B&O 8002 / R43 failed / OM1 will not operate / Replace semi conductors ?

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cometphoton Posted: Sat, Apr 18 2020 12:56 AM

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I have a 8002 that had a blown power supply fuse. I opened and the OM1 (transport motor) belt was loose. So I replaced the belt. Next I found R43 had experienced high current and was toasted. Replaced R43 and Replaced the all electrolytic caps on the pc board.

Powered up. R43 got hot again. Hmm..Fuse didn't open this time so it must have been from something else before. But R43 is scorched.

Now OM1 will not operate with the belt on. But when you take the belt off you can drive OM1 in both direction but the motor torque is too weak to operate the belt. " R43 maybe causing this. 

I cleaned the linear drives mechanical screw drive assembly so its a bit smoother.

Looked at the schematic. No clue what is causing the current problem across R43 so I will replace the NPN and PNP transistors and diodes associated with the motor control circuit next.

My question what parts today replace the parts from yesteryear. 

I see two NPN "PU 01" (TR1 TR3) and two PNP "PU 51" (TR2 & TR4) ?

Do I use NTE parts ? HELP

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Dillen replied on Sat, Apr 18 2020 8:13 AM

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I doubt this to be an electronic problem. More likely a motor problem.
Check the motor current.
And check that the motor is able to run on just 2-3V, easy and slow..
It's not uncommon to see this motor in need of cleaning and fresh lubrication.

Martin

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cometphoton replied on Sat, Apr 18 2020 3:15 PM

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I examined the motor, seems aok, added new lube too. I will try to operate as you recommend. Let see what happens

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cometphoton replied on Sat, Apr 18 2020 3:32 PM

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Bingo the motor is running very smooth at 3 vdc. tested R43 = 22 ohms. Good to go for a test.

1. Logic

Power up. the LED display has a decimal point only.

Press play turntable spins  (33.33 in display) and the transport indexes 1/2 way to the LP. not making it all the way to the LP

Press << transport moves toward center of Platter. moves fast ( working fine now )

Press >>Transport to home fast or slow operate as it should. Fast or slow.

Press Play transport index inward stops 1/2 way between LP and home ( tone arm is not dropping ) 

Press stop the led arrow display toward home but nothing else 

Press Transport to home and hold transport moves to home hits limit stops turntable turns off.

Need to trouble shoot play logic and center indexing ?