Peavey CS800H Buzzing

[JP-Stereo]

Hi, i've read a few threads and i know that some people here seem to know a lot on Peavey's amp, so i register to get in.

I have one of the latest model of the CS800 it's the H version.
Wind tunnel, single PC Board and surface mount components.

The amp was working but suddently begin to "hiss ot buzz" at a loud enough level to be very annoying on both channel.
A kind of mid pitch buzz between a hiss and 60hz noise with weird "shortwave like" sound on the background.
And it was also doing a big tumb at power off.

Looking around, each amp channel have it's own dedicated power supply.
Tracing the signal, the noise appear to be from the amp circuit, barerly detectable in the pream/crossover section with a tracer.
The only common link between the Amps is the bias supply, 2 regulators for +15 and -15 dc and one for a +5v.
So i changed all the big caps on the power supply and the 3 bias regulators and their caps too.

When i powerd the unit back, i heard a buzz in the circuit and the breaker tripped.

I've remove the crowbar triac and this wat i see:

TR5
Pin 1+ and 2- = 440k
Pin 1- and 2+ = 36meg
Both position if i short pin 3 to pin 2 = between 78 Ohm

TR6
Pin 1+ and 2- = 0.647 meg
Pin 1- and 2+ = 36meg
Both position if i short pin 3 to pin 2 = between 82 Ohm


Both look suspicious to me regarding the first reading...
Is it OK or they are done ?

Thanks

[JP-Stereo]

Correction: I've found that if i clip the DVM on Pin1+ ans Pin2- at first it gave a "low reading" in the x00k-ohm.
If i short the Pin3 to Pin2 = Pin1 to Pin2 go around 80 Ohms.
After Pin3 to Pin2 is opened the Pin1- to Pin2+ reading go to a very high reading of around 40 meg-Ohm
But the Pin1+ to Pin2-+ never go over the initial reading of a X00 k-ohm..

Both act the same.

[JP-Stereo]

The Triacs are SAC187.
Doesn't read quite ok but both are near identical ???

[Helmholtz]

Need to see a schematic.

[JP-Stereo]

Hi, file too big to upload here.
What you suggest.
PM me your e-mail ?

Thanks

[JP-Stereo]

1283 kb since it's a protected PDF i cannot extract just the drawings...

[JP-Stereo]

So are these SAC187 alive or failing ???

About 500k of load on the outputs is not enough to choke them or produce any overheating...

All outputs test OK on the diode check test.
The resistors are on value.
The diode are OK too.

What else beside there SAC187 may have tripped the beaker ?

[Helmholtz]

Did you disconnect the speakers?
Do you see DCV at the output (before the relay) with the Triac(s) disconnected?

[Helmholtz]

Maybe some useful info contained here: https://music-electronics-forum.com/...0-blowing-fuse

[The Dude]

FYI: You can leave the triacs temporarily disconnected for troubleshooting purposes. They are only there for speaker protection. The caveat is that, since you no longer have DC/speaker protection, do not hook up a load until you verify that there is no DC on the output.

[JP-Stereo]

Since i disassembled the board and the heat sinks to test the output, i did not turn it on yet.
Before changing the power supply caps and the bias regulators, there was no DC on the speaker output, but the noise was present.
Maybe without bias or with partial bias the output were not active ?

But after the PS recap and the bias reg swap, it blow the breaker before coming alive.

Yes i disconnect the speaker and from now on will not reconnect a speaker unless absolutly certain that no DC is present at the speaker.

Next step is reassembling without the triacs and try again with a 100w bulb in serie with the LINE.
Maybe powering the frame/preamp without powering the amps module first, each are feed separatly by a molex connector so i figure it's an option.

[JP-Stereo]

I am still bugged about the SAC187.
The test procedures state that the Off reading should be over 1 megohm.
But i have an anode to cathode reading of around 500k on both triacs...

[JP-Stereo]

To make things weirer, look at what is driving the SAC187 :



A SBS14

A silicone bidirectional switch (Diode Thyristor)

How do we test that thing ?

[Helmholtz]

I am still bugged about the SAC187.
The test procedures state that the Off reading should be over 1 megohm.
But i have an anode to cathode reading of around 500k on both triacs...

I wouldn't worry about a factor of two. A 500k load will not have any effect on the amp.

[Helmholtz]

A SBS14

A silicone bidirectional switch (Diode Thyristor)

How do we test that thing ?

The SBS won't conduct below 8V, so you can't test it with an Ohmmeter (except for short).

Why do you suspect the crowbar circuit?