Orion HCCA 2100 no rail voltage.

[Perry Babin]

The gate voltage has to be much lower to turn the muting transistors off.

 

[Chopperbuilder]

Yes, I remember from the HCCA 225. I see that the circuit is very similar in this amp but it is laid out different.

 

[Perry Babin]

If you're going to work on a lot of these amps, you need to learn the circuits and how they work, regardless of the layout.

 

[Chopperbuilder]

That is exactly what I'm trying to do is learn the circuits and how they work.

 

[Chopperbuilder]

Schematics would be a large help.

 

[Perry Babin]

For the most part, for the old amps, you have to make them yourself or get them from someone who has taken the time to make them. Very few were distributed by the manufacturer at the time. If they were, they were faxed and some of the copies are multi-generation fax copies.

 

[Chopperbuilder]

Taken a step backwards. Pulled the muting transistors to see if the amp achieved full output. Not sure if it was at full output ( didn't have it powered on long enough to be sure) but it had significantly increased. Almost immediately the 6491 that was shorted before heated up and blew out.

Replaced it and then checked the emitter resisters they were all reading between 0.007v and 0.009v. I pulled all the output transistors on that side and checked them, they all tested good.

 

[Chopperbuilder]

With the lamp back in circuit on the red wire that feeds the audio circuit, all output transistors on that side pulled, the lamp very dimly illuminates.

 

[Perry Babin]

Do you have essentially the same DC voltage across all of the emitter resistors in that channel? The voltage across these resistors tells you where the current is flowing. That's why the higher voltage for one of the emitter resistors for one of the output transistors pointed to a problem.

 

[Chopperbuilder]

That's what I went looking for before I posted. All the output transistors on that side are still pulled out of circuit. The DC voltage across the emitter resistors is 0.000v. Before I pulled the resistors they were all between 0.007v and 0.009v.

 

[Chopperbuilder]

I'm at a loss here with this piece of junk amp. Starting to think it would better to strip it down and use it for parts.

 

[Perry Babin]

If all emitter resistors had approximately the same voltage, I'd look to see if the voltage across the 4 orange diodes near the 5534 was different from one channel to the other.

 

[Chopperbuilder]

The DC voltage across the orange diodes near the 5534 on the right side are all between +0.605v and +0.614v.

See photo for the DC voltages across the left side diodes.

 

[Chopperbuilder]

I still have all the output transistors on the left side out of circuit still, should I reinstall them?

 

[Perry Babin]

The diodes should not read as high as they are, on the left side. Lift one lead and re-check them out of the circuit. Black probe on the striped end.

 

[Chopperbuilder]

I'm not sure if I fully understand what you are wanting me to do. Are you wanting me to lift one of the leads on one the diodes and check the DC voltage across the remaining three?

 

[Perry Babin]

The diodes are small and difficult for me to hold so I only desolder one lead to check them. Do this with no power applied. Check them on diode-check and resistance.

 

[Chopperbuilder]

Had me wondering for a minute there.
They are all between +0.625v/+0.627v.

 

[Perry Babin]

Were the probes oriented the same way as when you read more than 2v across some of them?

 

[Chopperbuilder]

Not sure that I had the black probe on the striped end on all of them but at least two of them.