CS-400 84B Schematic

[albertm]

Hi,
Could someone post a schematic for a Peavey CS-400 from 1984? I've seen other schematics in this area but they are either too old or too new. My CS-400 output boards have all NPN transistors (6433 drivers & 6357 output transistors) and no protective thing on the output.
Thanks,
Albert

[The Dude]

This should be close:

https://www.audioservicemanuals.com/...chematic-1.jpg

[Enzo]

All the old CS series are quasi-complementary and so have all NPN outputs.

Here is a pdf from the factory.

[albertm]

Your schematics seem to be too different: none of the driver or output transistors are the same and my output board is one piece - not split into positive and negative boards. I found three shorted output transistors on one of my output boards and I fear I should check some things before trying the new transistors even though I'm not sure what exactly to check.

I'm thinking I might want to check the transistor biasing since it might turn transistors on when they shouldn't be and the + & - rails will end up fighting each other through the output transistors and blow them up.

Thanks for your advice I found on other posts; it helped me get this far.

Albert

[Enzo]

First off, the schematic says 66161 transistors, which was an RCA 1B05. Yours has Motorola 6357 (actually SJ6357, though they often do not print the SJ on the part). But they are equivalent. You DO NOT want to mix the RCA and Moto parts, as they won't share current well, but you can use either type in there.

The RCA parts are long gone anyway. I have a few good ones I pulled when converting to Moto on some amps. The modern parts are all Moto. The 6357 is a Moto MJ15003, the 6343 is an MJ15024. An MJ15024 will work fine as a 6357 too.

The SJE6018 is really an MJE340, and the SJE6019 is really an MJE350. There are lots of alternative semiconductors. What matters is the circuit.

Aside from the numbers, does the circuit look the same?

Look up and make a "light bulb limiter". Very simple thing. Plug the amp into it and use it until it seems not to want to pop fuses or burn up.

ANY time a power transistor burns, always check all associated resistors. In your case likely the 0.33 ohm ballast resistors can be burnt open by a shorted transistor. Often as not, when the outputs short, nothing else is damaged. Win win.

SO how about some photos of the boards? The output protection triac is right on the output board, the board with the speaker connections. They are not up on the power transistor board.

The little card with the amp circuits that connect to the power transistors, is it ALL transistors? Or is there an 8-leg IC on it? Or maybe two?

The bias is not adjustable, it is either OK or gone completely.

How did you determine 1984? The CS400C is from 1979.

I will post the C version here and also the semiconductor crossreference.

[albertm]

I attached photos.

1984:
* 84B on the sticker on the bottom,
* https://secure.peavey.com/serial-lookup/ SN 4A-01874481 says 1984,
* output transistor date codes around 8413 and most other components too.

There are two 8-pin ICs on the board that doesn't have the power transistors on it.

Bias: I meant checking the other components. Don't caps go bad and cause problems?

I check the resistors now, like you recommended.

Thanks,
Albert

[albertm]

I found 1 open 0.33 ohm, 10W resistor.

[Enzo]

No doubt that resistor was associated with one of th shorted transistors. OK 1984 it is, which means it really should be a CS400C. We have posted both A and C versions.Looking at your photos, it looks like a C to me. The center picture I can see the power parts board, and just at the right edge, I see the gap between it and the other channel.

I can't quite read the parts. The 6357 are the outputs and the 6343 are drivers. If the drivers are OK, that is good for you. If you had to replace a driver, then the predriver is likely stressed, even if it checks OK. That is the 6018/6019.. Theuy rarely fail, but the two seriesed dual diodes are your bias circuit. One is clamped to the predriver on the small card, the other is up on the heat sink and connects via wires to the card. If either opens, then both sides of the outputs turn on hard. If one shorts, the am actually runs cooler but with increased crossover distortion.

Those are the 13886 diodes they used a lot in amps. It is dual inside so it has twice the voltage drop across it.

[albertm]

Enzo, I get "Invalid File Specified: when I try to read PV CS400 c.pdf (your file attached to your post at 5:14AM).

The drivers seem to be OK - no short from rails to output with them in as opposed to some of the output transistors.

Thanks,
Albert

[Enzo]

Hey, I get that too, try this one:

[Enzo]

Testing drivers. Pretty much any transistor, has three legs and are any two shorted together? And of course if not thayt, you have the diode test.

[albertm]

Enzo, I could download your new file but Adobe Reader says, "The root object is missing or invalid."

Albert

[Jazz P Bass]

He reposted it: https://music-electronics-forum.com/...etch?id=956365

[albertm]

Neither Firefox nor Adobe Reader can open the latest version of the PDF that Enzo reposted. I found it at https://elektrotanya.com/peavey_cs-4...wnload.html#dl

And this looks like what I'm working with. I thought I didn't have the CS400C because I didn't realize where the SAC187 was and thought it wasn't in mine.

Thanks,
Albert

[Enzo]

Can you open the semiconductor cross ref I posted?