beogram8000 won’t turn on

[alf]

hi all,

just pulled one of my shelved BG 8000 off and onto the workbench….,its been a while…

it shows no standby dot nor any other sign of life. it has the 5VDC supply but i can not

verify the +/-15VDC  nowhere.

0TR3 = TIP32 is measuring about 25VDC ?? i previously checked 1TR18, 19, 20.

the BG had most of its caps replaced, incl the one in the uP box. the uP gets 5.06 VDC supply at P6-1…….

any other suspects I should check ??  all help is much appreciated as always

ALF

[sonavor]

Hi Alf,

You are on the right track in checking the power supply voltages.  Follow those voltages to where they stop.  Is the +5 VDC reaching PCB 2 ?  What is the output voltages of the regulators for +5 V, +15 V and -15 V ?

Check the PCB 1 connector pins where +5 V and +15 V connect from the chassis.

-John

[alf]

Hi John,

thanks for your input.

Looking at the circuit diagram, the +15VDC should be taken care of 0TR1/1TR18/1D25 and the -15VDC by 1TR19/1TR20/1D26.

the 5V regulator produces 5.06VDC which is also present at P6-1, so that’s ok.

As for the -\+15VDC I am only getting about +/-25.06VDC which is also present at P2.

it looks as I have to dig out TR18/19/20 and D25/26 for testing ?!

0TR1 = TIP32 tested ok with hfe=138.

ALF

 

 

[sonavor]

Hi Alf,

P2-2 should be close to +5 V, which you say you have.
P2-9 should be close to +15 V

1TR21 controls power on/off from the uC.  Check the voltages around 1TR21 and if they are not good then check for broken traces.

That PCB 1 board is very susceptible to breaks in the traces.  Especially at the bend in the board.  Every Beogram 8000/8002 PCB 1 board I have seen is bent (curved) from the way it mounts on the frame.  More than once I have had to jumper traces around the bend because of breaks in the trace.

This was a Beogram you had previously restored to working condition, right?

-John

[alf]

Hi John,

its been quite a while but from memory(?)  this was probably one I eventually shelved to be looked at again as other (easier) projects came in……

i know, that PCB is pretty terrible and not that flexible as it showed in various examples.

all those transistors I mentioned must have been tested off-board before but will be looked at again after I have taken out the board again plus without the Standby Dot present I would not expect to be able to turn on the Beogram anyhow.

will get back with further findings – thanks again for helping ?

ALF

 

[alf]

Hi again,

i have tested all previously mentioned transistors inc. D25/26…..all tested fine – that’s the good news but still no +/-15 supply.

P2-9 sees about 25VDC. That kind if voltage I see at 0TR1 as well, no surprise here.

I am afraid John your worst “fears” seem obvious: I found 1 cracked track so far but it is a very tedious undertaking to find more.

there is definitely a connection issue after fiddling with P2 the table suddenly sprang into action.

i tried to minimise the degree of bent in the PCB by slightly shifting the uP box backwards but sadly that didn’t have an impact in terms of restoring function.

looks very much like getting the magnifier glued to the eye ball again……..

there is no point replacing 0TR1 as it tested ok – i also did check for OL but nothing showed up so far……

will get back shortly

ALF

[alf]

Hi again,

so far I spend probably a couple of hours (incl. some needed breaks ) with various magnifiers to scan across the main board in search of broken tracks…….nothing to see !

going back to the elusive -/+15VDC search:

At the anode junction of 1D21/D24 I get about -25.3VDC, at the cathode junction of

1D22/D23 I get about +25.3VDC.

after having tested the involved TRs and Diodes to produce the 15V lines without any adverse findings I really have arrived  at a dead end …….!

what kind of AC voltage  should I see at the junctions 1D21/D222 and 1D23/D24  ???

unless the board has suffered a particular nasty almost invisible hairline fracture  it looks even more like another shelving exercise ?

so far only once very briefly have I been able to see  the -/+15 VDC by giving P2 a serious wiggle – that was when I suspected a connection issue but…., that is only good if it can be reproduced which I can’t , no matter what.

the usual question, where from here  -Shelf of Multimeter ??

ALF

[sonavor]

I would focus on the fact that you were able to get it working, briefly, by wiggling P2.
You won’t always be able to see a broken trace.  Check continuity between the related P2 wires/traces for where they came from and where they are going to.

In other words, see that the output of 0TR1 reaches P2-9 on the board.
On the board side check continuity from P2-9 to 1D25, 1C28 and other +15 V destinations.
Also check continuity around 1TR21 (wiring/traces to and from 1TR21).
Check that the grounds are good but it seems like the problem involves P2-9.

John

[alf]

Well John,

this one looks like a very tricky rescue. Frankly, I am running out of idea what else to measure or check.

sadly a repeated wiggling of P2 did not delivery a desired result.
The connection between P2 and 0TR1 is fine, all grounds checked fine as well as continuity between points of -/+15VDC and their involved TRs, Ds and Cs.

i understand there has to be a reason/source of the missing -/+15VDC lines. i even lifted the uP to make sure it sits properly in its socket – no impact.

whether the voltage of +/- 25VDC after the rectifier is fishy I am not sure.

fact is I have the 5VDC supply, P6-1 gets 5.06VDC which should make the uP happy.

a long distance analysis is always tricky and I really appreciate your input……just

-/+15 V would be nice to start ?

ALF

 

[sonavor]

Your +-25 V off of your bridge rectifier is good.  That is what you should see at those nodes.

How about continuity from 0TR1 collector all the way to  1C28 (instead of 0TR1 to P2-9 and P2-9 to 1C28) ?

Have you connected up a scope and monitored what is happening at P6-4 (the on/off control signal) or right at 1TR21 base?

John

[sonavor]

Just to clarify the problem…

Can you measure –

P2-8 to ground
P2-9 to ground
P2-10 to ground

– measure them twice, once at standby and once when pressing Play

Also do two measurements (Stby and Play) at –

1TR21 base to ground
1TR21 collector to ground
1TR21 emitter is connected to ground so other than verifying that connectivity, no measurement there.

John

[alf]

Ok John, here is goes:

Thank you for confirming the 25 VDC at the rectifier ??

continuity from 0TR1 directly to either -/+ of 1C28 is confirmed.

i did not connect the scope to either P6-4 or 1TR21: StBy or Play showing identical voltage of about 0.725 VDC when measured.

P2 – 8:   24.2VDC StBy= Play

P2 – 9:    21mV StBy,  16mV Play

P2 – 10:   24.2 VDC  StBy = Play

1TR21 B : 0.725 VDC / 0.720 VDC  StBy/Play

C :  49mV / 51mV  StBy/Play

E :  0 / 0 V  StBy / Play

P6-4 about 0.72 VDC

are these measurements providing us with some further pointers ?

ALF

 

[sonavor]

Hi Alf,

Your measurements at P2-8, 9 and 10 show why you don’t have +15 V.  The base (P2-10) isn’t turning on 0TR1 so +15 V is not enabled.

Your measurements at P6-4 and 1TR21 base don’t look right seeing how there is no change really between Stby and Play.  1TR21 is always on so +15 V is always off.

When the Beogram 800x is in Stby the uC is turning 1TR21 off via the control signal from 1IC1-38.  When the uC turns power on the control line goes low enough to turn 1TR21 off and allows +15 VDC to be enabled (via 1TR20, 1TR19 and 1TR18).

The source of your problems it appears is that the primary control, 1TR21, is always “OFF”.

Perhaps the Power On/Off signal from the uC isn’t able to reach the base of 1TR21.
Check the P6 connections.  That big connector can be a problem sometimes.  You might have to also check inside the uC (PCB 2) box for the integrity of P6-4 to the 1IC1-38 pin.

John

[alf]

Hello John,

many thanks for your clarifications.

please bear in mind the BG is missing its StBy dot in the display – so I am pretenting

the BG is in StBy mode when connected to mains.

there is definitive continuity from P6-4 to pin 38 on IC1, soldering looks good

and the measurement from P6-4 to pin38 of IC1 is exactly the same as from its flat band connector to pin38 at IC1.

continuity from P6-4 to Base of 1TR21 is verified.

whenever I press play the voltage of that signal remains basically unchanged from

0.72 VDC.

i know, what you are saying is correct but I don’t know yet why its happening.

are there any other potential players in the game ? I tested TR21 off-board ok, so is should not change things just by replacing TR21.

what voltage should I expect at P6-4 without pressing play and what when pressing play?

is it possible there is a issue with the keyboard ?? But The StBy dot should be present

with or without the keyboard connected, right ?!

ALF

 

[sonavor]

I thought you had a standby indication on the display.

Okay, if you don’t have a standby dot do you have the wire connected from the uC (PCB 2) metal box over to the single connection terminal on the small add-on board?
If your Beogram 8000 has that add-on board (“Control for uC”) then it needs that added connection wire.  If that wire is not connected then you won’t have a standby dot and the Beogram will not turn on.

John

[alf]

Hi John,

that black wire is & was connected. I just have reflown its connection points on the add-on board as well as in the uP box.

again, I briefly had the StBy dot, the table turned on when play was pressed with the carriage moving in a short distance but I could not turn off – I also briefly had the 15V supply.

it is obviously as you suspected a connection issue of a kind, just finding it. I do remember one of your comments from way back about the importance of the correct adjustment of the << and >> function (630mV?). anyway, there is more investigating to do.

Again, thank you very much for lending your expertise trying to help ?

ALF

[spassmaker]

Hi Alf

As John mentioned the black wire I remembered that some time ago I had an issue with one of these “Piggyboards”.

The Beogram was playing a record for a time and suddenly turned of, with no STBY Dot.

After deeper investigations it turned out that the Beogram sometimes just turned of completely with no STBY Dot visible. Even while playing or in STBY.

After poking around in the transformer and rectifier section and nothing obvisiously found I determined the small additional board which was implemented for a “saver uPC start” where the black wire, which already mentioned, goes to.

There are only a few parts on it but after changing the transistor and a few parts more the problem was not solved, maybe a carcked trace, I did not find out.

So I decided to extract the board and bring the whole wireing back into the state as the schematic shows.

The main PCB is not changed during the developing.

That did the trick, the Beogram had no dropout anymore and is playing still well.

B&O developer have implemented this board for a better uPC startup, but the older ones still live without that board, so what!?

In my eyes it’s not really necessary respectively I can’t find out.

I can remember that I found some information about the small boards somewhere in the www. but can’t remember where.

Maybe someone has these information and can share this here.

If you are at the end of ideas this would be one more possibility to try.

Regards

Christian

[alf]

Ok, back on the job but no good news so far.

in the meantime the 5V supply played up, getting up to 6V for reasons unkown ?

so far I have tried half a dozen 5V regulators and the best one delivers still too much

at 5.3V. The question I like to through into the round is the uP getting damaged or simply won’t work when supplied with 5.3VDC at P6-1 ?

I also ckecked 7TR1,2,3 & 4 – all tested fine. the uP connection to 7 P1 has continuity and I also  checked the ground connection to uP Pin 15 – all fine.

as John pointed out there’s still no turn on without the StBy dot which totally puzzles me.

is the uP faulty or is there something else fishy on the uP control board 7 like

7IC1 = CD4528 or 4098 ??

seriously, there has to be an explanation…….

ALF

 

[sonavor]

Hi Alf,

I still suspect a connection somewhere if the Beogram 8000 was previously working…rather than a bad microcomputer IC.

John

[alf]

Hi John,

i thought I actually did answer your question ??
Yes, the black wire to 7P1 is always connected.

i did reflow the connection at 7P1 and at the uP and there is continuity.

how likely is it though that the multivibrator chip on board 7 could have issues ?

as being the “controller” of the uP or did I get this wrong ?

i lost count how often I did check the various connections such as the P6 connector for instance and its two flat-connectors which to me sit rather “loosely” in that connector, slipping out quite easily. I very slightly altered its angle to make it easier for the flat connectors.

its been years ago when I purchased that BG and honestly can’t remember whether it was partially or not at all working – too long ago ?

i wish I’d know where this is going from here……..but not giving up yet !!

ALF

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