Again needing help fixing Orion HCCA 225 Digital Reference

[Perry Babin]

Black meter probe on RCA shields or one of the non-bridging speaker wires for all.

The center legs or the tabs of the rectifiers will have rail voltage.

Pins 4 and 8 on the op-amps are regulated voltage. All should read the same so only post the voltage you read on any of the op-amps.

 

[Chopperbuilder]

First, thank you for the guidance. Once I started testing, the positive and negative parts of the test became obviously clear.


Rail voltage is: +21.5v, -21.5v
op-amp regulated voltage is: +14.10v, -13.85v they all had the same reading.

 

[Perry Babin]

What is the 12v supply voltage at the amp with the amp on?

Do you have a way to play a test tone (100Hz?) through the amp?

 

[Chopperbuilder]

The supply voltage at the amp with amp on is: 12.13v
Yes, I do have a way to play a 100Hz test tone through the amp.

 

[Perry Babin]

Can you get more DC input voltage? 13.5v?

If not...
Gain at max
Both muting transistors out
Drive a test tone at level that will produce about 10v at the speaker wires.
Confirm that both channels are relatively close.

Reinstall ONE muting transistor and after leg 3 goes the lowest, drive the same signal into the amp.
What is the difference in the two channels?

 

[Chopperbuilder]

No, I have no way of getting more DC input voltage. A 12 volt power supply is all I have.

Both muting resistors out and driving a test tone as close to 10v at the speaker wires as I could get, yielded the following results:
Right channel - 12.85v
Left channel - 11.62v


Do you still want me to proceed with reinstalling one muting resistor and performing that test?

 

[Perry Babin]

Yes. Those are for reference. I want to confirm that the muting circuit is partially engaged. That's the next test.

 

[Chopperbuilder]

The transistors I have circled in the photo are all new. I replaced them back when you help me with repairing it the first time. Is that a possibility as to why we have almost a 1.25v difference between the two channels?

 

[Perry Babin]

That's less than 1dB. That's inaudible in most all situations, especially in a car.

Those transistors have nothing to do with the overall gain of the amplifier.

 

[Chopperbuilder]

I reinstalled the muting transistor circled in the pic. After approximately 20 minutes the third leg voltage peeked at -13.5v.
The test results were as follows:
Right channel 12.83v
Left channel 11.63v

 

[Perry Babin]

Retest but this time, look at the time it takes to get to very near the reference voltages. It should only take 5 seconds(?) to get to where the muting transistor has essentially no effect on the audio level.

 

[Chopperbuilder]

I tested twice. The first test it took a more than a minute( the amp had been sitting since the previous tests). I let the amp sit for 5 min and retested it and it took 50 seconds.

 

[Perry Babin]

Is the capacitor that you replaced near the transformer still out?

 

[Chopperbuilder]

No it is not still out.

 

[Perry Babin]

Remove the transistor that is next to it.

Does that change the mute delay? Removing the transistor will increase the time to regain mute mode.

 

[Chopperbuilder]

I removed the transistor next to it. I'm assuming by asking me if it changes the mute delay, you the meant for me then to re-run the tone output test...

I ran it three times with the following results:
1st test -55 seconds
2nd test - 1 minute 45 seconds
3rd test - 1 minute 15 seconds

 

[Perry Babin]

Do you have any spare resistors 47k to 100k that you could connect across the 221k resistor?

Did you smell anything that smelled like antifreeze when you initially replaced the mute delay cap (near the transformer)?

 

[Chopperbuilder]

I don't have any spare resistors in that range but I can pick up a couple tomorrow.

I did not notice anything that smelled like antifreeze when I replaced the mute delay cap.

 

[Perry Babin]

I can't guarantee that it's going to tell us anything so don't go out of your way to get them.

 

[Chopperbuilder]

Okay. So what's next?