Crate GX-65 Transformer popped

[ChancesR]

This amp originally came in with a blown fuse. Very black. Found Bridge Rectifer and filter caps shorted. Replaced. Fuse not blowing now, but the transformer flashes, makes a loud pop and shuts down.

I have replaced op-amps and 2 of the signal amplifiers. No other part faults can be located.

I contacted SLM (spoke to them directly) about obtaining a schematic for this unit, but none are available.

Is the transformer shot? If so, where can I get a replacement?

Warm regards,
C

[Enzo]

The transformer flashes? The transformer itself? That would sound like a bad transformer to me. You would get one from Crate, a part of Loud Technologies.

The schematic is right on the service disc, I don;t know why they wouldn;t have it.

[ChancesR]

Thank you Enzo for the schematic! I faxed SLM, and finally made a direct call - Service stated they didn't even have that schematic. ah well.

Yes, the pop and flash came from the transformer itself. Now I can hope I am able to contact someone at Crate/Loud that knows where to look for this transformer.

I appreciate all you do here on the forum.........a true gift to us all.

Warm Regards,
C

[Enzo]

The part number should be right on the transformer. DOn't ask for a "GX65 transformer," ask for a "94-116-01" or whatevwer it says.

THey ought to have some. Yours is a straight 120v transformer, but the replacement might come as a universal multivoltage one. It will have extra wires and an instruction sheet as to which wires go where for your mains voltage - 120.

[ChancesR]

Many thanks for providing all the info on this. Looking for a possible cheaper-way-out, I tried Google-ing the part number on the transformer - but didn't get a hit. I'll call Crate today. I'll post a 'fix' when completed.

Regards to all,
C

[JustRob]

Try http://www.lselectronics.net
They acquired much of the SLM electronics service parts stock.

[ChancesR]

Greetings all,

Thank you for all of the replies. I also bookmarked the site for parts.

I spoke with the Parts dept. at Crate/SLM/LOUD and was able to get the transformer for this GX-65. Installed - made all the difference in the amp! ha At least I have power.

I have circuit board #06A241-01 Rev 1. The schematics Enzo provided are close, but do have some variations. I'm unable to locate R61, R64 (2W, 0.8Kohm) on the schematic, and not sure if they are correct. They read open. The issue I have now is about 1/2 the voltage(s) of what is supposed to be here. I have replaced all of the IC's, transistors, and all electrolytics on this board. All diodes test good out of circuit.

Whenever I use an Input, R67 overheats. Have replaced this twice now (220 ohm metal film, 1/4W).

I have cleaned the jacks, resoldered ..... tested.

I replaced Q13, Q15 (Output Transistors), and again pulled them and tested out of circuit.

D30 and D31 (Both are Zener 3.3V, 1/2W, 1N746A) test good out-of-circuit, but D30 reads 'short' in-circuit.

It seems I am missing the 5V at the input stage. I have <1V at this point, but I am unable to isolate *where* it's lost.

Any guidance greatly appreciated!

Thanks,
C

[JustRob]

This schematic should be closer, just a few more output transistors, misc. other changes. D30 short in circuit is normal with channel switch out. The two 820 ohm resistors and the 220 ohm are all part of the floating power supply for IC3. Good chance IC3 is popped. Let us know what you find.

[ChancesR]

JustRob - You're the best! Thank you for this. I'll post back soon. Going to pop in another IC3 now.

Regards,
C

[52 Bill]

Exactly what did the amp do before you replaced everything on the board?
What is it doing or not doing now?

Start with the power supply. Since you replaced the transformer are you getting the + and - 40 volts and the + and - 16 volts?

Always try to localize the problem. Randomly replacing parts will often cause more problems than it cures.

[ChancesR]

52Bill: In the beginning, this amp blew several things, transformer, br. rectifier, caps, IC's (2) and 2 transistors. Original fault was "Continues to blow fuses" (per owner). I didn't start shotgunning parts until after the transformer replacement. I had only replaced the known faulty ones. It appears that I have a ground-fault going on here. As I connect *just* the positive lead of the DMM to any point on the circuit board, not only do I get a 'buzz' feeling (which isn't bad....ha), but the voltage readings will briefly display (12V/16V...), then drop to 3.67V. I'm trying to locate this now - where I'm getting the voltage drop.

JustRob: I checked the IC3 against another one in stock. It was good, but just to be *sure*, I replaced it again.

I have not been able to get the 40+/- rail. I have pulled most all of the parts for testing out of circuit on the Power Supply board. Haven't found a problem yet. I've also scanned the circuit board with a magnifying glass, checking for solder faults. Also checked myself to be sure I didn't replace something backwards.......I'm ok there too.

There just isn't that much TO this amp to be causing this much hate and discontent. I've been moving LCD monitors, other amps, and even a battery charger through between the times I 'look' at this amp. Frustrating. And I appreciate ALL of the input - at least it gives me a new perspective to it all.
Thanks so much-
C

[JustRob]

Not getting the +-40 rail? There's hardly anything to it, just the bridge rectifier and caps...What are you getting? Is that with outputs in the circuit?