Hi Lonnie,

replaced without the desired outcome 😡

I feel like simply integrating a hand-switch in the mains cable and live with it ?!?

what else is left that would make sense to replace ? Unless my peak tester lies, is faulty or all replaced transistors were fakes 

there isn’t much I can do about it. 

Is it really that far fetched to suspect the uP ??

I played a record this arvo and the deck performed nicely minus of course the never stopping anti clockwise spinning platter after record play-out stop......!

I can not think of another fault source, can you ?

All transistors are put in the correct way, no mix ups between NPN and PNP....no solder bridges and no detectable broken tracks.

I have to trust the DMM readings, what else can I possibly do.

ALF

Hi ALF,

I'm not giving up on the uC just yet. If you notice the difference in the voltage output between Standby and Play it is the same difference as mine just offset by about 4.8V.

Did you put new parts in or just measure the old parts and put them back in? If you put new parts in did you remeasure the voltages around 1TR19, 20 & 21 and did they change at all?

Regards

Lonnie

Hi Lonnie,

this is the outcome after replacing TR19/20/21.....all tested new transistors !!

                                                    C.                      B.                      E

TR19.     StBy/Play.       -16.3V / -16.1V.    -16.8V / -16.6V.  -22V / -21.6V

TR20                              -16.9V / -16.6V.    -3mV / -26mV.    -0.9V / -0.6V

TR21.      StBy/Play.         Oscillating             Oscillating        -3mv / -15.9V

as you can see the values are slightly different from the previous table.

ALF

Hi ALF,

How can the emitter of 1TR21 be at -15.9V in Play mode. It is supposed to be grounded? Is there a ground problem at the emitter?

Regards

Lonnie

Hi Lonnie,

apologies, my mistake....it can get confusing after a while 🧐

emitter in StBy = -3mV and in Play = -26mV

in the meantime I double checked the soldering in the uP box, as well as the uP legs after replacing the socket.....all fine !

too easy to break one of the 40 pins while inserting the chip.

can we really rule out a uP problem ? It just makes very little sense after all those parts have been replaced, not only once but twice !!

did you by any chance do any ohm measurements at SO1 in open and closed position ?

well, where do we go from here ?😳🤯

ALF

The interest in this problem has been absolutely fantastic with over 1500 views.....but still no solution......amazing?!

as said earlier, sensible cautious replacements did not deliver plus all the help has not been rewarded yet☹️

All tracks involved in and around Power ON/OFF are fine, verified with ohm measurements, components involved have been tested

is it really the uP not playing ball ?

I am aware of earlier replies more or less ruling out the uP,  the number of TRs, Cs, Ds are finite.....no cracked joints....!

“Who can it be now” to quote Men At Work ???

ALF

So you verified that the microcomputer IC is sending a drive command to the platter when it is supposed to be in standby?  Start at the platter drive (P4-1, P4-2 and P4-5) and see what voltage is there when the Beogram says it is in standby mode.  Then trace back to what is generating that voltage. There has to be a stimulus to the motor drive circuit. 

Hi ALF,

Before you move on from the electronic switch that manages the power supply I'd verify it's working properly by manipulating it without the uC. I'd lift the base of 1TR21 from the PCB and hook up a small circuit with a 1.5V battery and a 2k, 1.8k & 200 ohm resistor and tap voltage at 0.75V and 0.0075V and use a switch to bias 1TR21 on and off and confirm that the +15V & -15V supplies go off and on.

Looking back a few pages ago John asked you to measure the voltage at P6-10 to see if the voltage goes to 0V when the arm goes back to rest position. I didn't see a response from you. Did you make a measurement monitoring the SO switch?

Regards

Lonnie

Hi Lonnie,

sorry, somehow I overlooked that....

P6-10 is on 5V in Play mode and goes down to 25mV in Standby

will attend those other pins at P4

ALF

Also...read Beolover's Blog post on the brake circuit and how he was able to make the platter drive in reverse.  In particular - "The 'reverse drive' aspect of the brake system can be seen by a simple test: Connect the base of TR31 to ground with the unit in standby and the platter starts spinning backward!"