CS400 PowerBoard - 1979

[Hans]

I've got a broken down CS400 amp and have already got the right schematics, thanks to Mrs. Google who's being a great help in this matter.

The power board, possibly even both, appears to be broken, the fuse had been blown, at least one of the .33 Ohm resistors become quite hot. I'd driving the amp for test purposes through a simple bulb to prevent further damage.

I have a few questions: There is a red and brown cable running to the driver board. A "device", fixed to the cooler, is connected there as well. This "device" is broken in pieces, what could that be ?

There are transistors installed "2N3773" and "MJ15020", the schematics refer to 6357 or 6344, are these replacements ?

[pontiacpete]

can you post the schematic?

[Jazz P Bass]

Peavey CS400 Schematic

Here it is.

[Hans]

Schematic

Here it is.

No, this is not the one I have, my amp has only NPN transistors on the power board. I'll upload the schematics later this week since I'm on business trip.

[Hans]

The "device" I'm referring to appears to be "CR12", this looks like a few diodes plus a resistor. It is connected to the power board but the connector itself runs to the driver board with red and brown wires. However, I've already got one channel to work fine, the other one has this broken "diode - transistor" thing which I don't know what it is and what is does - or should do.

[olddawg]

It's been a long time since I have seen one of these and they changed over the years. The device you are talking about could be a thermistor on the heat sink or a stacked diode. If it is a stacked diode it will appear on the schematic as several diode junctions in series and can be substituted by rectifier diodes in series using the the number of junctions in the schematic. You can call Peavey you know. They are usually very helpful, even with old stuff, and probably still stock the part.

[Hans]

Thanks, I'll contact Peavey, let's see whether they can help.

[Enzo]

Jazz, that is the newer "wind tunnel" style CS400. He has the original one.

Go to the Schematics Request section of this forum, and one of the sticky threads near the top is the Peavey semiconductor crossreference. You can look up those SJ6344 or SJ6357 types and find their MJ150xx equivalents.

CR12 is a dual diode (two junctions in series), the resistor is a separate part. Those dual diodes are Peavey type 13886. You can get them direct from Peavey, I do. You could screw around coming up with something to put in their place, but it is so much easier to just use the exact part in the first place.

I'll add the schematic here below.

The dual diode is part of the bias circuit, it is mounted on the heatsink to thermally track. During test, you can replace it with a piece of wire - yes, short right across it. That will let you determine if anything else is bad. The resulot of deleting that dual diode will be increasede crossover distortion but the amp channel will also run cooler.

The two power amp channels are independent, and you can disable either one by pulling the four-wire molex connector to the main power transistor board.

[Hans]

Thanks Enzo, thats quite valuable info ! The schematics are the right ones, thanks as well. Let you know when the second channel works too.

[Enzo]

Aha, I am not going crazy, we DO have two threads going for this repair. Let us pick one and let the other one die.

[Jazz P Bass]

Jazz, that is the newer "wind tunnel" style CS400. He has the original one.

O/k.
I'll bite.
What the heck is a 'wind tunnel' amp?

[52 Bill]

It means that the amp is aerodynamically stable up to its full rated output!

Enzo's referring to the heatsink design. It has one of those fan cooled "wind tunnel" heatsinks.

[Enzo]

The original CS400 and CS800 had solid metal fronts. There was a fan in the rear, and vent holes on the lid to allow air flow.


Newer designs had the large vent grille on the front panel, and the fan on the rear. The heat sinks formed a tunnel through the middle of the amp. COmpare the front panel pcture in these owner manuals.

Original
http://www.peavey.com/assets/literat...0_c_series.pdf

Extra Crispy... I mean wind tunnel
http://www.peavey.com/assets/literat...s/80300990.pdf

[Enzo]

The original CS400 and CS800 had solid metal fronts. There was a fan in the rear, and vent holes on the lid to allow air flow.


Newer designs had the large vent grille on the front panel, and the fan on the rear. The heat sinks formed a tunnel through the middle of the amp. COmpare the front panel pcture in these owner manuals.

Original
http://www.peavey.com/assets/literat...0_c_series.pdf

Extra Crispy... I mean wind tunnel
http://www.peavey.com/assets/literat...s/80300990.pdf

[Jazz P Bass]

Gotcha on the wind tunnel.
Thanks.
I new there was something familiar there.
I worked on one 2 weeks ago.