[alf]

Sorry but the multimeter does not lie !

I measure incoming mains voltage which is 244 VAC .

what I can measure across P1 pin 1 to 2 and pin 3 to 4

are about 0.015 to 0.020 VAC and that is the sad fact.

I still believe that powerpack (transformer) is not working as it should, in fact

It probably died a slow death ?!

luck had it that I was able to purchase a replacement one from the UK….so it will take a while till Work can resume.

ALF

[alf]

Ok, another voltage check:

looking at the disconnected transformer and its Plug1 voltages

Pin1/2/3/4 = 42 VAC

looking at the connected to board3 via Plug1 – Plug2 and 3 were disconnected !

pin1 = 5.6 VAC, pin2 = 5.5 VAC, pin3 = pin4 = 0.08 VAC

I do not get 5 VDC nor 22 VDC

grounding Plug2 pin2 via neg of C3 delivers nothing (unless I misunderstood you)

are you still quite confident the transformer is ok ?

ALF

 

 

[alf]

well, I believe my last measurements were measured correctly.

I can not imagine the deck to work with these kind of voltages, can you ?

there is still the unanswered Q :

is the powerpack (transformer) working according to its specification ?

i checked basically all components on that power supply board (3) without any

further defects.

ALF

[alf]

The AC voltages as you suggested are around 0.018 VAC P1 1 to 2 and P1 3 to 4

when the transformer is disconnected from board 3

does that make sense ! Sorry about the confusion

ALF

[alf]

Thank you very much for trying to help – much appreciated !

i really don’t know what the current draw is or should be in that circumstance.

the way I tested or checked was to isolate a possible transformer issue from the rest of

the deck by unplugging P2 & P3 which are supplying the rest of the deck, in other

words the only connection from the power supply to the main deck.

so, it is really only the power-pack (transformer) connected to board 3 which should

deliver the 5V, 14.8 V and 15.5V supplies for the deck but it doesn’t.

there one last thing I will try and report back.

ALF

all main components involved have been tested off-board.

[alf]

As another check I disconnected P2 and P3, which are the supply lines to the deck.

so I must ask again:

what makes the transformer secondary AV voltages almost “evaporate” when

that transformer is connected to board 3 where its AC voltages are getting

rectified to DC ? Which load exactly is there ?

just like to understand – thank you

ALF

[alf]

Well amongst many things I do not understand this is certainly amongst them:

the transformers secondary delivers AC voltage to the rectifier diodes….so how can that be this AC voltages can be lower before DC voltage is supplied to the rest of the circuit?

so, lets assume there are 40VAC delivered to the rectifier, turns into 5 VAC before getting rectified ?? Sorry, don’t get it.

the transformer’s fuse blew as well.

looks like I am missing something here, or do I ?

ALF

[alf]

I had another check at the transformer and its connection to board 3:

It secondary pins show AC voltages of up to 40VAC when disconnected from board 3, but all those voltages seem to break down to levels of 5 VAC and less the moment the transformer is connected to board 3 via P1.

so, is this transformer faulty or is it a plausible reaction because of a problem elsewhere?

bottom line is : the deck does not work

ALF

 

[alf]

I would not call this working – when play is activated the display comes on for a few seconds and a very faint click (as something tries to engage) is heard…then came over, display out, nothing further……

as mentioned earlier, feels like a protection is kicking in ?

quite obviously something is shutting down the deck very quickly.

ALF

[alf]

I checked all components in question off-board:

C9 = 21uF, TR3 and TR4 all hfe near 290.

I wonder if the protection kicks in as the deck shuts down shortly after play is activated because of a different fault elsewhere or too sensitive ??

ALF

[alf]

Obtaining those voltages was a bit tricky because the deck shuts back to standby

fairly quickly after PLAY was activated:

TR1: B = 5.8 VDC, C = 15.8 VDC, E = 5.3 VDC

TR2: B = 15.8 VDC, C = 5.9 VDC, E = 16.1 VDC

are these voltages consistent with proper functioning transformer ?

ALF

[alf]

Well, back on the BC7000:

sadly no change after replacing LM272 – that drawer motor worked fine before.

i replace the BD435 with a BD437 but what I can not get is the 12V supply for the capstan motor.

the fuse resistor has also been replaced !!

as said before, the motor works as been tested with my benchtop VDC supply.

i begin to wonder if the transformer got a hit during the “accident” ? It would be good

to know what its typical VAC voltages are before hitting the rectifier diodes ?

other than that I am stepping in the dark right now without progress.

just such a shame that lovely deck doesn’t work.

anyone, anything ?!

ALF

[alf]

The following parts are gone:

uP board, display board, big alu cover – anything else is available ?

ALF

[alf]

Right ?, just been there…nice shop.

good to know the BD437 would work – I can get that one even here.

the l272M are most likely chinese origin, sold in the UK, US and of course CHN

the order is out !

ALF

[alf]

I look into it, but first I have to restore the 14.8VDC supply.

the L272M mot control could still be fine but without the supply I couldn’t test.

the BD 435 has to be ordered, unless I could use a BD437 as alternative ??

the same question is in regards to an alternative for the no longer available

L272M chip ?? Any suggestions ?

ALF

[alf]

Yes, the safety resistor was dead and has been replaced.

sorry, I meant of course 22VDC !!
Correct, the 27-28VDC are in Stand-By – ok, thats cleared up….when play is activated

i get just under 22VDC.

still missing the 12VDC for the drive as well as the 14.8VDC at P6-pin9 ??

i had the motor running on 12VDC with the benchtop power supply – no trouble.

difficult to imagine the motor is at fault.

i will look into the BC-435 and BC-136…other than those will cause a headscratch.

ALF

 

[alf]

Hi Martin & Glitch,

thank you for helping out – sadly my BM has turned into a salvage operation……

to explain: I had indeed solved the start-up by using a much more suitable AC-AC adapter providing 120VAC instead of the ordinary step down, delivering only 110VAC, with a defacto output of only about 100VAC.

after reassembling I noticed no tuner signal – all the preset stations were still on display but no sound …… I verified all plugs / connections are properly connected which was the case.

one fatal mistake occured – I forgot to put back that insolating cardboard protector which sits over the small stand-by transformer. Putting all down, obviously something touched where it shouldn’t – all hell broke loose, smoke coming from the power transistor assembly…….the end ?

so, whats left for me to do is to check what I can salvage – very sad, that BM had a full recap !!!

once again, thank you all for stepping in and offer to help – very much appreciated.

ALF

 

[alf]

Hi Christian,

just had a suspicion the BM may actually not getting the required VAC ?

it is a US model, type 1903 (120VAC !) and its been operated using a step-down transformer (110VAC output).

that BM had always had some trouble with the start-up and so far it worked just ok.

i decided to measure the actual VAC it is getting, showing only about 97VAC.

using my variac and cranked up the mains voltage to about just under 120VAC…..and

surprise – no trouble with the start up ! It is a power-hungry beast. So I used my other AC to AC adapter which is delivering 120VAC output.

right after reassembling I noticed the tuner “is gone”, meaning it wont pull any stations

in ?? Of course I checked all connections, nothing suspicious to detect.

could that pre-scaler chip have died in the process ?? The other inputs work.

regards

ALF

[alf]

Hi Christian,

no !!

i do not measure 23.xVDV at P51-pin2 but just under 20VDC, same as at the 7RL2

the voltage is only present when I try to start up the BM – it is not present by just connecting to the mains.

same appears at 6TR18-C – at start up I see about 20.xVDV.

interestingly enough I can not find +/-55VDC either ??

nor can I verify the voltages at P48 in ON status as the BM does not switch on !

ALF

[alf]

Hi Christian,

the red dot is present.

the 19.8VDC were measured at P51-pin2 connecting the 7RL2 directly.

At this point I should see at least 23.8VDC as per circuit diagram – should I not ?!

just taken out PCB6 and replaced BD676 with a higher Hfe reading than the old one.

have not checked the other points. The BM has seen a complete recap !!

the voltage at 6IC9 – collector is about 23,x VDC – have not yet checked 6IC10.

will get back with more findings…..

ALF

 

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