Needing help repairing an Orion HCCA 250 Digital Reference

[Chopperbuilder]

Resistance from the RCA shield to the secondary center tap on the transformer is 0.1 Ohms.

 

[Perry Babin]

To confirm, both channels are doing the same thing. Is that right?

 

[Chopperbuilder]

Yes, they are both distorted. The distortion is a little worse on the left channel than the right channel.

 

[Perry Babin]

I didn't see it earlier but if the photo you posted was of your board, as it is now, there are missing drivers.

 

[Chopperbuilder]

That is how the board is now. I completely missed it too. Good eye! I have some of those drivers going to install them now.

 

[Chopperbuilder]

That solved the problem. Amp is now outputting a good clean single with muting transistors back in circuit. Thank you once again for your help Perry.

 

[Chopperbuilder]

I may have spoke to soon on that. Running some tests to give you more accurate information on exactly what it is doing.



I did note that the two voltage regulators I had circled in the photo in post #7 are still heating up fairly rapidly. If that is actually abnormal for this amp? I have not seen others of similar design do that.

 

[Chopperbuilder]

Amp was working great for about 20 minutes, then a loud popping sound started coming through the left channel (right channel was not popping but cutting out), then the amp shut down. I then hooked a speaker to only the left channel and the same thing happened. Then did the same with the right channel and the sound would start cutting out after about 20 minutes of play but the amp did not shut down.

As this was happening I was looking for a component that was getting hot and found the driver circled in the attached photo is getting very hot. Do you recommend I pull the driver and check it or is there something else I should look at first?

 

[Perry Babin]

I don't see a circle.

This amp doesn't have much protection. What was shutting down? Thermal, over-current?

Was the muting engaging (mute drive on leg 3 going back to ground)?

 

[Chopperbuilder]

Sorry the photo didn't save the first time.

 

[Chopperbuilder]

I didn't check to see. Started looking for components that were getting hot.

 

[Perry Babin]

Are any of the output transistors on that side of the board leaky or shorted from the base to their collector or emitter?

 

[Chopperbuilder]

I will check them although there shouldn't be as they are all brand new.

 

[Chopperbuilder]

All the output transistors on that side of the board check good from the base to their collector or emitter.

 

[Perry Babin]

When you stated that it was producing clean audio, did you confirm that with your scope?

Those transistors (assuming that they're the drivers, not the pre-drivers only drive the outputs. There aren't any other components, that I know of that could cause a driver to heat up. Is there possibly a solder bridge?

Confirm that the emitter of that transistor drives the bases of 1/2 of the outputs on that side of the board.

 

[Chopperbuilder]

Yes, I did check it with my scope but only for a few minutes.

 

[Chopperbuilder]

Those transistors are MPSU07 and MPSU57. That particular one is a MPSU57. The emitter trace leads to a film capacitor, from there to a resistor, from that to the trace that feeds the collectors of the output transistors.

 

[Chopperbuilder]

I could find no solder bridges.

 

[Chopperbuilder]

Assuming that the pin out I found for the MPSU57 is correct (see yellow arrow pointing to what it said is the emitter leg in the attached photo). Also pointed out the film capacitor, resistor and trace I mentioned in post #77.

 

[Perry Babin]

Is it the circled transistor in the diagram?