Crate GX-15R Schematic

[chkline]

Transformers are not DC. Set your meter to AC volts to see what is coming out of the transformer.

I will plug it back in, and give it a check. what should I expect to see 14VAC?

[g1]

Probably somewhere around 20VAC between the 2 red wires.

[chkline]

Thanks g1. sure enough, I've got AC voltage across the two red wires. Sure glad I asked before I purchased anything. I'm no EE, and I don't know how much further I want to dig on this, there are just two diodes where it looks like they got hot on the ends, close to where the power comes in, but the rest of the board looks good, nothing looks burnt or bad at all. Any thoughts on what to measure or look at? I did measure across the IC chip mentioned above, and I have voltage across it as well.

[nosaj]

Thanks g1. sure enough, I've got AC voltage across the two red wires. Sure glad I asked before I purchased anything. I'm no EE, and I don't know how much further I want to dig on this, there are just two diodes where it looks like they got hot on the ends, close to where the power comes in, but the rest of the board looks good, nothing looks burnt or bad at all. Any thoughts on what to measure or look at? I did measure across the IC chip mentioned above, and I have voltage across it as well.

How about a picture of the board. A few cheaper amps I've worked on lately(Roland Micro cube being one) They are using these little fuses that look like a red cylinder.

nosaj

[jagora]

I had this same issue except the power light (LED) illuminates and nothing else. I finally got all of the parts through "Mammoth Electronics" but have to be in the mood to do delicate work like removing the actual circuit board from the chassis in order to remove and replace I.C. circuits with soldering technique.

Joe

[chkline]

Here are some pics. I don't see any fuses, which amazes me for an electronic device. The first pic is a close up that shows just a little of the discoloration on the right ends of D18 and D11.

Imgur: The most awesome images on the Internet

Imgur: The most awesome images on the Internet

Imgur: The most awesome images on the Internet

Imgur: The most awesome images on the Internet

[nosaj]

Here are some pics. I don't see any fuses, which amazes me for an electronic device. The first pic is a close up that shows just a little of the discoloration on the right ends of D18 and D11.

Imgur: The most awesome images on the Internet

Imgur: The most awesome images on the Internet

Imgur: The most awesome images on the Internet

Imgur: The most awesome images on the Internet

can't really see the discoloration. Do you have a diode test on your multimeter? If so check those diodes that is your bridge rectifier converts AC to DC.
Also before going too far take a battery and test the speaker You should get some noise when you touch the leads no sound bad speaker. If bad speaker leave it disconnected turn on the amp and measure for any DC at the speaker leads.
I also saw no fuse you may find it hidden in the power plug (IEC).


nosaj

[jagora]

Those are some excellent photo's, I believe what you are looking at are resistors? There should be test points at certain resistors. The only fuse my crate had that was visible was an "In-Line" power fuse. The actual power supply has a stamp on it stating: "Thermal Protected" and after researching, I found out that it's pretty much a disposable power supply. I found my Crate Amp GX-15R at a thrift shop and only cost me $10.00 dollars. It worked great for awhile and then I started trying to connect it to another amp and that's when it broke. Now I am using it a as a learning tool.

Joe

[chkline]

can't really see the discoloration. Do you have a diode test on your multimeter? If so check those diodes that is your bridge rectifier converts AC to DC.
Also before going too far take a battery and test the speaker You should get some noise when you touch the leads no sound bad speaker. If bad speaker leave it disconnected turn on the amp and measure for any DC at the speaker leads.
I also saw no fuse you may find it hidden in the power plug (IEC).


nosaj

I used the diode test on my fluke, and it looks like all. Three passed producing .53 V.

[nosaj]

I used the diode test on my fluke, and it looks like all. Three passed producing .53 V.

Did you reverse the leads to make sure it reads OL in the other direction?
How to test diodes using a digital multimeter
nosaj

[nosaj]

Did you reverse the leads to make sure it reads OL in the other direction?
How to test diodes using a digital multimeter
nosaj

Ok find TP10(at R41 +15v) and TP 11 (at R42 -15v) If we're good there Power supply will be functioning ok.

nosaj

[chkline]

Did you reverse the leads to make sure it reads OL in the other direction?
How to test diodes using a digital multimeter
nosaj

I did, and it did not show OL, it had voltage and would just keep creeping up on all of them. Could these not be diodes? I don't see the normal diode symbol on them?

[nosaj]

I did, and it did not show OL, it had voltage and would just keep creeping up on all of them. Could these not be diodes? I don't see the normal diode symbol on them?

You should be testing with power disconnected. That silver band on one side usually indicates a diode plus the D11 stands for Diode 11.
If your voltages at TP10 and TP11 are -+15v we can move on.

nosaj

[chkline]

You should be testing with power disconnected. That silver band on one side usually indicates a diode plus the D11 stands for Diode 11.
If your voltages at TP10 and TP11 are -+15v we can move on.

nosaj

Power is disconnected, I will check voltage in the morning on Tp10 and TP11. Thanks for all the help!

[nosaj]

I did, and it did not show OL, it had voltage and would just keep creeping up on all of them. Could these not be diodes? I don't see the normal diode symbol on them?

When voltage creeps up like that it usually indicated a cap in the circuit charging. Diodes should usually be tested with one leg out of circuit. But before busting out the Iron Let's go with the 2 test points which will indicated whether the bridge is working ok or not.

nosaj