ORION SX 2150 "of destruction" -or devistation

[Dr Zeus]

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.

[Perry Babin]

What's the signal look like on pins 9 and 10 of the 494?

If none of the outputs are shorted, you may have a shorted rail cap.

Did the rectifier read shorted 1-3 out of the board?

[Dr Zeus]

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.

[Perry Babin]

Set the vertical amp 1 click clockwise and adjust the trigger level to see if it will lock.

[Dr Zeus]

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??

[Dr Zeus]

Heres another shot of the scope w/ settings.

[Perry Babin]

There's nothing out of phase there. The scope simply wasn't triggering properly.

I don't really see anything wrong.

Reinstall the rectifiers. Connect a current limiter in series with the B+ line and measure the DC voltage across each of the emitter resistors. Do any read more than 0.000v DC?

[Dr Zeus]

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...

[Perry Babin]

Twist the transformer. It could have an intermittently shorted winding.

The 9316 is likely a date code (1993, 16th week). The rectifiers on the side of the heatsink are used to produce the drive voltage for the power supply transistors. They feed the 7815 standing near the transformer.

[Dr Zeus]

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.