Crate GFX 120 - Constant hum

[jeff venema]

hey folks...was gone the week,but now back..will get on this tommorow,tuesday,and follow up...thanx,gtrplr

[Roshihyde]

I think I have the same problem Zip had.

Except I have a Crate GFX-212 and when I first plug it in it works fine, but after I play for a few seconds with some volume to it it the amp starts to cut out and I get the hum. I have a basic knowledge of electronics but the amps a little advanced for me. Can anyone tell/show me what needs to be replaced and where I can get it?

[52 Bill]

Except I have a Crate GFX-212 and when I first plug it in it works fine, but after I play for a few seconds with some volume to it it the amp starts to cut out and I get the hum. I have a basic knowledge of electronics but the amps a little advanced for me. Can anyone tell/show me what needs to be replaced and where I can get it?

Welcome to the place. Try giving the amp a whack with your fist. Does the hum start or stop with the mechanical stimulation? If it does, open up the amp and see if the large filter caps are loose or unsoldered. This is a fairly common problem with a lot of amps.

[Roshihyde]

I hate to admit I've already tried the punching trick and yeah it responds about half the time. I've taken it apart and one of the filter caps feels loose. Should I reheat the existing solder, or should I add more?

[Enzo]

RE-solder it, yes, add more.

[Roshihyde]

Ok I soldered it and it doesnt wiggle anymore but I put everything back together except the effects board and now Im getting no power

[DrGonz78]

Ok I soldered it and it doesnt wiggle anymore but I put everything back together except the effects board and now Im getting no power

Not sure but is the effects board still removed from circuit? If it is then possibly you have an issue there if it needs to be connected to make a circuit connection to be able to power it on. Put it all together exactly the way it was to be sure. Also, check fuses and wiring etc...

[Roshihyde]

Ive played it with the effects disconnected. Ive switched around the only two wires i couldnt exactly remember where they went and got nothing either way

[Roshihyde]

I may need a new fuse. When I test the power Im not getting anything past it.

[Enzo]

ALl those individual push-on wires. Make SURE they are in the right places. COnsult the schematic.

[Roshihyde]

I cant seem to find a schematic for my model. Anyways the fuse actually looks dark on one end. Im going to replace that tomorrow and I'll let everyone know how that works. Ive checked with a voltage tester and I'm getting nothing past the fuse.

[DrGonz78]

Use your meter on ohms setting to see if the reading is near zero resistance end to end on the fuse. If the meter can't register a resistance then it is open, and check your meter if it has a continuity setting with a beep sound. If it shows like 1ohm or less or a beep sounds(continuity setting) then it has continuity and it is probably good. Just changing fuses will often not fix the problem, but if it does then yay!! You know you really should open up a new thread as I am getting confused which amp we are talking about here... GFX 120 or GFX212

Check this link here for the schematic...
http://music-electronics-forum.com/t20270/

The site has been running slow lately so the downloads might take a bit.

Edit: Crap the link is the one that is missing on that page. Will someone repost that schematic if they have it? Plus there are times that a schematic is shared amongst other similar models. GFX model 120 might have a very similar layout.

[52 Bill]

I'm more concerned about why the fuse has blown.

Do as Enzo suggested, make sure that you have wired it back up correctly before you blow another fuse and possibly additional parts.

[Enzo]

GFX120 and GFX212 use the same schematic.

[Roshihyde]

ok I found a schematic, but its a little confusing. There is no J16. Heres a link to the schematic I'm using CRATE GX 120, GX 212 SCH Service Manual free download, schematics, eeprom, repair info for electronics


J19 and J20 are on the same route and both behind the capacitors, so the negative wire should be able to go to one of those, right? Sorry Like I said I have a basic knowledge of electricity and such but this is the first time Ive really needed a schematic to repair something electronic