Another Orion stumper for me. This amp powers with 0.6A idle and has good +- voltage everywhere, almost. It will sometimes play a little out of the left channel at first power-up, but starts to get clamped down and goes mute. The right channel plays nothing.
Theres an opamp in the middle of the board that I replaced, because I was finding close to regulated supply voltage not only on the power pins, but also on the output pins. I replaced the JRC4562D with a spare TL072. I notice the DC voltage on output pins climbs as the amp stays powered on for a few seconds. All input pins are at 0vDC. Regulated voltage is about +-14. All other opamps are either at close to 0vDC or +-14vDC on pins, IE correct.
All diodes seem to be testing OK in circuit. Same for the MPSA06/56.
This amp is Orion built but not sure how similar this is to other more popular Orions. Its simplified compared to some of the SX line I've been working on. This one was built in 1997. For BestBuy is my guess.
Thanks ahead, if help is available.
Pics next post.
Theres an opamp in the middle of the board that I replaced, because I was finding close to regulated supply voltage not only on the power pins, but also on the output pins. I replaced the JRC4562D with a spare TL072. I notice the DC voltage on output pins climbs as the amp stays powered on for a few seconds. All input pins are at 0vDC. Regulated voltage is about +-14. All other opamps are either at close to 0vDC or +-14vDC on pins, IE correct.
All diodes seem to be testing OK in circuit. Same for the MPSA06/56.
This amp is Orion built but not sure how similar this is to other more popular Orions. Its simplified compared to some of the SX line I've been working on. This one was built in 1997. For BestBuy is my guess.
Thanks ahead, if help is available.
Pics next post.
Last edited:
Does it use the same jfet muting that the Orion's use?
Is there any audio on the outputs of any of the op-amps in the preamp section or the input or output of the TL072?
Is there any audio on the outputs of any of the op-amps in the preamp section or the input or output of the TL072?
The opamps in the pre-amp section all have audio on their pins, of course depending on crossover settings. I'm getting audio on pins 2 and 5 of the center opAmp, thats U3. Those are linked back to the preamps from L&R channel inputs.
Here is U3 meter set to vDC
1: 0.59
2: 0 (Audio from Right RCA)
3: 0
4: -14.71
5: 0 (Audio from Left RCA)
6: 0
7: 0.381
8: 14.83
Here is same, U3 with meter set to vAC
1: 14.3 (SQUARE WAVE)
2: 0.286 (Audio)
3: 0
4: 0
5: 0.156 (Audio)
6: 0
7: 14.34 (SQUARE WAVE)
8: 0
Most of the transistors are MPSA06/56 transistors
Q33/Q34 and Q15 have 2N5639. Top left, and bottom left.
I thought it was really weird to see a square wave on output pins of the opamp. When I first turn on the amp, the signal actually starts as a audio sine wave and then within two seconds rises to a completely clipped out square wave - pins 1 and 7.
Here is U3 meter set to vDC
1: 0.59
2: 0 (Audio from Right RCA)
3: 0
4: -14.71
5: 0 (Audio from Left RCA)
6: 0
7: 0.381
8: 14.83
Here is same, U3 with meter set to vAC
1: 14.3 (SQUARE WAVE)
2: 0.286 (Audio)
3: 0
4: 0
5: 0.156 (Audio)
6: 0
7: 14.34 (SQUARE WAVE)
8: 0
Most of the transistors are MPSA06/56 transistors
Q33/Q34 and Q15 have 2N5639. Top left, and bottom left.
I thought it was really weird to see a square wave on output pins of the opamp. When I first turn on the amp, the signal actually starts as a audio sine wave and then within two seconds rises to a completely clipped out square wave - pins 1 and 7.
What's the DC voltage on pin 3 of the jfets?
I wouldn't expect to see a square wave unless it was inside the feedback loop and part of the loop was disabled or missing.
I wouldn't expect to see a square wave unless it was inside the feedback loop and part of the loop was disabled or missing.
Rail voltage is +-36.7vDC
DC referencing secondary center tap
Q33: 0, 0, -32
Q34: 0, 0, -32
Q15: -32, 0, -36.4
DC referencing secondary center tap
Q33: 0, 0, -32
Q34: 0, 0, -32
Q15: -32, 0, -36.4
Yes there is audio signal on pin 1 both q33/34. Pin 2 is connected directly to rca shields and non bridging terminals. <1 ohm. 180 ohms to amp ground.
Mpsa56. I removed both but amp didn’t work any better. I forgot but the ps may not have even powered up as I can’t recall.
I probably made an error here but this is very close. Red lines show all points which have a square wave on them. On Q25-Q28 I have 0, -, & +. That’s rail voltage.
Attachments
Last edited:
Are you sure that those 4 transistors don't have open junctions?
It's odd that it could produce audio and then go mute.
If you chill those 4 transistors, does audio come back.
Re-check. I'd expect rail voltage on the collectors of all 4 of those transistors.
What are the part numbers on those 4 transistors?
It's odd that it could produce audio and then go mute.
If you chill those 4 transistors, does audio come back.
Re-check. I'd expect rail voltage on the collectors of all 4 of those transistors.
What are the part numbers on those 4 transistors?
Check the resistors connected to the collector and emitter of those 4 transistors to confirm that they're within tolerance.
Even being class B, it should not have this distortion.
Was the original 4562D defective?
Even being class B, it should not have this distortion.
Was the original 4562D defective?
I put the 4562D back into circuit, pulled out the TL072. That wasn't the problem.
Resistors are all checking in-circuit. I pull a few of them that were suspicious and they're OK lifted. I don't think there is much more to check. This amp is using the suspect looking Orion green/grey/blue resistors, but they're checking out fine.
I'm beginning to think that this is OK. At higher input/gain the notch is not there at all. Its only at very very low input it is seen.
Resistors are all checking in-circuit. I pull a few of them that were suspicious and they're OK lifted. I don't think there is much more to check. This amp is using the suspect looking Orion green/grey/blue resistors, but they're checking out fine.
I'm beginning to think that this is OK. At higher input/gain the notch is not there at all. Its only at very very low input it is seen.