CRATE GX-15R Help

[Jazz P Bass]

Set your VOM to read Volts ac.
Hook it up to the speaker.
Turn the amp & guitar up.
Wail away.

V x V / spkr ohms= watts output

[jagora]

That sounds a bit dangerous and unsafe. I'll have to double check this.

Thanks
Joe

[J M Fahey]

With due respect, leave that amp aside for a while, maybe in the future you can get back to it and fully repair it.

For a smoother learning curve I suggest you get into one of the Pedal building sites, and build a couple.
Start with a single transistor booster, similar to EH LPB1 .
Relatively simple, real inexpensive and runs on a 9V battery, is an "essential building block" as in you can truly say that most preamps and power amps "are basically the same, just with more parts" , it gets signal in, amplifies it, is powered by a supply, is biased , the works.
Then follow with a simple amplifier, like Ruby or similar LM386 powered ones, then with something using a TDA2003 ... and you are smack in the level of what your amp uses
NEXT project will be repairing your Crate amp, but now with some experience and knowing what you are doing .... how´s that ?
But go step by step.

IF you don´t want that, just repair *this* amp and forget anything else, simply replace the TDA2030 chip amp with a new one (don´t forget the mica insulator and thermal grease or get a TO220 SilPad), it *should* be enough.

[DrGonz78]

That amp has a very tight fit for the circuit board into the tiny little chassis. Years ago, I remember it was a bit of a pain just getting the circuit board out of the chassis thanks to that spring reverb that is totally in the way. That also explains why you could only see 3 legs on the TDA2030 chip, very tight fit. Even on an amp that has more room in the chassis it can be really hard to touch a probe to the back 2 legs of a TDA2030, 2040, 2050 IC, very easy to slip with your probing. That is why being able to read the schematic while tracing connection points is so important. Instead of probing those tough to reach back 2 legs of the chip you can find other easier to reach direct connection points for safer probing.

With that said you can disconnect the speaker and measure DC voltage across the speaker leads. If you have any significant DC voltage on the speaker out connections then it most likely a blown TDA2030.

[jagora]

Hey Dr. Gonz,
I appreciate the help and heed the warning of touching the wrong terminals due to cramped space. You should have experienced removing the circuit board from a "Fender Frontman" now that's too tight. At any rate, you say to check voltage across terminal leads of the speaker. Do you mean place the Red probe on the Positive terminal and the Black probe onto the Negative terminal? Then you mention "Speaker Out" is that the 1/4" Jack on front of the amp right beside the Headphone Jack?

Joe

[g1]

He said disconnect the wires that go to the speaker and measure the DC voltage at those wires. One probe to each wire.

[jagora]

O.K. Will try that. Also, do you know of an electronics company that sells the 1/4 inch input jack (pc mount) with the chrome nut and has 4 pins

Joe

[jagora]

Hey Mr. Fahey,
I wanted to ask you if you could tell me the exact transistor number that serves as "Test Point" number 8 and Number 9? I understand they are located somewhere right past the four diodes leaving the power input: D-11,12,13,14 I understand that Test point 8 should read 15V+ DC and Test point 9 should read 15V- DC providing you have the multimeter set on 200 or is it 20 Volt Direct Current?

Thank You
Joe

[DrGonz78]

Find R41 and R42 on the board... One side of R41 is TP8 and the other side is TP10. The same is true for R42 for checking TP9 & TP11.

[Randall]

See if you can find it here;

Switchcraft : 1/4" Jacks and Plugs

Then buy it here:

https://www.tubesandmore.com/products/jacks_plugs

[Enzo]

Crate used Cliff style jacks. The chrome nut like old Marshalls would not likely be stock on this practice amp, though it should fit. As far as I know they all had the black plastic nut.

Randall's tubesandmore connection still should have them. Look under Marshall jacks for the chrome nut kind. If it has 6 legs, snip the middle two off. Look under Cliff jacks for several black plastic nut types.

[jagora]

Wow Dr.Gonz,
You are Awesome, this help me so much...Thank you Sir!

Joe

[jagora]

Randall,
Thanks for the info. I will wait to see what happens with my repair project before deciding to buy upgrade parts

Joe

[jagora]

Enzo,
You are a sharp thinker, I like your creative thinking.

Joe

[jagora]

Hello Again Dr.Gonz,

I checked the resistor test points and they check good (approx 15V+ and a 15V-) went to check the speaker leads and had the meter set on 2000K on the Ohms range and got a reading fluctuatining between 13 and 15. Not sure if that's an indication to move on to the next component check being the TDA 2030?

Joe