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Thread: Crate GX-15R Schematic

  1. #36
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    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.

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  2. #37
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    Quote Originally Posted by chkline View Post
    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.

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    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

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    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

  4. #39
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    Quote Originally Posted by nosaj View Post
    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.

  5. #40
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    Quote Originally Posted by chkline View Post
    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

  6. #41
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    Quote Originally Posted by nosaj View Post
    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

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    Quote Originally Posted by nosaj View Post
    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?

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    Quote Originally Posted by chkline View Post
    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

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    Quote Originally Posted by nosaj View Post
    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!

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    Quote Originally Posted by chkline View Post
    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

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    Quote Originally Posted by nosaj View Post
    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.

  12. #47
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    Quote Originally Posted by chkline View Post
    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

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    Quote Originally Posted by nosaj View Post
    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.

  14. #49
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    Quote Originally Posted by chkline View Post
    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

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    Quote Originally Posted by nosaj View Post
    Check for AC at D11 and D14 And D12 and D13 Then check for DC . Amp on.

    nosajcrate_gx-15_sch.pdf
    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.

  16. #51
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    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.
    Education is what you're left with after you have forgotten what you have learned.

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    Quote Originally Posted by Enzo View Post
    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!

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    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!

  19. #54
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    The jacks look very corroded or oxidized. They should get some de-oxit or similar cleaner.
    What are the 3 jacks labelled as?
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  20. #55
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    Quote Originally Posted by g1 View Post
    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...
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    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
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    How does the heat sink separate from the Circuit chip?

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