Orion 2250sx

[Perry Babin]

No but ±58 wouldn't be far from the right voltage. I always wondered how they got away with using rail voltage greater than what the outputs were rated to withstand.

 

[RockfordFIx]

Perry I made a mistake taking a voltage reading from the red and black wires on one channel I get 101volts and 61volts on the other.
Black on ground red on first set center tap.
1st pws= 9v
2nd pws= 30v

 

[RockfordFIx]

That plus the caps are rated for 63v and 50volts talk about pushing it

 

[RockfordFIx]

The zeners check out good what components are before that could. Whatever is causing the issues causes the off 3205's to warm up quick

 

[RockfordFIx]

Perry what is the second optocoupler for? I have now seemed to have lost second rail voltage

 

[Perry Babin]

The second opto-coupler is for muting.

The power supply FETs will heat more quickly, especially at low power because the supply is Pulse Amplitude Modulation, not PWM.

 

[RockfordFIx]

Where does the secondary winding voltage come from? Sorry for stupid question. Trying to find the rail voltage for the other half the board

 

[RockfordFIx]

I was able to stabilize the powersupply from overheating the FETS at idle. I replaced the a06 and a56 on the ground terminal side because there was a defective one and not the transformer is not hissing either.

 

[RockfordFIx]

Found the problem, had a defective ao6 and it was preventing voltage to the zeners for one side of the. Rail voltage is back.

 

[RockfordFIx]

Spoke too soon . As soon as I applied audio the transformers hissed and the powersupply failed. The voltage across the red and black wires feeding the audio 102volts for each side. Voltage at the zeners is 52volts. Does this seem to be too high. Kinda don't under stand why this happened unless the rail voltage is too high. Any thoughts perry

 

[Perry Babin]

52v is about what I remembered the voltage to be. It should be very near the voltage rating of the two series connected zeners.

High rail voltage isn't going to cause the power supply FETs to fail.

When you say that the power supply failed, do you mean that all of the power supply FETs shorted/burned?

Were they clamped to the heatsink?

 

[RockfordFIx]

Yes the outputs for both supplies shorted but it could have just been 2 for all I know. The amp was clamped and it did short out until I connected the rca connectors. No load at this point I was going to look for 60hz signal.

 

[Perry Babin]

Insert a 15 amp fuse into the B+ line feeding the amp.

What is the resistance from the RCA shields to the B+ terminal?

Find the blown FETs by finding the ones with the lowest gate to drain resistance and remove them.

Measure the resistance from the collector of the 4 PNP drivers to ground. Do all read 10 ohms?

 

[RockfordFIx]

Shields to B+ = 120ohms
Ao6 (c=grnd)
All 4 Ao6 = 70 ohm
All 4 A56 = 10 ohm

 

[Perry Babin]

Is this with shorted FETs in the circuit?

 

[RockfordFIx]

With it in, there was only one.
Right side collector to ground
A56 = 10
A06 = 8.28mohm
A06 = 2.652mohm
A56 = 10

Left side
A56 = 10.3
A06 = 8.21mohm
Ao6= 2.616mohm
A56 = 10

 

[RockfordFIx]

Oh I removed and replaced it so all readings are with non shorted 3205's

 

[Perry Babin]

I don't know why the two NPN drivers don't match. I never measured the NPN collector to ground but I'd expect them to match. Maybe it's normal if you don't see any problems in that area.

Did the RCA to B+ resistance increase significantly after replacing the shorted FET?

Decrease the 12v supply voltage as low as possible without the amp's supply shutting down. Do you have a clean square wave for all PS FET gate legs?

 

[RockfordFIx]

I did not check the RCA's to B+ after replacement. I wi get back to you on that result. I will check for a square wave next next.

 

[RockfordFIx]

There was 4 tantalum caps that were shorted. 2 near optocoupler and 2 near the tl494 ic. I didn't have 2uF versions so I replaced them with 0.1uF tantalum caps. Could this affect RC constant or timing of part of the circuit? Not sure I basically installed them to get the unit to power up. I am ordering parts today.