Needing help repairing an Orion HCCA 250 Digital Reference

[Chopperbuilder]

The muting circuit on this amp is similar to the HCCA 225 but different. I pulled the other 2N5639 that is part of that circuit and checked it. It is fine. Also checked the voltage on pad 3 of the two muting transistors, voltage is -15.5v. Any idea of what else I should check?

 

[Perry Babin]

Did I miss where you said you reinstalled the muting transistors?

I thought that the input to the 5534 was constant. Is that wrong?

 

[Chopperbuilder]

That is my fault as I failed to state that I had reinstalled them after I pulled them in the beginning of this thread. I had actually reinstalled them before I started it. Sorry about that.


To be honest I'm not sure if the the input to the 5534 was constant as I'm not sure if I ever tested it after the amp output had fallen off.

 

[Perry Babin]

To get on the same page...

Post images of the waveforms on the two inputs and the output of the 5534 just before and just after the output clips. 6 images.

If the speaker output is still clipping at 10v and the rails are still well above 10v (30+v), there's no need to post photos of the output to the speaker terminals.

 

[Chopperbuilder]

Scope set at 5v/div.
The photos are of the 5534 input pins 2 and 3 and output pin 6 left to right.
First 3 are just prior to clipping, second 3 are just after clipping.

 

[Perry Babin]

Post a photo of the amp as it is/was when those photos were taken (post #45) showing the area in the attached photo clearly enough to read part numbers and the colors off of the resistors.

 

[Chopperbuilder]

Here is a couple of photos of that area.

 

[Perry Babin]

What's the value (measured) of the resistor indicated in the photo?

 

[Chopperbuilder]

It measures at 2.8 Ohms.

 

[Perry Babin]

Do all of the orange diodes that it drives read as OK?

Are all of the drivers and pre-drivers original?

 

[Chopperbuilder]

I know the diodes should be pulled from the circuit to properly check them. Is there a way to check them in circuit?


All the drivers and pre-drivers are original.

 

[Perry Babin]

You can check them on diode check. None should read open. I'd expect them to read about 0.55v when forward biased.

 

[Chopperbuilder]

That is all the drivers and pre-drivers are original except for the PS FET drivers - MPSA06's and MPSA56's.

 

[Perry Babin]

What's the resistance between the RCA shields and the non-bridging speaker wires?

If you connect a load to one channel and drive that channel hard (only needed for long enough to check with the scope), do you see any signal on the non-bridging speaker terminals?

 

[Chopperbuilder]

All the orange diodes that the resistor drives are reading between +0.65v and +0.66v.

 

[Chopperbuilder]

I'm not sure what you mean by "non-bridging speaker wires"?


This late at night I cannot hook a speaker to it. Is there something else I can use to connect a load to it?

 

[Perry Babin]

Non-bridging speaker wires are the wires that are not used when the amp is connected in bridged configuration. They go into the center of the board.

Also check the resistance from the RCA shield to the secondary center tap on the transformer.

Do you have a current limiting resistor or dummy load?

 

[Chopperbuilder]

Yes, I have a current limiting resistor I can use. As soon as my scope warms up I'll run that test.


The resistance between the RCA shields and the non-bridging speaker wires is 0.1 Ohms (my test leads are 0.1 Ohms).


Will you show me the the secondary center tap on the transformer?

 

[Chopperbuilder]

Load connected to one channel and driven hard there is no signal on the non-bridging speaker terminals.

 

[Perry Babin]

Different amp but it should be good enough. Either point is the secondary CT.