Orion 2250sx

[RockfordFIx]

I got a orion 2250sx that will not power up. Originally I checked the outputs and powersupply for defective components and it looked good. I applied positive and negative no remote yet. And a tantalum cap exploded on pin 5 of one of the optocouplers. No need for coffee anymore at that point haha. I replaced the cap and tried again cap did not pop. Powersupplies both had ~14v but no rail voltage activation. LEDS were found to shorted cause of the leads and on broken. Pretty sure that's not my issue. Continuity checked the spier sensor to make sure the y were not issue. And both read short and I am assuming they open up under high temp. From my reading the second set of recitifiers feed the 7815 voltage and that feeds the tl494 is this correct because I have little to nothing divinely not 14v. Any help I will order some optocouplers dice I don't have any

 

[Perry Babin]

For the opto-coupler with 12v on pin 5, what's the DC voltage measured directly across pins 1 and 2 (black probe on pin 2)?

Across pins 4 and 5 (black on 4)?

 

[RockfordFIx]

Opto w/ 12v on pin 5

Across 1 & 2 black on 2 = 1.152v
Across 4 & 5 black on 4 = 0.162v

1= 1.150v
2= 0v
3= 0v
4= 13.43v
5= 13.42v
6= 14.07v

Optocoupler 2

1= 1.175v
2= 0v
3= 0v
4= 0v
5= 0v
6= 0.499v

 

[Perry Babin]

Pin 4 drives the base of an MPSA06. The emitter of the A06 drives the 494 via the thermostat. Is either the A06 or the thermostat open?

 

[RockfordFIx]

I will pull the a06 tonight. Thermostat switches on the bottom of board both read short or closed. If the a06 is okay are u leaning toward the 494?

 

[RockfordFIx]

I pulled the A06 and it was in fact open so I replaced and powered unit. Same out come no rail activation.

 

[Perry Babin]

Do you now have about 12v on its emitter and on pin 12 of the 494?

 

[RockfordFIx]

I don't have 12v on the emitter nor the 494. I have 13.5v on the collector and base.

 

[Perry Babin]

It's open again. Is there a short to ground from pin 12 to ground?

 

[RockfordFIx]

I removed the A06 again and discovered that the base to collector was shorted. I replaced it again and this time it smoked. Do you have a schematic for the powersupply on this unit.

 

[RockfordFIx]

Yes pin 12 is short to ground. I will remove the 494 and see if it still shor to ground

 

[RockfordFIx]

I removed the if 494 and pin12 is still shorted to ground... working my way back.

 

[RockfordFIx]

Do you have a pic of the powersupply where the rectifier are. It's 2 rectifier and 2 2n2488?

 

[Perry Babin]

Post a photo of the area you need to see.

 

[RockfordFIx]

Started chasing short but ran out of time I know I remove the rectifier and the 2488 but make sure I didn't install in wrong direction

 

[RockfordFIx]

Perry after removing a few components tracing back the short I realized I missed a small trace that did follow the thermostat circuit. Here is pic of the shorted caps cause g the bcc pin to be shorted to ground.

 

[RockfordFIx]

Pic of shorted caps causing pin 12 to be shorted to ground

 

[RockfordFIx]

Perry the amp powered up just fine and produced audio. What I did notice is one powersupply is running on the rail voltage. One side is producing 58v and the other channel is get 30 volts. Looks as this powersupply in question has had issues as there are brown resistors. This was probably the original problem now that I have treated the symptoms

 

[Perry Babin]

The rail voltage is determined by the zeners that drive the base of the 6488. Check the zeners in the low channel.

 

[RockfordFIx]

Do you recall what the rail voltage should be for this amp