Orion HCCA2100

[Dr Zeus]

I'm in the middle of repairing this amp's power supply section. I sort of presumed using IRF3205 fets would work for the entire amp, after all the original NDR7060 appear to be less available and rated lower. I replaced all mix-matched fets with 28x IRF3205. The amp powers will no current draw and should play. I am getting +- regulated voltage at the opAmps, and +-40v rail.

The one thing I am seeing which I feel is odd is the waveform on the PS gates. Normally I see this as +10v square or regulated, but in this amp I see a +5v wave. This picture is taken at 5V/Div and 10uS:



I was reading on the DVD and it appears the ZDs in the power supply section have something to do with how this amp produces lower and upper power ranges. Presuming the above image is normal, is there anyway other than loading the amp with subs; how I can controllable switch the powersupply into a higher output range (and perhaps see regulated +10v Waveform on the gates)?

Thanks

[Perry Babin]

The amp uses Pulse Amplitude Modulation instead of PWM. Set the 12v DC power supply voltage lower and the drive amplitude will increase.

[Dr Zeus]

OK i completely rebuilt the power supply in this amp; had it test/working out on the bench for a little while. i flipped the amp over (Right side up) and moments later it let out some dragon smoke. The amp didnt draw muchcurrent at all, and I imidiately took it off the power supply.

Here is what happened:





A good friend of mine has another HCCA 2100, so i was able to snap a photo of what its supposed to look like in working order here:

[Dr Zeus]

The left-over leads of the blown 2N5639 has a measurement of 0ohms across the middle and right legs, almost as if the 33pF ceramic cap to the right of it is shorted internally, but i believe these readings may be measuring back to one of the power supply's windings. Legs 2&3 also have 0ohms to RCA shields and non-bridging speaker terminals.

[Dr Zeus]

Well it looks like I found this one out All my fault.

Its a good thing these amps have an inner-sync which can allow the whole amp to slide out. Underneith the fan a piece of copper strand got spark-welded to a few pads near this blown transistor. Cleaned it up and no more shorts between 2&3. I do have to say though, that the way the cooling system is designed in this amp has the porential to blow bits all over the board and possibly cause this.


I dont have any 2N5639 but I have a lot of other parts. Do I have to use an N-CH Fet for this or can I use somehting like a BC140, MPSA06/56?

[Perry Babin]

It's a jfet. You have to replace it with a jfet. A j108 may work but I've never tired it.