Hello Lonnie,

yes, quite right...a strange measurement...that is why I tripple-checked 😳

1TR26 was one of my earlier suspects and has been replaced for that reason.

will need to check if I have a diode like the D26....tomorrow is another work day

i will be back.....

ALF

Hi ALF,

And while your working on it I'd check/replace 1TR20.

Regards

Lonnie

Hi Lonnie,

well, news are still not good I am afraid 😡

replaced as suggested 1TR20 and 1D26.....same result !

when I look at this I begin to wonder what else I can possibly replace that has not yet been replaced ??

now I am getting around -16.xxV at D26 which may be because of the diode change ?

looking again at 0TR1 there are 15V at the collector ......unchanged !

sure, I could replace that one again but.....? Would that change anything ....?

ALF

Hi ALF,

Rather than just replacing it again why don't you measure the voltages around 0TR1 to see if it is operating properly. It is biased on by 1TR18, so you want to measure the voltages around both. 

Since the base of 1T18 is grounded then for it to be forward biased the emitter needs to be at least -0.7V. If this is the case it will draw current through R78 & R77 which will cause a voltage drop on the base of 0TR1 which will forward bias it and you will have your 15V power supply. If 1T18 is not biased properly and you still have your 15V PS then either 1TR18 or 0TR1 could have a short. Measure the voltages to see. If all is measuring ok then you can move onto another area of the circuit.

Regards

Lonnie

Hi Lonnie,

it is not just replacing rather than precaution - desoldering components means additional heatstress - the last I need !

while I check/test those components I replace them with a new selected component.

If a test shows a faulty component I would have had the culprit by now but sadly, not so far 😕

i am aware, not always is a test conclusive and the faulty one could slip through.....me without knowing there was a problem.

but looking at the range of replacements, they are either all faulty or I/we are barking perhaps at the wrong tree ??

remember, starting with PLAY after hand-braking the platter everything seems fine....would that suggest that 0TR1 has a short ??

sure, I will measure again around those mentioned components and come back 🙄

ALF

Hi Lonnie,

the emitter of 1TR18 is about -0.63V  practically unchanged at PLAY and STOP/OFF.

yes, I have the 15V at 0TR1 which does not change, nor do emitter and collector at around 22V.

0TR1 definitely does not close !!

ALF

Hi ALF,

I opened up my BG 8000 to take some measurements:

At P6-4 on Standby = 0.76V, during Play = 0.076V

Collector 1TR21 on Standby = 0.067V, during Play 0.58V

So during standby 1TR21 is biased on and during Play it is biased off. A little different to how I thought it worked.

Your measurements of -ve voltage at P6-4 are an issue that we need to understand.

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Hi ALF,

The emitter voltage at 1TR18 is correct and 0TR1 will only "close" when 1TR18 is biased off which means the emitter voltage at 1TR18 goes above -0.63V. This will only happen when the -ve 15V supply is turned off. Things to measure and check:

Examine solder of pins P6 - 3,4,5 to confirm there are no solder bridges

Double check that 1TR21 has been replaced with NPN and is not in backwards.

Measure the CBE voltages of 1TR20 & 1TR19 during standby and play.

If you don't find any errors I'l lift the base of 1TR21 off the pcb and measure the output of uC pin38 during standby and play operations to see if it still puts out -ve voltages or if it puts out similar voltages to what I measured on mine.

Regards

Lonnie

Hello Lonnie,

interesting exercise....here is what I found:

                                         C.                   B.                       E

TR20   StBy/Play.     -18V / -15V.         0 / 0             -1.8 V / -1.5 V

TR19.  StBy/Play.    -17.4V/-17V.    -18V/-17.6V.     -23.4V/-23.3V

P6 - 4.      StBy / Play.     4.95V. / 4.88V.    Base of TR21 not attached to PCB !

no solder bridges on P6 found 😁

ALF

Hi ALF,

You need to replace 1TR20 (PNP) and I think you should also replace 1TR21 (NPN) at the same time.

Regards

Lonnie