[alf]

Hi everyone,

just working on my BM8000 which just doesn’t want to start. I can hear and see 7RL2

working its guts out but just wont close. I have been following the connecting trail and it should get about 24-25VDC from P51-pin2 but I can only get about 19.8VDC !

would it be fair to suspect 6IC9 ?? Both relays are fairly new which should exclude them as the problem.

6IC9 = BD676 and the question is are these known to fail ??

I have gone over board 7 but all tested fine – both 10W 5.6Ohm resistors are fairly new.

looking forward to your comments and pointers.

thank you

ALF

 

[spassmaker]

Hi Alf

If you connect to mains is the “red dot” in the display lit?

Where did you measure the 19.8 Volts? Direct at the Relay?

There is a voltage drop via TR 18 as well so there won’t be 24 volt at the relay.

19.8 V should be enough voltage to engage the relay anyway.

Is the voltage dropping to zero after you heard the relay working?

Had already bad connections from PCB 6 to PCB 7 check also for bad soldering or corroded plugs and/or contact pins

How is the voltage on Collector of IC9 and IC10 ?

Steady about 22 to 24 volt after switching “ON”?

Follow the schematic until you reach the CPU, check the whole way via TR11, TR12, TR18, P48-5, P76-6, R55, PIN16 IC4 for bad solderjoints or breaks.

Same for the POWER ON route via IC9, TR2, TR1, TR4, TR5, P48-4, P76-7, R57, PIN16 IC4

Did you already renew some caps? Here speacialy C35 10 uF on the 5 Volt Regulator right hand on the heatsink, often the reason for some trouble

Regards

Christian

[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

 

[spassmaker]

Hi Alf

So if you measure 23.x Volt at 6IC9 there should be the same Voltage at P51-2 and at Relay RL2.

Measuring always with the same negative point.

Tis 23.x volt should be steady present after you plug the mains in.

The conection goes directly via P51-2 to the relay.

The other line to the relay RL2 comes from TR 18 via P51-1 to the relay.

Take a look for these connections and mesure at the Collector of TR 18

Check the voltage on P48-4 (ST BY) and P48-5 (RELAY ON)

Both should be LOW when the amp is switched on.

Regards

Christian

[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

[spassmaker]

Hi Alf

Sorry maybe we missunderstood…

and Sorry but I ran in a wrong way to say that the 23.x voltage should be present after connecting mains, not right

The voltage is caused by 0 volt at P48-4. Comes from uPC PIN14 “ST BY”

As you wrote:

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

I thought that you measured 23.x Volt at collctor of 6IC9.

Is the voltage on C33 and c34 ok? (about24V) also at Emitter of 6IC9 and 6IC10

but anyway there should be 5 volt at P48-4 and 5 volt at P48-5 in “St By” mode.

If you connect to mains there is a short “klick” right?

 

55 Volt are comming up when RL 2 is engaged, a short “klick” would not be enough to charge the big Caps c3 and c4.

The 55 Volt is used for the delayed relay circurit.

is the amp responding to any pushbutton?

[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

[Dillen]

The rush-in current at power up is quite substantial. Not all voltage converters like that.

A dead prescaler usually won’t affect the function of the tuner. It would merely mess up the displayed frequency.
Check the cables to the tuner boards, at least the screened one that goes to the CPU board
is easily pulled off inadvertently.
Check also the solder joints at the two tuner boards interconnecting plugs.

Martin

[Glitch]

alf: Are your startup issues resolved? If not, I’ll have one of my BM8000’s on the bench within a few weeks for a full recap. I can capture some scope traces of the start-up procedure if you think that it would help you. Let me know.

One thing that I noticed about the BM8000 is that the receiver is sensitive to startup conditions. Both of my BM8000’s start normally when plugged directly into an outlet. Neither of them will start when I run them connected with a light bulb (current limiter) in series.

Glitch

[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

 

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