Discussion in 'Yamaha' started by super j, Feb 10, 2018.
It was low millivolts. I wrote the numbers down somewhere.
No relay click and mV on those resistors indicates a failure in the protection circuit.
Problem could be anything like a failed/out of spec cap, transistor, diode, relay or even
a dry solder joint. Will need to get some test points for voltage measurements.
Suggest check the relay for continuity, measure the resistance across D719 in both directions, amp unplugged/powered off.
Also measure dc voltages to ground for TR702 e/c/b
I started looking at the power supply board and the capacitor board. The two 33 ohm resistors from the service bulletin had desoldered themselves. I resoldered them to see if that would resolve the problem, but it didn’t help. I still plan on ordering parts for the service bulletins and possibly recapping the board while it’s out. Is there a parts list anywhere for recapping the board?
I’ll check for the measurements across the diode and the transistor this afternoon.
For D719 I have 159 ohms on the cathode side and 0.5 ohms on the anode. For TR702 I have 14.3 vdc on both outer legs. I believe that's the emitter and base. And -5mv on the collector.
TR702 2SB544, b,c,e makes 14.3V on b and e. I always like to see that 0.65Vbe.
The collector drives the relay. -0.5mV is not going to do it. Please diode check
TR702, in circuit ok, looking for a b-e short. If you have a suitable replacement
you could try it.
What do you mean by diode check? I have a diode setting on my meter but I've never used it. Using that across the transistor, base to emitter and vice versa, i get 223 millivolts. I'm not sure if I'm dong it right, though.
These are the readings I got between all the legs.
For the above readings I used a tutorial I found on google. My meter has a setting with and ohm, a diode, and the audible alert sign. Set to diode I got the voltages above. Using the alert sign I got OL for every reading except e-c. For e-c and c-e I got 280 ohms.
The were done in circuit as per mbz above. These readings don't look good according to the testing transistors page.
Erroneous readings -- need to test them out of circuit. To be accurate.
Thanks. I'll try to pull it out tomorrow or the next day. You recommended this replacement in an older thread I found. Should I buy this one if I need a replacement?
Mouser #: 512-KSA1013YTA 1ea .19
Yeah, I was kinda trying to save you some work with the incircuit tests looking for a short so alternative paths don't come into play.
Looks like the transistor hasn't failed outright, might be in the process of dying. Don't like any of the readings, don't see the alt paths
to explain them. Easy enough to pull the transistor as per avionic...
I removed the transistor, but I don't believe my meter is capable of the continuity test that is on the transistor test page. It won't read high enough. I ordered a new transistor when I ordered the resistors for the sb so I soldered the new one in, but there was no change. Still no relay click.
I checked the continuity test on some resisitors and it would read up to around 450 ohms. Anything above that was OL. I can always take them to work and use my fluke if I need to in the future.
Your DMM is looking a bit unreliable. The in circuit test results/post #30 are hard to work out. Might be time for a new tester, something like the
Mega328 transistor tester on ebay, cheap and nasty but does the job. Some have a plastic case, important to check the features, some have old SW.
I checked the manual for my meter. It says the continuity test goes to 50 ohms, but I believe that’s a misprint. I tested resistors up to 500 ohms. Everything over 500 was OL.
While checking some voltages, I accidentally shorted the base to the collector on tr702, with my meter. The relay clicked on while they were connected. I'm not sure if that tells me anything.
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