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robcontact

USA
2 Posts

Posted - 08/20/2016 :  14:36:25  Show Profile  Reply with Quote
Hi all,

I have a GMC-200 that my mother gave to me to "fix". The only obvious problems that I can see are a couple of SMC resistors (probably resistors) that appear to have... disintegrated. I have no idea what the story is behind it no longer working, but I thought I'd ask here if there is a way to find out what the values are of the pieces that seem to be broken.

I've attached a picture with a red square over the components that are obviously broken, and an arrow to a black component that may or may not have burnt.

Any hints?

Image Insert:

369834 bytes
Reply #1

Distelzombie

Germany
176 Posts

Posted - 08/21/2016 :  00:34:20  Show Profile  Reply with Quote
The red arrowed component is definitely dead. It may be a diode. Put an LED in...

It looks like you could pull out the right resistor from underneath the DC in. Maybe you can read it's number.
Youre missing only one number. Between the 2 and 0. Try to make it out by a close examination of the remaining parts and then put it in here:
h**p://www.hobby-hour.com/electronics/smdcalc.php

GMC-300E+ V4.20 with sbt-11 alpha tube

My statements are to be taken as stuff-a-hobbyist-says.

Edited by - Distelzombie on 08/21/2016 00:45:15
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Reply #2

flukeguy

USA
6 Posts

Posted - 08/21/2016 :  04:44:50  Show Profile  Reply with Quote
Hi Robcontact:

Found 2 pictures from this forum of clear pics of the circuit board:


http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=3407&SearchTerms=diodes

http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=3426&SearchTerms=200

Good Luck!

--TJ

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Reply #3

Distelzombie

Germany
176 Posts

Posted - 08/23/2016 :  03:48:56  Show Profile  Reply with Quote
Cool. Interesting threads that you found!
Anyway, there could be something else broken, but the two 2R0 are just used as fuses. They are 2 Ohm resistors. You COULD just short the contacts. I don't think it's important if the value is under 2 Ohm. But it's obviously not advisable to do so.
It looks like your mom tried to use a 12V DC adapter or something like this. You should check this before giving it back or she'll blow it again. (Your mom blows, dude!) xD

I don't know what the black component is. It could be a diode...
... Yep, it is: h**p://www.kingtronics.com/diodes-rectifiers/m7-diode.html

GMC-300E+ V4.20 with sbt-11 alpha tube

My statements are to be taken as stuff-a-hobbyist-says.

Edited by - Distelzombie on 08/23/2016 03:58:03
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Reply #4

ZLM

1055 Posts

Posted - 08/24/2016 :  12:21:34  Show Profile  Reply with Quote
It seems wrong polarity DC adapter used. Replace those three components. The D4 should be regular 1N4001 rectifier diode.

If no other component broken, then it should work.
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Reply #5

robcontact

USA
2 Posts

Posted - 08/24/2016 :  13:50:40  Show Profile  Reply with Quote
Thank you all for your answers! I'll give it a shot. I couldn't have even attempted this without your help!

Thanks again,
Rob
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