Help, Mr. Perry Babin !! Orion 225 HCCA trouble

[Yusef71]

Dear Sir, I recently did some repair work on an Orion 225 HCCA amplifier. Replaced some shorted output transistors and one audio Op-amp, however now I'm getting distortion coming from the right channel. Could another audio Op-amp be at fault, and if so, which one ? I replaced the first audio Op-amp chip in the center of the circuit board right below the two muting transistors. Any help would be greatly appreciated !!

[Dr Zeus]

You say the outputs were replaced? Did you check the drivers?

You may have the same thing I had in this thread here: Orion 2250 Gen II output help

[Perry Babin]

Which revision/gen is the amp?

[Yusef71]

I believe it might be a 2nd generation version, I'm not sure. However another user on this forum posted pics that are identical to what I have' Here are his pics.

[Perry Babin]

Do you have a scope?

Is this the channel with the yellow speaker wire?

There are several 75 ohm resistors that tend to open or go out of tolerance. You should check any that are discolored.

The drivers are always suspect but they generally short causing the amp to draw excessive current.

[Yusef71]

No, unfortunately, I don't have oscilloscope, and yes, it is the yellow wire that corresponds to the right channel. I've made a visual check of some resistors, and there is indeed a few that show discoloration. What color are the 75 Ohm transistors in question ? For thoroughness sake, where on the circuit board and what identifying numbers do the driver transistors have. I believe the amp might indeed be drawing excessive current as the toroidal transformer heats up, even when there load is applied to the amp.

[Perry Babin]

See attached image for the 75 ohm resistors.

The drivers will be MPSA06s and MPSA56s.

Do you have an amp meter on your power supply?

Do you have a current limiting resistor that you can insert in the B+ line.

[Yusef71]

O.K., now the amp will not power up. It only turns on for a few seconds or a minute at the most. I checked pin No. 12 on TL747, it shows 13.9 V when the remote signal is applied. Also checked pin No. 9 and 10. They both show 5.4 V. There is no power, positive or negative, on the large emitter resistors. What could the problem be now ??

[Perry Babin]

What is the DC voltage on the gate legs of the power supply FETs?

[Yusef71]

Originally Posted by Yusef71

O.K., now the amp will not power up. It only turns on for a few seconds or a minute at the most. I checked pin No. 12 on TL747, it shows 13.9 V when the remote signal is applied. Also checked pin No. 9 and 10. They both show 5.4 V. There is no power, positive or negative, on the large emitter resistors. What could the problem be now ??

Correction, that's the TL474, my bad