are D19 and D21 hot? (or warm).

OK I said before I am not an electrician/tech/etc.  I assumed you meant check the ends of the 38 and 39 caps. to ground.  If that is NOT the case, that would explain the sparks.  Am I doing this correctly???

I got more courage and tried some more.  R-74 and 75 I would say are probably warmer than intended.  Not burning but pretty warm. NO voltage on either end but on one end they both sparked pretty well.  D 19 and 21 are NOT HOT. NO voltage and on D 21 when I touched the probe on one end the speaker popped VERY LOUDLY.  Scared the ***** out of me.No blown speaker or fuses though.

Quote from: J M Fahey on February 13, 2011, 06:31:46 PM

QuoteI don't know if this matters or not, but...I ran a cable out from a good amp to the 'broken' one because I thought I could still use the speaker.  Out from the good on ext. speaker jack and into the crappy preamp one's input.  The dang thing came to life and nearly blew my ears out.  I had the controls set on the good amp for a descent level and when I played through the other amp it was incredibly loud.

Well, you shouldn't do that.
Speaker out signal is thousands of times stronger than a guitar signal and can (and will) fry your preamp input.
Maybe you got lucky and didn't but don't do again.
What you *can* feed there is the good amp's line out/loop send/pre out; 3 names for basically the same thing.
What happened somewhat confirms what I suspect, your preamp is dead or at least unpowered, and that strong signal just passed through it (unamplified) into your good power amp.

QuoteAnyway, like I said, Dont know if that makes a difference or not.  Also, is there a place where I can just get a new circuit board for this amp?  If I could swap out the whole board I would be in business, but I can find one online anywhere.

Commercial amplifier boards are never available on their own, except on the *very* unusual case of the factory closing and selling remaining inventory as-is, by the pound or, for example, Behringer sells new stuffed boards as plug-in replacement for their larger power amps, on the logic that they are used by Touring bands or in big house PA systems, where they just *can't* wait for repairs.
Anyway, not available for smaller amps, even more for an older one such as this.
That's why I'll soon offer in the USA some "universal" pre and power amp boards, to "save" amps like this which are basically 90% good.
Cabinet, chassis, transformer and speaker are , literally, "the bulk" of the amp, the most expensive part and the most difficult to solve for the home constructor.
Think a month or two ahead.

Back to your Harvard, let's check why you don't have those +/-15V.
At the Power Supply you should have +/- 25V on the ends of C38 and C39 respectively. (I think you do)
Then check on both ends of R74 and R75 ; you should have + or -25V on one end and + or - 15V on the other.
Are they hot? (use carefully your finger-o-meter).
Are D19 and D21 hot? (or warm).

OK I said before I am not an electrician/tech/etc.  I assumed you meant check the ends of the 38 and 39 caps. to ground.  If that is NOT the case, that would explain the sparks.  Am I doing this correctly???

Quote from: dan92y on February 07, 2011, 10:04:57 PM

Quote from: J M Fahey on February 07, 2011, 08:40:14 PM
Well, if you have no +/-15v rails your preamp is OFF , just like that.
Don't know if the preamp supply is dead or something (maybe a blob of solder) is shorting the rails.
I understand it's very frustrating and share your feeling.
Because of what's happening to you and many others, I'm considering offering an alternate solution, bypassing the problem completely.
It will consist on a couple "universal" preamps, easy to mount on a half-dead amp as yours, and happily driving the still alive power amp.
For all practical means, your amp will be alive and kicking and useful again onstage.
I see there are a few power amp kit offers, which solve half the problem, but none (that I know of) to cure the preamp by transplant.
Stay tuned.

Its still sort of fun messing around with all this stuff.  I have a grasp of what I am doing.  Just don't know WHY.  Thanks for all the help.  I dont know what you mean by RAILS. The transformer comes in and connects to the board and a small ground bus. Again, Thanks.

I don't know if this matters or not, but...I ran a cable out from a good amp to the 'broken' one because I thought I could still use the speaker.  Out from the good on ext. speaker jack and into the crappy preamp one's input.  The dang thing came to life and nearly blew my ears out.  I had the controls set on the good amp for a descent level and when I played through the other amp it was incredibly loud. Anyway, like I said, Dont know if that makes a difference or not.  Also, is there a place where I can just get a new circuit board for this amp?  If I could swap out the whole board I would be in business, but I can find one online anywhere.  Thanks again.

Quote from: J M Fahey on February 07, 2011, 08:40:14 PM
Well, if you have no +/-15v rails your preamp is OFF , just like that.
Don't know if the preamp supply is dead or something (maybe a blob of solder) is shorting the rails.
I understand it's very frustrating and share your feeling.
Because of what's happening to you and many others, I'm considering offering an alternate solution, bypassing the problem completely.
It will consist on a couple "universal" preamps, easy to mount on a half-dead amp as yours, and happily driving the still alive power amp.
For all practical means, your amp will be alive and kicking and useful again onstage.
I see there are a few power amp kit offers, which solve half the problem, but none (that I know of) to cure the preamp by transplant.
Stay tuned.

Its still sort of fun messing around with all this stuff.  I have a grasp of what I am doing.  Just don't know WHY.  Thanks for all the help.  I dont know what you mean by RAILS. The transformer comes in and connects to the board and a small ground bus. Again, Thanks.

Quote from: J M Fahey on January 23, 2011, 11:46:32 PM
Did you check voltages as in 5) ?
Did you put the s piece of wire I suggested after that?
As of IC3 it's easy, you can replace it by a very common TL072 or an RC4558, which is closer to the original.
Pay special attention to the small notch or dot which marks one end, the replacement should point the same way, but before changing it please answer *all* 5 questions.
Those are things you are checking for me because your amp is not on my bench, please do.
Thanks.

OK.  All the voltages were zero.  Replaced IC3.  Just had a trial run and NO CHANGE.  Officially I am about ready to give up.

Quote from: J M Fahey on January 23, 2011, 11:46:32 PM
Did you check voltages as in 5) ?
Did you put the s piece of wire I suggested after that?
As of IC3 it's easy, you can replace it by a very common TL072 or an RC4558, which is closer to the original.
Pay special attention to the small notch or dot which marks one end, the replacement should point the same way, but before changing it please answer *all* 5 questions.
Those are things you are checking for me because your amp is not on my bench, please do.
Thanks.

OK ALL voltages in step 5 are 0.00  I slipped and shorted pin 1 and 2 and the speaker popped very loudly (dont know if that matters) 
The wire between IC3 pin 1 and the node = no change when pin 2 touched there was a loud hum.

Quote from: J M Fahey on January 22, 2011, 07:11:00 PM
Good, so please confirm:
1) guitar or MP3 player into Harvard power amp sounds good, although not too loud, and without hum?
2) Harvard preamp to *another* power amp hums?
3) Harvard preamp to *its own* power amp hums?
4) If (3), please touch lightly with the end of a small screwdriver, pin 2 of IC3; does it hum loud?
5) If no change please measure (relative to ground) voltages on pins 1 , 2 , 3 , 4 , 8 in IC3.
They should be close to 0 , 0 , 0 , -15 , +15 VDC.
If still no change join with a short piece of wire pin1_IC3 to node (union) R52_C29 , then touch again Pin2_IC3.
Loud hum?

#3 HRVD preamp to own power amp = Yes quiet hum
#4 Crackles and louder hum when pin 2 of IC3 is touched
End of testing for this time.  Im guessing that chip is bad and needs replaced.  If so, where do I get the exact replacement?  I had a hard enough time choosing pots and I bet that there are even more types of IC's that will fit in the space.
Thank you very much for the tech support.

Quote from: joecool85 on January 21, 2011, 03:28:19 PM

Quote from: dan92y on January 21, 2011, 02:59:25 PM
Right.  Broken/pre-amp out to good amp input, good cord.  Good amp hums and no more. 

Ok, well then we know 100% for sure that it is a preamp issue.

OK. Now I am out of my 'lane'.  I feel comfortable replacing parts, but I don't know what to look for that is bad.  I can't tell from the print what is pre-amp, power amp etc.  Any thoughts??