Ad Widget

**Jazz P Bass** · 07-15-2013, 09:04 PM

First off, disconnect the speakers!
Break out your meter & see if you can measure any dc voltage on the speaker jack.
If so, the amplifier needs work.
I always test the power supply.
Both + & - rails should be the same.
You can access them right on the case of the power transistors.
Look for Vac ripple on the power rails & the opamp supplies.
The power rails can have a small amount of ripple.
The opamp supplies should see none. (pin 4 & pin 8)

**Enzo** · 07-15-2013, 09:53 PM

I agree^^^

Sounds like you have DC on the amp output.

I suggested someone steal a TL074 from the front end of a XR600C? The XR600B has a bunch in the front, but not the C. They are different amps. Suggestions like that are always in some context. Unless I was high, I would never suggest a bad TL074 for your symptom until I had already suggested isolating the problem to preamp or power amp, verifying all power supply rails, taking voltage readings and explored the likelihood of bad transistors and open resistors in the power amp.

**Jazz P Bass** · 07-16-2013, 12:24 AM

How to troubleshoot the repair of an amp.
"isolate the problem to preamp or power amp, verify all power supply rails, take voltage readings and explore the likelihood of bad transistors and open resistors in the power amp."

**Enzo** · 07-16-2013, 12:30 AM

(one two one two... I seem to be getting a little echo on my voice...testing testing...)

**Jazz P Bass** · 07-16-2013, 01:04 AM

That's going in the Enzo book.

**PepsiMoon** · 07-16-2013, 04:55 AM

I'm sorry Enzo ..I didn't mean to offend you.. Well I hooked up the driver board/power amp and checked for DC on the speaker jack, there was none. I checked the DC on the TO-3 output trannys. On the Left hand 4 outputs the voltage was 52.6 VDC on each. On the Right hand 4 outputs the DC voltage was 0. Thinking maybe the ground from my meter had come loose, I switched my meter over to diode/ continuity test and checked. I had a good ground connection. I was called away for just a few minutes by my dear wife. When I came back, I forgot to put the meter back on DC and touched my hot lead to one of the right hand output trannys. Immediately the main 8 amp fuse opened up. Yes, of course I'm very embarrassed.. But what's done is done. I pulled all power from the chassis, and discharged the filter caps with my trusty 100 watt light bulb. All 4 right hand outputs checked shorted, as well as the large diode just above them. I pulled out the plug with the red, white and blue wires going to the right side, and the outputs checked good, as well as the large diode. I traced back to the 2 identical small blue transistors mounted on small heatsinks directly to the preamp board. One checked good , the other checked shorted. I desoldered the shorted transistor and removed it from the circuit and tested it again. It was shorted. I plugged in the red white and blue wire harness, and the 4 outputs on the right side checked good as well as the large diode.Now not only do I have to figure out why the right hand 4 output trannys checked 0 volts, I have to try to replace the small transistor I accidently shorted. As I said before this is the 400BH Power Amp Chassis. The transisor is blue with a 'M' 5322.. 'M' being Motorola I would venture to guess.Thanks for the help so far.. An Embarrassed....................PepsiMoon BTW how do I post pics here?

**Enzo** · 07-16-2013, 05:39 AM

You didn't offend me, I was poking fun at Jazz for repeating something I wrote.

Look at the schematic. This power amp is quasi-complementary. The collectors on the positive side transistors are at V+. But the negative side output transistors have the output bus on the collectors. The V- appears on their EMITTERs. It is thus normal for zero volts on the collectors of those transistors.

You can get the exact 5322 and 5321 transistors from parts dept at PV. Get the schematics for the amp from customer service there.

**Jazz P Bass** · 07-16-2013, 01:24 PM

Schematic can be found here.
http://music-electronics-forum.com/a...7-pv-400bh.pdf

**Enzo** · 07-16-2013, 02:35 PM

AH, and points out the typo. Those transistors are 5331 and 5332.

**PepsiMoon** · 07-17-2013, 07:42 PM

Thanks Jazz P Bass for the link to the schematic..

Thanks Enzo for correcting my typo.. I just talked to Sherri at PV and I ordered two of each of the 5331 and 5332 and 2- 8 amp fuses. They're shipping out today..

I'm glad I have a new can of Deoxit 5, there are a lot of pots to clean while I wait. I'm in Oregon, so it'll be a few days till I get my parts. I wanted to add that I did some research on Bing, and found a free schematic for the XR-600C..

It's for the front end mixer section, and master board. Thanks for your help guys........... PepsiMoon

**Enzo** · 07-18-2013, 12:39 AM

Peavey will send any schematics you request.

**PepsiMoon** · 07-23-2013, 04:29 AM

Hello again!! I received the 5331's and 5332's and 2-8 amp fuses Saturday. I replaced both transistors and fuse and fired up the main amplifier section. I'm measuring +52VDC on the left hand transistors, and -52 on the emitters of the right hand transistors. 0 VDC on the output jacks. I switched off the unit and plugged in the Master Board from the front of the unit, switched on the Peavey and the noise has returned. Doesn't matter if the master volume is up or down , the noise stays the same regardless. I've checked various voltages using the schematic and all seems good. I found the main audio input wire and corresponding ground(after disconnecting the Master Board) and hooked up one side of my stereo pre-amp output to that, the hum, hiss, noise (whatever you wanna call it) gets louder, although I am getting good loud signal output. As I said before it sounds like there is a loose ground connection in the audio signal path somewhere. Anyway any help would be greatly appreciated....Thanks In Advance...PepsiMoon

**Enzo** · 07-23-2013, 05:26 AM

OK< so now the amp basically works, you can amplify music and it sounds OK. It just adds some noise, yes? No? And if you disconnect the cable to the preamp from the powr amp board, the noise goes away?

SO you have some hummy noise, and turning the master to zero has no effect? OK, you have a graphic EQ on there, do those sliders affect the noise tonally?

Plug a cord into the power amp in jack. On its free end, measuer tip to sleeve for DC, is there 15v there? If so, we have a shorted diode.

PLug a guitar or other signal into the power amp in jack. Is the hum present now? And does it amplify OK to the speaker?

Now plug the guitar/whatever into the graphic in jack. OK or not?

I don't recall, have we checked that ther is CLEAN +15 and -15 at the chips on the mixer panel?

**PepsiMoon** · 07-23-2013, 06:22 AM

Originally posted by Enzo View Post

OK< so now the amp basically works, you can amplify music and it sounds OK. It just adds some noise, yes? No? *YES* And if you disconnect the cable to the preamp from the powr amp board, the noise goes away? *Yes*

SO you have some hummy noise, and turning the master to zero has no effect?*Right* OK, you have a graphic EQ on there, do those sliders affect the noise tonally? *Yes They do*

Plug a cord into the power amp in jack. On its free end, measuer tip to sleeve for DC, is there 15v there? * No, 0 Volts Tip to Sleeve* If so, we have a shorted diode.

PLug a guitar or other signal into the power amp in jack. Is the hum present now? *No* And does it amplify OK to the speaker? *Yes*

Now plug the guitar/whatever into the graphic in jack. OK or not? *Yes ok, no hum, clean guitar sound*

I don't recall, have we checked that ther is CLEAN +15 and -15 at the chips on the mixer panel?

* No, we haven't*

Thanks so far ..

Pepsi Moon

Ad Widget

Announcement

Peavey XR-600C Mixer Head Noise

Peavey XR-600C Mixer Head Noise

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment