Electronic equipment repair and service manual search discussion :: Topic review - Need some advice repairing a CRT Black & White TTL Monit

gehrig · Posted: Tue Apr 29, 2008 12:22 am Post subject:

It was Q13.. I replaced and everything is up and running.

Thanks for the replies!

vtech · Posted: Sat Apr 19, 2008 5:20 am Post subject:

Sure points to a bad Q13. ...still, no reason why you can't test it? (yes there are odd instances where the testing may not show it but definitely not in this case)
A leaky Q13 can easily be spoted with an ohmeter.

http://www.hobbyprojects.com/test_and_measurement/testing_transistors.html
http://www.kilowattclassroom.com/Archive/AN0007.pdf

Also, more than likely, you don't have to get an exact replacement number for Q13.

Guest · Posted: Sat Apr 19, 2008 12:25 am Post subject:

I pulled the collector on Q13 and powered on. The voltage reading jumped from 30 to about 70. So, thinking Q13 must be bad then? I have one on order..so thinking maybe I shouldn't try anything until I replace. What do you think?

gehrig · Posted: Fri Apr 18, 2008 6:43 pm Post subject:

I see. Thanks for the info. I will give it a shot this weekend.

Guest · Posted: Fri Apr 18, 2008 5:30 pm Post subject:

Sorry I meant with Q13 removed place the probes on the print of the pcb where the legs would go if it was still installed.
Regarding your update voltages it seems to be a drop of 40v going somewhere. If Q13 was removed and you remeasured these points it would prove Q13 was doing this.

gehrig · Posted: Thu Apr 17, 2008 11:48 pm Post subject:

Hey.. just an udpate.. here are my voltage readings off of the transformer.

gehrig · Posted: Thu Apr 17, 2008 10:22 pm Post subject:

I meant.. just remove the emitter leg and check B and C..

gehrig · Posted: Thu Apr 17, 2008 10:20 pm Post subject:

I'll check look into the resistor voltage readings tonight.

I am a newb at this....I dont understand how I would check the voltages of the E and B of Q13 if it is removed. Do you mean just remove the collector leg?

Guest · Posted: Thu Apr 17, 2008 8:26 pm Post subject:

What is the voltage at both sides of R56 and voltage drop accross R56 and R58? Remove Q13 and state voltages at base and collector.

Guest · Posted: Thu Apr 17, 2008 7:56 pm Post subject:

Thanks for the responses.

I removed Q13 and checked with my DMM that has ohm readings before. It passed the tests. However, I read that this doesn't mean it couldn't be bad. Since the work load using an ohm meter (DMM) is so much less. I haven't even checked my transformer, due to the fact I don't know how. But, I am reading up on that now.

I recently purchased a scope, but still learning how to use it. The wave forms I was getting on the Q13 looked much like an AC wave form. All other transistors looked nothing like they should according to the repair manual.