Peavey XR-600 400B/G

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Chaffeekid
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Peavey XR-600 400B/G

Post by Chaffeekid » Thu Jul 01, 2021 2:18 pm

Hi All. Been a while. Working on the Subject Amp. Initially 8amp fuse blown, 15+ supply 1 amp fuse on board also blown. 1 power transistor shorted, has been repaired before. Filter caps changed, now 4700uf at 71volts?

Checked all the cement resistors, all good on the power transistor board and on the main board. The Ugly Coil also firmly attached and the 22 Ohm resistor reads a dead short, so it is good per Enzo, in other posts :) I suspect the 5331 and 32 transistors, drivers may be bad.

I am going to replace all the power transistors with MJ15003g's as they are a mixed matched bunch now with 70484140 mixed in with the original sj16357's. Also going to replace the big Rectifier Diodes as one of them is also suspect.

The thing I can't find is a substitute for U2 listed as S7478 the little 8pin IC does anyone know what that could be, Thanks in advance.

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Enzo
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Re: Peavey XR-600 400B/G

Post by Enzo » Thu Jul 01, 2021 4:53 pm

Do yo have a reason to replace it? It is the compressor chip for the clip limiter. You can remove it from the socket and the amp will work - if all other things are right.

I recommend just replacing everything in the amp.

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Re: Peavey XR-600 400B/G

Post by Chaffeekid » Thu Jul 01, 2021 7:04 pm

Hi Enzo, well not everything, the chip has a crack in it from number 5 pin part way across the top. Apparently there is no replacement for it. I understand the Amp will work without the DDT chip. Thanks

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Re: Peavey XR-600 400B/G

Post by Enzo » Thu Jul 01, 2021 9:29 pm

I have them, but they are tucked away in storage.

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Re: Peavey XR-600 400B/G

Post by Chaffeekid » Mon Jul 05, 2021 9:56 am

I am working on the subject amp for the Church.

Replaced four of the power transistors, one was bad with MJ21194's substituted by the supplier for MJ15003's

Replaced all P600D diodes on the main board and two on the power transistor board, the 47 ohm resistors are good.

replaced both voltage regulators 7915 and 7815's from my junk box both are new.

Replaced the 5331 and both 5332's on the main board

Checked all cement resistors on the main board and the power transistor board, all checked good none open.

The unit blows the main fuse, but never the 1amp power supply fuses

I have only my Ohm Meter and a cap checker and limited electronic experience, have repaired a couple of amps before, this one has got me stymied.

77 year old Marine, still looking to learn something
Thanks for any help, Jim N0LZS

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Enzo
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Re: Peavey XR-600 400B/G

Post by Enzo » Mon Jul 05, 2021 10:45 am

Well, DO NOT connect a speaker or load until the amp is sorted. Also, look up "light bulb limiter" and make one and use it. A very simple tool that will prevent the amp from damaging itself further while testing.

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Re: Peavey XR-600 400B/G

Post by Chaffeekid » Mon Jul 05, 2021 7:51 pm

In the process of making one now Enzo any other suggestions I’m all ears.

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Re: Peavey XR-600 400B/G

Post by Enzo » Mon Jul 05, 2021 10:40 pm

It blows fuses now. We COULD disconnect the load and see if it blows fuses, but with a bulb limiter, all that happens is the bulb lights bright instead of fuses blowing. So that is the first thing we need to know - dos the load make a difference. If an amp makes DC on the output, it is the load that makes it draw excess current. SO if we find DC on the unloaded output, we then have to go through the circuit to find out why.

There are some voltages on the schematic, a good place to start.

Be aware that the bulb is for troubleshooting a fuse blower. The amp might function on the bulb, but not normally, so trying to measure circuit voltages while on the bulb will result in skewed numbers. We need to solve the gross problem first, then we can lose the bulb and chase down any nuance.

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Re: Peavey XR-600 400B/G

Post by Chaffeekid » Tue Jul 06, 2021 7:06 am

Thank you Sir.

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Re: Peavey XR-600 400B/G

Post by Chaffeekid » Tue Jul 06, 2021 3:13 pm

Hey Enzo thanks for bearing with me, here's the latest

Made the light bulb current limiter, and what I found.

Plugged in and turned on BRIGHT LIGHT 40watt bulb dead short somewhere. As stated above all the power transistors are NEW, checked before I put them in, all cement resistors checked none are open, on either board.

The mixer board was not plugged in. no DC voltages on the board.

Un plugged the Transformer, turned the unit on, bulb lit about half wattage, Measured the output from the orange wires from the transformer, 12 volts on either side of center.

22.2 volts from the red wires, either side of the center plug, course you said the voltages might be wrong. I have a 150 watt bulb would that render different results?

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Re: Peavey XR-600 400B/G

Post by Enzo » Tue Jul 06, 2021 6:51 pm

It is OK to run the power amp board with the preamp disconnected, I prefer it in fact when the power amp blows fuses. (I use the casual term "blows fuses" to mean bulb lights bright)

Power transistors new? OK, make sure none are shorted to chassis - ie an insulating wafer was left out or something.

You coculd try this: leave the red and orange wires unplugged and power up just the transformer directly - not on th bulb. Risking a fuse, but at least we could find out the real voltage the transformer makes, I suspect OK. I'd expect about 35-0-35vAC for red.

Otherwise stay on bulb. Check the main rectifiers for shorts. Check the two main rails for short to ground.

SOme amps using this board had the small "output transformer" as noted on the drawing. This amp does not have that, correct? If it doess, disconnect it.

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Re: Peavey XR-600 400B/G

Post by Chaffeekid » Wed Jul 07, 2021 3:12 pm

Latest update

CR126 in circuit with the 7815 was bad measured 14 ohms both directions it is a diode replaced it

Voltages measured with transformer unplugged from the board and unit plugged in direct. 20.5 each side of zero on orange wires

37.5 each side on red wires did not blow a fuse

Plugged in to current limiter still registers a short No voltage past the switch on the board no ac at the rectifiers, no measurable dc on the board does still blow a fuse if plugged in direct. 6amp

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Re: Peavey XR-600 400B/G

Post by Enzo » Wed Jul 07, 2021 6:57 pm

Are you sure you don't have a 400BH board instead of 400G? The 400B/G doesn't have those diodes, at least not numbered on the schematic, those are on 400BH.

How about the things I suggested in the previous post?

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Re: Peavey XR-600 400B/G

Post by Chaffeekid » Thu Jul 08, 2021 7:29 am

Yep, sure is a B/G on the solder side.

Doing a lot of reading, unplugged the high voltage (red) from the board, HEY HEY HEY 15 volts plus and minus, low voltage supply is good.

Unplugged the low voltage and just plugged in the hv and the limiter said SHORT, bright light. Unplugged the power amp transistor board, still shorted.

I have replaced the rectifiers, all four with new P600D's the filter caps are good, I suspect the Zener diodes, do you know what value they are? Whats the breakover voltage? Thanks

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Re: Peavey XR-600 400B/G

Post by Enzo » Thu Jul 08, 2021 8:30 am

What zener diodes? The 15v ones? They are not likely to blow fuses, besides, you can check them with an ohm meter.

Are either of the 50v rails shorted to ground? ANy chance the two-wire connector between main board and power transistor board is unplugged or otherwise open? Or teh diode at the power transistor board end?

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