ORION SX 2150 "of destruction" -or devistation

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Devistation because this amp has surely seen some better days. Aside from having the internal wires cut and terminals missing, the sync is also missing the bottoms and the sides. I also salvaged one of the output drivers from this amp to get an SX2250 working properly for a collector.

Needless to say I am ready to make a decent effort in repairing this amp, as this is one that personally now own.

A small handfull of the transistors were damaged during disasembly by myself; not really knowing that these Orions could pose such a disasembly issue; most notible the three 6491 units in the top left of the first photo. They just split in half! Also one of the rectifiers (9316) split in half as well. One of the power supply fets also split and I cut it off the board. I left one leg of the destroyed transsitors attached so that I could remember exactly what they were.

When I got the amp it was missing two transistors to the left of the top row of outputs.

At first I could not get this amplifier to accept power. It would just moan and squeeze on the juice until my 15a breaker tripped. On the bottom of the PCB are two large rectifiers which I pulled off the board while not knowing they were rectifiers (1-3 shorted). After which, the amp will accept power and actually try to power up.

This amp has a TL494:
1: 0.002
2: 0.034
3: 0.035
4: 0.042
5: 1.535
6: 3.456
7: 0.001
8: 10.00
9: 4.17
10: 4.17
11: 10.00
12: 10.00
13: 5.00
14: 5.00
15: 0.035
16: 0.002



Scope set to 5v/Div. Time/Div cant focus the signal - its a variable signal.


I'm gonna try removing all the power fets to hopefully get a better reading on the TL494.
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The large rectifiers underneith are within tollerance off the board.

Non of the outputs seem to be shorted. At least while on the PCB none of the large caps are coming up shorted.

TL494 pins 9 & 10 measuring like this on the scope. Time/div adjustment can not 'lock' on whatever is happening in-between the lines.

Not sure what vertical amp is on this scope. I normally leave SYNC set to HFrej, but tried it set to AC and got this on the TL494 Pin 9&10:


Also under the new setting on the scope, the power supply fets leg 1 are showing this. It looks like something is out of phase??

I'm not sure what I just did exactly; or if anything. The amp powers up and is stable with a 5A fuse now; however after about a minute the power supply fets start to get warm to the touch - but not overheating. This is all without the 9316 rectifier because that one got damaged.

One Speaker terminal output has 0.068vDC and the other has 0vDC.
Emmitter resistors all read 0.000vDC

Hmmm... This sounds surprisingly OK for the moment. I'll run it through a series of other tests to see what is what...
I'll have to try the transformer twist later tonight. Hopefully that is ok. If it is defective can they be replaced or repaired? There are no open cuts, breaks, or detached coil wires, however when the amp has power I can almost hear a little squeeking/squeeling possibly comeing from the coil.

I get positive and negative voltages at the outputs, +/- 22vDC. That seems a little low to me but I dont know how this amp steps up. Both legs 1 and 3 of the outputs are seeing this voltage level.

The opamps are not getting any voltage; tested referencing both amp ground and non-bridging terminals yields nothing. Something is not giving them any power I believe. Could it be the rects or the two missing LM transistors?

Speaker terminal outputs do not have any DC across them referencing non-bridging terminals. I'll test again measuring amp ground but I think its zero also.
The opAmps are getting +- 13vDC.

The LM317 near the shorted cap is still getting a little hot but not like before. Someone previously replaced the 5.6 ohm resistor for a 1.0 ohm coming off of this LM317's 3rd leg, but I changed it back to as close as I had available - a 4.7ohm resistor.

Is 4.7 ohms too low for the LM317? 4.7 is more common than 5.6.

Picture courtesy of Perry.

The cap that was shorted is the one closest to the LM337.


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The 4.7 ohm shouldn't be causing it to run hotter. Although resistors are sometimes used to drop a few volts before the regulator (so the regulator won't have to dissipate as much heat), I don't think that's the purpose of the resistor here. Connect the 1 ohm that you removed from the amp in series with the 4.7. If the temperature of the regulator decreases, you know it's the 4.7 that's causing it to run hot. If the regulator continues to run hot, you know that there's another cause.

The 5543 op-amps have a 2.7 ohm resistor in series with their power supply pins. Do they all have the same voltage drop across them?

Are they all within tolerance?

I'm assuming that these regulators feed the 5534s and the other two regs feed the rest of the op-amps. Correct me if that's wrong.
I'll check those out.

Can I use MPSU06/56 for drivers in this amp? MPSU07/57 drivers are impossible to find, and Central denied my samples request for their equivelant part. Central-Semi wanted me to buy them in quantities of 100 at $2.50 a piece.

I need 2 of each, but can maybe get by with just one of each. This amp was previously used to correct an Orion 2250 which had a failed MPSU07.
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