Beogram 4000 and also BG8002

[hcraig244]

And again with the desk lamp switched off, again not very close but I’m encouraged by the change in resistance from lamp on to lamp off.

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[hcraig244]

Connected the control panel back up with the cover still off the lampbox to view the operation of the lamp itself…I know these old incandescent lamps go off in time, and when I powered up sure enough the glow was a little subdued

 

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[hcraig244]

However I was astonished to see the platter spinning and the pick up marching happily across the deck and back!

I have a very bright flourescent lamp above the workbench along with the desk top magnifier lamp, when I turned off the magnifier lamp the unit still functioned as above, when turning off the flourescent tube the pickup arm moved to the drop area and held up there….I will try later with the lampbox cover in place to see if it can be adjusted but having seen the above I’m thinking a new lamp with more lumens will be required, and in doing so i feel the photo resistors should be replaced at the same time….any advice Mark/Dillen?

 

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[hcraig244]

Lamp box cover back on, adjustment screws would all the way out and could not get the voltages at P5 pins 4 and 6 below 1,5v and 960mv respectively…and the pick up moved its usual 2cm and actually did wander very slowly further in…

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[hcraig244]

Lampbox cover back off…..the voltages at P5 pins 4 and 6  840mv  and 630mv respectively….and the pickup moved nicely across the platter and returned to rest….looking good.

New lamp and photo cells is my conclusion…unless anyone has anything to add? maybe replace the lamp alone would be enough?

Craig

[hcraig244]

New components have arrived….decided to replace the lamp and both LDR’s

 

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[hcraig244]

Separated the control panel PCB from the pushbuttons and de-soldered the two LDR’s and the lamp, soldered in the new components…the new LDR’s are smaller than the originals however I’m confident they will function correctly.

 

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[hcraig244]

Replaced the lamp box cover and connected the control box up…powered up and with a disc on the platted hit start, everything operated correctly, the platter spun, tone arm moved the drop position, and it dropped onto the disc, with no cartridge so I hit pause and the tonearm lifted and waited for the next instruction..,,I adjusted the LDR adjusting screws and managed to get them both to around 560mv (should be around 600 to 700) so we’ll see…..it may be due to slightly different LDR’s fitted? however when I operated >> and << everything worked fine….so I’m calling this a win!

Just need to replace the carriage drive belt on this, replace the double sided tape on the wayward panels, set the carriage travel sensitivity once we have a cartridge fitted and this is done (famous last words I know)

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[hcraig244]

Belt replaced with new one and re-assembly commenced, had to think about this as its a while since I took it apart ;¬)

 

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[Mark-sf]

Actually what you are observing is the 8002 going into protection mode and locking out all functions. This can be caused by several faults:

1. Failed Carriage Tachometer / Optical Encoder (Most Common)

The tangential carriage drive spindle relies on an optical tachometer (an IR LED and dual photodiode assembly reading a slotted disk) to tell the CPU that the carriage is actively turning.

 The Failure: The original IR emitter LED (OPE1 on the board) frequently goes open-circuit over time.

 The Result: The carriage starts moving, but because the CPU receives zero “slide tacho” pulses from the sensor, it assumes the transport mechanism is jammed and cuts power to the carriage motor to protect it, freezing control inputs.

 Fix: Replacing the IR emitter diode (a common modern replacement is the Optek OP240 or equivalent) on the spindle encoder PCB.

2. Servo Belt Slippage or Mechanical Binding

If the electronic sensor is fine, the carriage may simply not be moving smoothly.

 The Failure: Old grease on the threaded lead screw and guide rails hardens, or the small rubber servo drive belt has stretched/perished.

 The Result: The motor turns or slips on the belt, the carriage stalls mid-track, and the missing optical pulses trigger the same 2-second safety timeout.

 Fix: Clean off old oxidized grease from the threaded shaft with isopropyl alcohol, re-lubricate with fine synthetic oil/grease, and replace the carriage servo belt with a fresh, correctly sized belt.

3. LDR / Aperture Sensor Drift in the Control Panel

The manual transport buttons (⁠<<⁠ / ⁠>>⁠) work by moving a mechanical light aperture between a small bulb and photoresistors (LDRs).

 The Failure: If the photoresistors age or the calibration adjustment screws in the control assembly drift, the resting voltage fed to the control op-amp rises above the threshold (resting target is ~0.61V).

 The Result: The CPU gets confused by the unexpected voltage rise during automated movement and halts the carriage drive.

 Fix: Re-calibrating the aperture adjustment screws on the control board according to the Beogram 8002 service manual procedures.

4. CPU Board Solder Joints & Power Supply Capacitors

 The Failure: Cold solder joints around the microprocessor socket, edge connectors, or dried-out electrolytic capacitors on the main board causing supply voltage ripple.

 Fix: Inspecting the main board for cracked solder joints and performing a standard capacitor refresh if the deck is still running on original 1980s components.

• This reply was modified 2 days, 14 hours ago by Mark-sf.

[hcraig244]

Mark

Thanks for the detailed explanation above, your bang on with the LDR / Aperture Sensor Drift in the Control Panel being responsible for the issue….and following replacement of the lamp and both LDR’s (changed them out as I was in there anyway) as detailed above, the set appears to be working fine. I still need to set the carriage travel sensitivity, as I have disturbed the original setting during the work carried out, will need a cartridge fitting to complete this…..watch this space ;¬)

Craig

[hcraig244]

Ok….received 2 cartridges in the post, fitted one and balanced the tone arm to neutral then set it to 1.0 gram. With the platter drive connections unplugged I hit play….tone arm moved to the correct position and dropped…however the carriage refused to move forward when nudged inward…hit stop and the tone arm moved back to rest.

My view is that the tracking sensor lamp (like the << and >> manual operators) and possibly the LDR too has passed its/their best, tried again and this time measured the voltage to the lamp 14.68vdc…so good, concentrated on the adjustment screw and had some success….after several adjustments managed to get the unit to play over halfway through an album at which point it decided to stop and return to rest…did this a couple of times despite a number of attempts at adjusting the shutter….looks like everything else is functioning correctly however the lamp and as it will be exposed the LDR too will need replacing….the carriage isn’t moving forward every 2 or 3 rotations of the platter but will move forward after around 9 0r 10 rotations…clearly not good.

• This reply was modified 13 minutes ago by hcraig244.

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