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BG8000 fuse issues

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ALF
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ALF posted on Mon, May 1 2017 7:02 AM

greetings all,

a new arrival, a BG8000, which had a partial re-cap job done by the previous owner.

I noticed C24 was put in the wrong way as its positive should connect to the F1 ?!

anyhow, I corrected that, completed the re-cap job incl C27 - see pictures - and now F1 is constantly blowing

even with my DBT ?

I checked D16 to D19, all measured ok.

did I overlook something ? any ideas or suggestions are most appreciated :-))

cheers

ALF


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ALF
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ALF replied on Sun, May 7 2017 4:03 AM

Hi Lonnie,

oh yes, the garden path......!

finally got to the new measurement:

voltage C27-  to TR17, P6 pulled, new fuse

E  showed 7.85V,  

B showed  7.12V

C showed  7.83V

yes, 0TR1 = TIP32 voltage regulator was the one I suspected to show problems ??

cheers

ALF

PS: out of interest, where are you located ?

 

Lonnie
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Hi ALF,

I'd leave 0TR1 for the moment, it won't switch on until you sort the power supply to the CPU.

There should be 5V at the output of 0IC1 and D20 the zener diode should hold it below 6.2V. Given that you measured 7.12V on the base of TR17 and there should be a 0.7V drop across D15 that would mean 6.4V on the output of 0IC1.

There also seems to be too much voltage drop in R75 so I'd pull TR17 and measure it. I'd also check D15.

Regards

Lonnie

(Melbourne)

ALF
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ALF replied on Sun, May 7 2017 1:20 PM

Hello Lonnie,

I did replace TR17 before as precaution - it is a BC557B transistor - and its reading of hfe=310 look ok.

D15 - which funny enough is not even mentioned in the SM ? - shows  a OL and 0.560 V readings according to its correct orientation. 

So I would cautiously say TR17 and D15 are not faulty - but these 5V must have gone lost somewhere ?

the question, what next ?

ALF

ALF
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ALF replied on Fri, May 12 2017 11:08 AM

Hi all,

I am really not quite clear about what is going on here:

with a new fuse installed, P6-pin1 pulled I can measure the following

TR17. Emitter 6.3V, Base 5.6V, Collector 6.3V

C28+ 14.97 V

D20 5.04 V as well as pin1P6

however, if I reconnect P6/1 the fuse blows........it makes no sense to me unless there is a fault in the processor box or is there not ?

If P6-pin1 shows 5.04 V with the connector pulled the fuse should be fine after reconnecting, unless....??

can somebody shed some light on this, please....

ALF

ALF
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ALF replied on Wed, May 24 2017 1:30 PM

Hi everyone,

here is a quick update of what happened in the meantime:

the fuse issue seems under control with voltage at P6/1 = 5.04V steady.

the +/-15V  are not quite there with +/-12.9V at the moment.

the following symptoms are interesting:

all connectors connected -

pressing TURN plattet spins but DBT illuminates, pressing STOP platter stops snd DBT is off.

pressing PLAY platter spins - far to fast ! - and carriage tries to move but returns only after a few cm movement, table does not switch off !

with P4 connector unplugged -

pressing PLAY  carriage moves towards the center but does not return, only > or >> can bring it back. DBT stays off.

I feel quite confident there are no soldering bridges nor any cracked joints !

I begin to wonder whether the uP is faulty ?

any words of wisdom from anyone ?

ALF

ALF
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ALF replied on Sat, Jul 8 2017 11:18 AM

Hello again,

found some time and motivation while waiting for parts to revisit the old BG8000 table with all its problems......

i resoldered the entire main board, so there should not be any source of uncovered issues remaining !

Same test procedure as before:

everything connected

- press 'Turn' and platter spins still too fast plus DBT lights up

- press 'Stop' and table turns off, DBT goes dark

- press 'Play' carriage moves over to 30cm record position, platter spins too fast and arm does not lower, DBT lights up

- press 'Stop'  carriage only moves back in small moves each time Stop is pressed. It only goes back to its resting position if '> or >>' is pressed.

I am still barking at the main processor as nothing else seems obviously wrong except the lit-up DBT when the platter starts spinning ??

sadly I do not have a spare processor to cross-check with........

anyone any ideas ... suggestions ?

pleeease

ALF

Lonnie
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Hi ALF,

To investigate the speed issue have you read the Beogram 8000 Technical Product Information pdf section 1-9 through 1-11? You can measure the voltage at the gate of 1TR26 to see if pin 2 of the integrator is correctly indicating a positive voltage since your RPM is too high. You can also check if 1D36 is working correctly to keep the positive voltage at no more than 0.7V. You can then work upstream or downstream from there.

Regards

Lonnie

Lonnie
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Lonnie replied on Mon, Jul 10 2017 12:54 AM

Hi ALF,

The voltage should be measured from pin 7 of the integrator not pin 2. 

Regards

Lonnie

Dillen
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Dillen replied on Mon, Jul 10 2017 7:18 AM

Check the tacho opto.
Check the CMOS 4013 in the tacho feedback.

Martin

ALF
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ALF replied on Tue, Jul 11 2017 3:37 AM

Greetings,

i

I can reproduce the signal at the collector phototranssitor/1IC1 pin 12 which is Sine-shaped

but at 1IC1 pin14 will not get the straight skirts but a triangular shape !

 

as for the CMOS4031 

red - to pos C28 - shows 4.95V

org - to P6/2 - shows 4.95V

green - to quarz - shows 2.2V

yellow - to P6/2 - shows 3.85V

blue - to neg C28 - shows 12mV

 

However the voltage at 1TR26/Gate  showed  -11.5V  and Pin7 of the Integrator 1IC3 showed  -11.6V

which is not good news ?!!

ALF

Lonnie
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Lonnie replied on Tue, Jul 11 2017 2:09 PM

Hi ALF,

Based on your CMOS readings of 1SD = Low, 1CD = Low, 1D = High you are getting a correct response of 1Q = High . Can you remove the input voltage, maybe by removing 1R50 or P4(7) and confirming if the output goes low.

Does your BG8000 have the additional board PC7 which controls the uC chip? From jpeg P1010309 it looks like it does. If CMOS 4013 is working correctly this board might be the next thing to check.

Regards

Lonnie

ALF
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ALF replied on Wed, Jul 12 2017 2:59 PM

Hi Lonnie,

my mistrust towards ICs has just had a "boost"

I had some suspicions about 1IC1, 2 and 3 and replaced those - the outcome was an improvement ๐Ÿค“

the previous signals in respect towards the speed sensor are now a sine and upright one corresponding to 33.33rpm.

however, there are more issues to deal with such as:

45rpm speed change is unavailable

carriage moves right across and does not return, only when 'stop' is pressed

arm does not lower with record present

so, in other words there is more investigation neccessary - I will look into that CMOS on board PC7 !!

ALF

Lonnie
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Lonnie replied on Thu, Jul 13 2017 1:34 AM

Hi ALF,

In your post it is not clear whether you have solved the high speed platter issue. You only indicate that the output of IC1 is a square wave. Can you confirm that the TT now holds 33.33 rpm?  If it does have stable speed then did the replacement of IC1 or IC3 fix that issue ie. did you replace them one at a time and measure the outcome? 

If you have stable speed then there is no need to check PC7 at the moment. The PC7 board was added to help solve a platter speed issue - see the bottom of 8-1 in the service manual. 

Regards

Lonnie

 

ALF
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ALF replied on Thu, Jul 13 2017 2:17 AM

Hello Lonnie,

yes, at the moment it holds 33.33rpm - I not sure though whether you would see a square wave signal at IC3 pin14 with a speed issue ?

I did replace the three ICs all at once but should have done it step by step.......

bear in mind I took over that table not working mainly for its transformer when I started investigating....

there are still issues as described such as:

- arm does not lower at record point

- carriage moves right across but does not automatically return, only when 'stop' is pressed

- speed change from 33 to 45 does not work

- gate of TR26 still sees about 3.2V which is way more than the suggested 0.7V ??

 

yes, I have all 3 service manal downloads ๐Ÿ˜Ž, read frquently through them trying to make sense out of it  ๐Ÿ˜‚

 

I like to rule out the main processor as the source of all those remaining  issues, as this would mean the end

of all further attempts to rescue the table due to its unavailability !

Cheers

AL

Lonnie
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Lonnie replied on Thu, Jul 13 2017 4:44 AM

Hi ALF,

 

For the 3.2V you measure at the gate of TR26 are you measuring AC or DC?

 

Regards

Lonnie

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