Guitar Amp Issues.

[DaPiMan]

Good day.
So I have myself here a Crate GT65 65watt combo amp, 12inch speaker, solid-state, which -as I'm posting here- obviously has a problem:

I turn it on and start playing, and it works fine for a couple of minutes or so, after which time it makes a loud pop (similar to what a lot of amps do when first turned on) and goes silent. After a minute or so, it starts working again. For a minute or so, and the cycle repeats.

Now, regrettably, I'm not as electronically talented/educated as I would like to be, so my best guess is that some component is overheating and disconnecting, though not anything I have as yet been able to notice. Nothing appears to be loose or damaged, so I'm coming to you in hopes of some sort of direction or guidance.
I may not know all the terms, but there's nothing I can't figure out or learn.

It's not a life or death kind of thing, I have a better amp, but this one is lighter, and easier to haul around (and when it's not cutting out, it sounds great). I'm just looking to have my stuff work. ^_^

 

[Jon Wilder]

Solid state amplifiers are not something a novice with very little understanding of electronics should be playing with. They can be quite complex and without a schematic for the amplifier it is near impossible to analyze the failure mode.

That being said, it could very well be something getting hot, and the trick is to find what's getting hot and what components could possibly be shorted to cause said components to get hot.

I'll get ahold of SLM Electronics tomorrow and see if they can email me a schematic for that model. From there we can proceed further.

 

[4pyros]

Here it is;
https://elektrotanya.com/crate_gt_65_120a_sch.pdf/download.html
Its only sheet 1 of 2 and seems to be missing the power circits.

 

[Nigel Goodwin]

Here it is;
https://elektrotanya.com/crate_gt_65_120a_sch.pdf/download.html
Its only sheet 1 of 2 and seems to be missing the power circits.

Unfortunately the fault is almost certainly in the power circuits.

 

[bountyhunter]

Sounds like maybe the output stage bias is wandering far enough as it heats up to pop a circuit breaker.

 

[4pyros]

Unfortunately the fault is almost certainly in the power circuits.

Agreded, its ether in the power supply or the output amp.

 

[ononomos]

Possible your final output amplifier has a flawed thermal attachment to its heat sink. Easiest way to check is to see if it still acts up even if you aren't playing (since that will cause much less heat). If it still pops in and out, I'd start with the power supply.

First thing to check is low-voltage supplies from the power supply to the amplifier section. They should be easy to reach with a voltmeter. Be careful you don't go near the high-voltage/mains/220V/110V/what-have-you leads, and don't short your meter probe between two circuits or you could cause a lot of damage -- instantly.

If you determine that a low-voltage supply has a bad component, you can compare before & after in different spots to see what's failed. Have a friend play so you can take notes on voltages.

For my money, you may find a bad diode or filter capacitor. These are easy to find and replace.

Also possible it's something as dumb as a bad plug or jack from your guitar cable. Did you try another guitar and cable, and cleaning all the conductors? Jiggle the AC power cord to see if it's failed inside the insulation?

 

[33by47]

R56 a 2.2 meg resistor (two 1 meg resistors in series from radio shack) and
C38 10 Ufd @ 35 v
(both near Q16)
Could cause "goes silent" but not sure about "makes a loud pop".
I would just replace those two parts

 

[unclejed613]

funny, i was able to download the pdf off of that rather UN-user-friendly page on the link that says "Get Manual"....

3 places you should measure voltages are: the +/-16V rails, and the side of R70 that goes to the two transistors (Q14,Q20). Crate seems to favor the zener method of getting the +/-16V rails for the op amps, and this is very unreliable (same thing goes for similar Fender amps, the zeners are always dying). if you lose one of the 16V rails, you will get a pop and no audio. if you lose the supply for the diff amp (Q14,Q20), you will get a pop (probably with a few volts offset across the speaker) and no audio.

 

[Tann-44]

Good day.
So I have myself here a Crate GT65 65watt combo amp, 12inch speaker, solid-state, which -as I'm posting here- obviously has a problem:

I turn it on and start playing, and it works fine for a couple of minutes or so, after which time it makes a loud pop (similar to what a lot of amps do when first turned on) and goes silent. After a minute or so, it starts working again. For a minute or so, and the cycle repeats.

Now, regrettably, I'm not as electronically talented/educated as I would like to be, so my best guess is that some component is overheating and disconnecting, though not anything I have as yet been able to notice. Nothing appears to be loose or damaged, so I'm coming to you in hopes of some sort of direction or guidance.
I may not know all the terms, but there's nothing I can't figure out or learn.

It's not a life or death kind of thing, I have a better amp, but this one is lighter, and easier to haul around (and when it's not cutting out, it sounds great). I'm just looking to have my stuff work. ^_^

Hello Dapiman...if your unsure where to start to try repairing your amp do some reading about electronics as it can be painful getting a shock... before jumping in a removing parts..place your meter black lead on the chassis (earth) and set it to 200dc range and check if the power supply caps have any volts...to drain them flat..use a 100 ohm 5watt resistor across each cap this will drain them.. now remove them and re power up with no speaker connected and check there voltage,,.standard ht would be 40vdc +/- volts dc followed by 15+/- volts for the front stages...