Crate GFX 120 - Constant hum

[g1]

You need the GFX schematic, the GX will not be the same.

[Jazz P Bass]

Crate GFX212 Schematic

Here is the GFX212 schematic.

[Roshihyde]

Oh wow this one looks right. Thank you so much now as soon as I get a fuse everything should be in order.

[Jazz P Bass]

If you are all that sure about the wire placement, try this test.

With a new fuse installed, place your ohmeter, set to read resistance, on the power cord tangs. (not the ground)

With the power switch ON you should be reading the resistance of the power transformer primary.

15- 30 ohms, or something close.

Neither of them should connect to chassis ground.

[Roshihyde]

Ok the ones ive marked in white are the ones im confused about the ones marked in blue the red X is what I re-soldered and the yellow is to follow that one wire.

Do I have it right?

[Jazz P Bass]

Do I have it right?

The proof is in testing.

Please do as I suggested in the post above.

[Roshihyde]

Ok I got a new fuse and put everything back together, I have power and sound but I'm still getting a hum and a good bit of pop and crackle. I'm posting a video of the test after I turned it on. Ignore the fact that my overdrive doesnt work right away I had it turned all the way down. You can only really hear the popping and crackling when I play clean in the video, but it is still there with the distortion but you can only really hear the volume fading out when I'm using distortion. and if you'll notice the hum is there with the volume turned all the way down.

[Roshihyde]

Guess you guys took off for the holidays. Merry whatever you celebrate everyone

[g1]

Plug your guitar into the insert jack and see if the noise/hum is still there. This will help determine if the problem is in the preamp section or power amp.

[Roshihyde]

I still get the pop and crackle on either input or insert. It also seems I'm only getting about a quarter of the volume I'm supposed to.

[g1]

Have you verified that the speaker is good?
Do you have +/- 40V supplies in the power amp section?

[Roshihyde]

Do you have +/- 40V supplies in the power amp section?

Sorry but I cant say I understand what you mean. I'm quite novice at this.

And yes the speakers are good. Before I re-soldered the filter caps they worked fine after i punched the top of the amp lol.

[DrGonz78]

okay looking at the power transformer you will see J17 (white) & J19 (black) feed in your 120VAC voltage. That power transformer is stepping down the voltage to roughly around 40volts and then that is fed back to the board through the two red wires, J26 & J28. At that point the AC voltage is rectified to DC voltage, research this concept if you are unsure. It is a bridge rectifier I think but it is labeled D24 on the schematic. Look for a black square looking creature... You will see four markings on the top (~ + - ~) ~ symbol = incoming AC voltage. The -/+ symols are the DC negative/positive voltages after it is rectified. Then those main filter caps will be next to remove(filter) unwanted AC ripple left over in the DC voltage.

So we want to measure each side of the filter caps for one cap will have -40vDC and the other will have 40vDC. That is what G-One is asking when he said "Do you have +/- 40V supplies in the power amp section?"

Keep reading the schematic and tracing out the board to see how those parts all connect. Do not measure something if you are at all unsure and take the amp to a tech if you don't feel comfortable. Ask questions if you are unsure and we can help you along.

[Roshihyde]

Guess I should start asking relatives if they have all the testers and tool I need. What are the testers I need called?

[Jazz P Bass]

My thoughts on this post are that #1, you have a 'working amp'.
I am not too sure why you have not taken it to a tech.

Not to belittle you, but I do not feel that you are up to the task of properly troubleshooting & repairing this equipment.

As is stands, you may incur a small charge to get it repaired.

One slip of a test lead and you can x's 4 that figure.