Crate GX-15R Schematic

[chkline]

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

Went ahead and checked real quick. Double check that I did this correctly, plugged in with power on, I checked capacitor C29 and C31, with the probe and the other side grounded to chassis, and could not find 15v on either side of the capacitor. Also checked the speaker output, and did not have voltage present there either.

[nosaj]

Went ahead and checked real quick. Double check that I did this correctly, plugged in with power on, I checked capacitor C29 and C31, with the probe and the other side grounded to chassis, and could not find 15v on either side of the capacitor. Also checked the speaker output, and did not have voltage present there either.

Just to be clear when checking TP10 and TP11 Amp should be plugged in and on.
nosaj

[chkline]

Just to be clear when checking TP10 and TP11 Amp should be plugged in and on.
nosaj

Correct, amp was plugged in and turned on.

[nosaj]

Correct, amp was plugged in and turned on.

Check for AC at D11 and D14 And D12 and D13 Then check for DC . Amp on.

nosajcrate_gx-15_sch.pdf

[chkline]

Check for AC at D11 and D14 And D12 and D13 Then check for DC . Amp on.

nosaj[ATTACH]44427[/ATTACH]

Amp on, and plugged in, I do not see any DC voltage on either side of D11, D12, D13, or D14, but I do see AC voltage on both sides of all of them.

[Enzo]

This is looking confused. If any of the four diodes were shorted, D11-14, you would be blowing fuses or cooking the transformer. I cannot imagine all four diodes are open. Even one good diode would result in DC.

So connect your black meter probe to ground/chassis, set it for DC volts, and probe TP8, TP9. WHich happen to be the non-grounded end of main filter caps C28, C30. You should see something like 15v at each.

The only way I imagine you having AC at the diodes, but no DC at the TPs is if your CT lead is open. at the transformer connection. It is OK to see AC volts red wire to red wire, but there must also be AC from the green wire to each red wire. For that, leave the meter grounded to chassis, set for AC volts and then probe each red wire.

[chkline]

This is looking confused. If any of the four diodes were shorted, D11-14, you would be blowing fuses or cooking the transformer. I cannot imagine all four diodes are open. Even one good diode would result in DC.

So connect your black meter probe to ground/chassis, set it for DC volts, and probe TP8, TP9. WHich happen to be the non-grounded end of main filter caps C28, C30. You should see something like 15v at each.

The only way I imagine you having AC at the diodes, but no DC at the TPs is if your CT lead is open. at the transformer connection. It is OK to see AC volts red wire to red wire, but there must also be AC from the green wire to each red wire. For that, leave the meter grounded to chassis, set for AC volts and then probe each red wire.

I'm feeling pretty silly now. I don't have AC coming in, I believe the plug may actually be bad. When I check resistance from the plug end to the black and white wires, the white wire shows good, but the black shows open... I'm going to try a new plug wire and see what happens.. I appreciate all the help on here, you guys are very helpful!

[chkline]

Well, I'm feeling like a tool. The cord was part of the issue. I now have power, and it turns on, and the LED lights up, but the sound is very quiet and muted, I can hear the guitar through it, but just barely, and that is with the volume all the way up. You have to get very close to it, to hear it. I tried two different guitars as one is used, and not a known quantity, and both were very quiet. It will pop loud when turning off, so I believe it is getting good power to the speaker, anything obvious you all would suggest I check?

Thanks!

[g1]

The jacks look very corroded or oxidized. They should get some de-oxit or similar cleaner.
What are the 3 jacks labelled as?

[chkline]

The jacks look very corroded or oxidized. They should get some de-oxit or similar cleaner.
What are the 3 jacks labelled as?

I got some contact cleaner and tried doing a little cleaning, but I don't think it is powerful enough of a cleaner. I can't find the deoxit nearby, but hope to pick some up this week. I did get some volume out of the amp after cleaning, if I play the guitar pretty forcefully I will ocasionally get the proper volume from the amp, so I agree, it is most likely poor connections inside, particularly with the patch cord jack...

[jagora]

I have my confidence high to fix my Crate Amp since yesterday, I removed and replaced a volume pot on a Marshall amp and it actually worked. Now I can't wait to finally work on replacing the I.C. Chip and the Op-Amp chip with the huge heat sink.

Joe

[jagora]

How does the heat sink separate from the Circuit chip?