CRATE GX-15R Help

[jagora]

Hello,
I am new to the site and look forward to learning and sharing experiences. I currently need some feedback and help regarding a practice amp I bought at a thrift shop. It's a CRATE GX-15R When I got it home and cleaned it up and plugged it in it worked fine. Then I started trying to make it better by using a 1/4 inch audio patch cord to slave another amp to it. Needless to say, something went wrong because now the power light illuminates and the in-line fuse looks good, but that's it and no sound output at all. The speaker is O.K. and the headphone jack doesn't put out any sound either. I took everything a part and noticed the power transformer had a label on it stating: "Thermal protection Built In" so I don't know if a fuse blew inside of the sealed unit?

The serial number on the power supply is CMEC 94-101-02 and it's made in Taiwan. The actual circuit board is made by SLM electrics p/n 06A233-01 Revision 5
I am thinking what else could have burned or shorted out? a transistor, Op-Amp, or Capacitor? How would I identify it? I am not an expert electronic engineer
If anyone can chime in on my problem I would really appreciate it..

Sincerely,
Joe Agora

[The Dude]

Welcome to the place. It's a good idea to post a schematic or schematic link when you start a new thread. Here ya go.

http://music-electronics-forum.com/a...64-24701c4.pdf

It might help us to know exactly what you patched- from what input to what output. Can you described where the patch cord was connected. Also, your power LED, which you say is lit, is powered post transformer or after the secondary, so I wouldn't worry about the transformer just yet.

[jagora]

Well, That helps some what at least I know not to tear a part the transformer RIGHT?
I plugged the cable from the REVERB input on my Charvel Amp into the EXTERNAL INPUT of the CRATE. IT made a really strange modulating sound and sort of a fluttering in the speaker cone and then I immediately unplugged it. What could I have burned out?

Joe

[jagora]

I replyed to DUDE's post in the wrong area

Hey, Dude
I plugged my CRATE amps additional speaker jack into my Charvel's reverb input jack. What do you think I could have Blown or Burnt ?

[The Dude]

Answer 1 = Charvel Reverb Input to Crate External Input (which I don't see anywhere).
Answer 2 = Crate Additional Speaker Jack to Charvel Reverb Input.

Two different answers. My best guess is Crate "External Speaker" jack out to Charvel Reverb Input. If that is so, my best guess would be that you somehow damaged the TDA2030. It is a guess at this point, unless you want to provide us with some voltage measurements.

[Enzo]

What exactly did you connect to what?

It lights up, so the thermal breaker inside the transformer did not blow.

Start at the start, there are two power rails and secondary rails too. Are those voltages present?

No sound, as in not even a background hum or hiss?

Depending what you hooked to what, you may have destroyed the power amp IC.

[jagora]

What exactly is a TDA 2030? I am working on reassembly at the moment almost ready to apply power but I am somewhat unsure of myself. Electricity scares me a little bit. I know that there are test points on the circuit board but I am not 100% sure of where they are and what the expected voltage should be. This is my first real troubleshooting experience and all I have is a cheap "Gen-Tech" digital multimeter.

[jagora]

Hello Enzo,
I was doing something very foolish and probably burned something out for sure. I wanted the sound coming out of my Charvel amp to sound even better, so I tried coupling the CRATE to the Charvel. It was sounding excellent until I realized that the CRATE was no longer in control. The controls did not work anymore. So I think what I did was hook the audio jack from the reverb on the Charvel directly into the external speaker jack on the CRATE.

Bye the way, the power light did illuminate but no sounds from the speaker at all. I will reassembly and try it again probably tomorrow, that way I can give more accurate information. What is the Power Amp I.C.? Is that the little "Texas Instrument looking computer chip"?

[The Dude]

Here is the datasheet for the TDA2030. It's a TO220 looking device, but with 5 legs. It will almost certainly be attached to a heatsink. If you examine it closely, there may even be a hole blasted out of it or a visible crack, which of course is a dead giveaway.

http://www.st.com/content/ccc/resour...CD00000128.pdf

[jagora]

Hey Dude,
Is that the IC Chip that is in the center of the circuit board with a clip holding it against a fairly large heat sink? I believe it has 3 legs

Joe

[The Dude]

I can't see the amp, so I'm not sure. Can you post a picture? The legs of the TDA2030 are staggered, so maybe that's what's going on here. Look closely. Are there 2 more legs between, but back a bit from the other 3? They won't be all in a row. Also, it should say TDA2030 right on it's face.

[jagora]

I already reinstalled the board on to the chassis and mounted it into the framework, I took a look with an inspection mirror and you are correct, it's 5 legs but I can't see any markings on it because it's flush up against the heat sink. Is there anyway to test it to see if that's the fault?

[The Dude]

Yes. Can you post the voltages on the pins? Be careful not to short them together with your probes. Also disconnect the speaker until we know it's working. It may be putting out or put out DC voltage while you are testing. You don't want to damage the speaker, which begs the question,.... have you checked the speaker? Also measure the speaker output and verify that there is no DC there.

[jagora]

Yes, I will try to do all of these recommended tests however I am not 100% sure I know what I am doing yet. I still have to find exactly where the Test Point #8 and # 9 are located. What is the number on the printed circuit board that indicates Test Point? You have to remember, I have no experience with troubleshooting circuits yet. I understand the concepts and theory but I will have to do a little bit at a time until I gain some self confidence. I don't want to shock myself to death or burn up the entire circuit board just yet

[jagora]

How do you measure speaker output voltage?