Crest CC2800 Help!

[Enzo]

Note Q114 is wired as the driver, while the rest of the row are all outputs in parallel. If Q114 is bad, it must be replaced. But if it is one of the rest of the row that is bad, during test, just remove it, the amp will function without it. The amp really only needs one output on the positive side and one on the negative side to function. It won;t of course put out full power, but unloaded it wonlt care, and with a speaker, just don't ask it to be loud. This is only for during repair. But running with an empty space in the row will at least allow you to determine that the rest of the circuit is functioning or not.

[pontiacpete]

That's interesting.
Can start it up without the heat sink attached in this situation?

[Enzo]

no no no, never power up an amp with the transistors off the heatsink, unless you know exactly what you are doing.

[pontiacpete]

I thought you would say that. You told me that in the past.

So to check the +/- 24 at the bridge iwth the light bulb on, I will put the transistors in that still have their legs and bolt them down to the sink and start it up.
I guess you are saying, that i should replace the whole row later on,,,

[Enzo]

You need to have a whole good row when you are done, but until then, you can run with fewer. As long as they are already out, verify none are shorted.

[pontiacpete]

With it all back together, I powered it up on the variac and the bulb.
I brought up to a little over 100vac and all I got was +/-3.2vdc throughout the increase of AC
Is the transformer not making enough AC on that winding or is the bridge rectifier having problems?

edit: I took some measurements off of the j2.
there are 4 leads off of the transformer.
1. 30vac
2. 6vac
3. 6vac
4. 10vac

[Jazz P Bass]

Not too sure how you came about those readings.
#4 should be at ground potential.
Call it common to the other three.

[pontiacpete]

Oh, duh, different ground.
I connected to ground on the main filter caps. I'll do the test again.

[pontiacpete]

Using #4 as ground, 1, 2, and 3 each about 20vac on them. THose windings are working.

But the +/- 3.2 is still on either end of the bridge,, no +/- 24 v.

[Jazz P Bass]

Not having the amp here, I have to ask.
Is there a way to disconnect the +24 & -24 where it leaves the power board?
That would give you a chance at verifying the bridge rectifier circuit.
How does the +6.2 volt look?

[pontiacpete]

THere is no way to disconnect the +/-24. THe connector from the PT comes in right next to B1 and then it's SMD from there on.

At R1 it's reading 1.6vac when brought up to 100vac.

[pontiacpete]

I thought I posted this but , guess I didn't ..

My mistake about the ground,,, so using #4 as the ground potential, pins 1-3 have about 19vac.
There is still 3.3 +/- on B1.
There's 1.6vdc on R1

[Jazz P Bass]

Something is loading it down.
So start searching.
Luckily the 24 volts is the confined to the front panel & protect schematic.
I see a coulple of regulators, transistors & caps on both rails.
See if any are shorted.

[jlatte]

It's been a while since any further comments on this thread.
I have a CC4000. Experiencing same issue except mine began with a little water exposure
which in turn somehow knocked out Thermistor R33.
I replaced this thermistor and powered the amp up with a 100watt bulb. The bulb glowed fully.

Was there any outcome to this tread or anyone interested in taking me up with any guidance.

[pontiacpete]

Sorry jlatte, that's it on this thread. I bailed on the repair.