Beogram 8002 – Power on/off signal

[Doc99]

I’m working on my Beogram 8002. Just finished replacing the electrolytic caps. The platter does not turn. If I press a speed button, the speed selected does show up on the LED display. The +15 and -15 supplies do not turn on. Traced it to the power on/off signal that comes from the uP.  Checked and there is continuity (3.3K) from the power on/off transistor TR21 back to pin 38 of the uP.

Does anyone know if there are other signals that must be present for the uP to bring the power on/off signal low?

Thanks,

Doc

[Mark-sf]

Are you getting a voltage change when you press start on pin 38? Do you have 5v on the collector of TR21? I would also double check your replaced cap polarities against the schematic (not the board).

• This reply was modified 1 month ago by Mark-sf.

[Doc99]

TR21 is on as I’m seeing 0.6V on the base and the collector is close to gnd. The collector at gnd is forcing off the +-15V. Good idea to try and pull the base of TR21 low and see if the +-15 turns on. That probably waits until next weekend. In the meantime I’m bring the board into work. I used a hand magnifier when reworking and feel pretty good about not causing any shorts or opens, but will check with a microscope. I marked the negatives on the board as each cap was replaced. However, will check just in case.

Thanks,

Doc

[Doc99]

Maybe I’m missing your point about asking about the start button. I am not ready to test the tone arm movement. I am using the 33 or 45 button to start the platter. Is the +-15 not needed for platter rotation?

[Mark-sf]

The motor circuit requires the 15v supply to operate. The TURN button is used to rotate the record for cleaning, not the 33 speed button as was the case on the older models. The 45 button never turned the platter.

 

[Doc99]

Thank you. You are correct. The TURN button turned on the +-15V supplies. The motor did turn on upon reassembly. Not sure if the speed is correct. I need to find my strobe disc.

I do see an intermittency in the motor circuit. Found that moving the connector attached to P4 is part of it. Moved it and the platter started turning. One time when moving P4 there was a white on/off illumination on the component side of the board when moving it. Couldn’t see which component it was. It was about an inch away from the P4. When that happened a 0 appeared on the display and none of the buttons worked. Power cycled and everything came back ok including the platter turning.

Don’t see any cold solder joints or broken traces on P4 or the parts in that area. Nothing looks or smells smoked. Will resolder P4 for good measure and check under the microscope again.

[Doc99]

Noticed some crud that is coming out from where one of the leads exits from D40. D40 is a glass diode and could possibly glow  under a failure. Will replace D40 and check again next weekend.

[Doc99]

Motor circuit is now working correctly. Found the PCB was cracked causing opens on the traces going to P4 pins 1 and 2. The crack started at the edge where the board is slide under the retaining clips in the cover.  Likely this was self induced the first time the board was either removed or reinserted. The illumination seen was from flexing of the PCB when pushing on P4 and the traces would connect and disconnect from the pressure. Used super glue on the crack and added a stiffener across the crack with epoxy. Added a couple of wires and the motor works.

As noted, this was self induced. I still need to complain a bit. When I purchased this new in the 80’s, it was a high end device and priced as such. Wish they would have used FR-4 instead  of phenolic board material.

 

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