68kMLA Classic Interface

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low voltage Classic
Posted by: bibilit on 2017-09-19 23:41:48
Not lucky with Classic ABs.

I have a Classic at home, Logic board has been recaped and working great, but the AB is not delivering the proper voltages.

New caps in the usual area and new Optoisolator as well.

The 12 v is around 11.4 at best and the 5 v is around 4.5 v.

the screen is wobbling also, even when voltages are fine (managed to crank voltage for a test)

Any idea welcomed.
Posted by: bibilit on 2017-10-08 07:57:37
Another one solved.

Here, The Analog board was the late model, 220 volts type.

Voltage at pin 6 of the TDA4605 was a bit low also, and PP1 was not able to crank the voltage high enough.

replaced both diodes DP4 and DP3 (1N4148), capacitors CP4 and CP5 (47 uf/25 volt and 1 uf/50 volt) and touched weldings around :

IMG_1351.JPG

IMG_1352.JPG

IMG_1353.JPG

Both diodes were leaky, now PP1 can be adjusted.

So all in all those two diodes have a high failure rate.
Posted by: sigtau on 2017-10-08 11:44:41
Wait a second, you're telling me that diodes can leak too?
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