Hey All,
I'm new to this forum; however, not to amp fixin' :)
Next on my fix list is a Crate GX20 (it has reverb, does that make it a GX20R?). Anybody have the schematics for it?
Thanks for any help, I've been looking through this forum and it looks like there is a ton of great info here!
Welcome to the forum. Have you tried contacting Crate for a schematic? A lot of manufacturers will send one for free or cheap.
Even without schematic, being a "20" quite probably means it uses a TDA_something chipamp, which usually is what dies, being the part that works harder.
In that case, replacing it plus any visibly burnt resistor may get it back to life.
Post some picture of its guts.
Hey Guys thanks for the suggestions!
Circuit board is pristine, nothing is burnt. All the power supplies are up and running strong.
In my experience the output device (of whatever kind) goes short and blows up the supporting circuitry unless it is protected very well. This one does not appear that way which is why I was going to pull out the scope and start scoping the signal path. I'm not used to working on amps this small so maybe these guys don't "blow" up they just quit working. I'm used to seeing TO3 devices going short :)
The reason I initially asked on here for the schematics is because I've seen reference to them in other posts.
Found These... Hope they help.
Quote from: Bernaner on January 08, 2011, 02:53:14 PM
Hey Guys thanks for the suggestions!
Circuit board is pristine, nothing is burnt. All the power supplies are up and running strong.
In my experience the output device (of whatever kind) goes short and blows up the supporting circuitry unless it is protected very well. This one does not appear that way which is why I was going to pull out the scope and start scoping the signal path. I'm not used to working on amps this small so maybe these guys don't "blow" up they just quit working. I'm used to seeing TO3 devices going short :)
The reason I initially asked on here for the schematics is because I've seen reference to them in other posts.
I think it's a chip amp too. All the supporting circuitry is pretty much on board a chip amp. So no driver transistors as in a discrete amp ala to-3's.
Thanks Mojah!
This is fantastic!
Time to start troubleshooting :tu:
if it's basically the same circuit as the GX20M the later ones have TDA2050 chips...my grandkids have one...also the headphone and external speaker jacks get dirty and make it quit....completely I usually spray some cleaner and then run a plug in and out several times (amp OFF). Starts working again. One of these days I'll change the Jack. FWIW the TDA 2050 does NOT "upgrade" the amp to more output as the voltage supply is still the same as with the TDA2040.
Hey all,
I finally fixed this amp and since it was kind of an odd fix I figured I'd explain what was wrong in case others run into this issue.
I DID replace the main amp IC on a whim; although, I should have trusted my gut instict that it was not in fact the problem. The reason I didn't think it was a problem is that when I turned the amp on, there was absolutly no sound from the speaker. No pop, or thud or speaker movement at all. Anyway, replaced the main amp IC and still no output, so I pulled out my trusty O-Scope and an electric guitar and started scoping the signal path. I had output after the main amp IC and was baffled at that point.
For those of you who do not know this amp, there are 3 choices of output: speaker, headphones, or external speaker. The headphones jack and the external speaker jack are for 1/4" plugs and the connectors for each of them are configured to be normally closed if there isn't a cord plugged into them thus sending the signal to the internal speaker. Well, as it turns out the jack for the external speaker was bent such that it did not make it's normally closed contact and the output signal stopped right there.
I did not have a replacement jack of that type, so I pulled it off the board and completely removed the contacts from the back of the connector (this was the signal not the ground) and then soldered it back onto the board. I then soldered in a permanent jumper across the thru holes that were now missing the pins that I removed. It rendered the jack useless; however, why would you want to hook a seperate speaker cabinet up to an amp like this? It seemed silly to me, plus the owner agreed.
Problem solved... :tu:
Good.
Problems often are not "a bad part" but a conexion or a bad soldering, etc.
You must follow rhe signal path and find where it stops , garbles, distorts, whatever.