Crate GFX 120 - Constant hum

[Zip]

Just bought this amp today. The guy I bought it from claims the noise was there when he bought it used. It's rather loud, sounds like 60 cycle hum, and doesn't change on either channel, when volume is raised/lowered, etc. Just constant noise. I was thinking transformer, but I'm a noobie at this stuff and seeing as there are no techs in my area (that I'm aware of) figured I'd try to tackle it myself.

All ideas GLADLY welcomed.

[Jazz P Bass]

GFX 120

I would look at the power supply first.
Check the + - Vdc rails.
If the voltages are correct, switch your DVM to Vac & measure the ripple.
Here is the schematic.

[Zip]

Thanks for that - I had a different schematic. Similar, but just different enough to confuse me

I'll post back what I find out.

[Enzo]

Furst, look at your speaker cones. When you turn the amp on, do they move one way and stay there? In other words is the amp puting DC voltage on your speakers?

The two largest cylindrical parts inside are your main filter caps. Check the solder under them. or at least rock them back and forth a little to see if it affects the hum.

[Zip]

Enzo, you nailed it - it was the filter caps. One read 47, the other 32. Replaced them both & things are NOT humming right along

[jeff venema]

jeff

hey...just got a crate gfx-212....seems that i have the same kinda problem...was just getting static on the input (far left) when plug was moved in the slightest...sometimes it would blast out as the connection jiggled...scary!...anyhow, i opened it up to just clean the plug contacts,and now no sound at all!..lites work,switching works,little red lite is on,
any ideas ???...thanks in advance for any help.....jeff

[Jazz P Bass]

Sounds like broken solder joints where the input jack attaches to the board.
You will have to remove the main board to inspect it.

[gtrplayr1976]

What Jazz said

[jeff venema]

crate gfx-212 reply and thanx for any help...

hey ,happy holidays to all...anyhow I just found out that if i run guitar into regular input,and run ext.amp out to another amp,I get sound,and all controls,except gain1
also halfway into insert I also get sound...but still no regular sound thru the speakers,
I am tempted to just solder wires from ext.speaker jack to my speakers in the amp,but
not sure...any ideas out there?...I DID RESOLDER THE REGULAR INPUT JACK,AND LOOKED CAREFULLY AT MAIN BOARD,BUT ALL LOOKS O.K....HUH???THANX PBASS AND OTHERS...

[gtrplayr1976]

Merry Christmas & Happy New Year ......I still think if you were getting sound when you jiggled the plug, that there's an issue at that input..I'd like to see a schematic...hmmm

[jeff venema]

help!

hey everyone,I have a nasty crate gfx-212...I like some of the sounds it can make.so
I am trying to fix it...too much wrong now,and I am wondering if anyone knowsf a good guitar amp tech near bloomingdale,new jersey??????....thanx, jeff..

[gtrplayr1976]

Same issues ?

[jeff venema]

crate 212

hey,thanx,but now it's starting to fry stuff,replaced a tip142,and plugged her in,instantly smoked two cement resistors...gotta admit,it's getting to me...any ideas?....thanx again...jeff v

[gtrplayr1976]

Which did you replace ,and which resistors blew ?

[jeff venema]

crate problem gfx-212

hey gtrplyr,thanx for getting back to this...i replaced the tip 142 all the way on the left...there is another 142 next to it,then two 147"s on the right,also
first thing I did was check and solder the cliff jack for main input...I was playing guitar with jack halfway in "insert",trying to find what was working or not,this is when tip 142 smoked,like I said before,when I replaced(with a little bigger tip 142,no metal tab,just a screw hole on top,which i did,then plugged her in,and two cement guys fryed..I will get the numbers now,and get back to this asap..thanx...