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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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this shows the polarity marking of C24 on the board quite clearly !


Lonnie
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Hi ALF,

I presume it is the fuse on the main board and not the one inside the transformer that you are talking about?

Can you confirm that you are using an 800ma 250V  quick blow fuse?

Does the fuse blow as soon as you switch the deck on or is it at a later stage of operation?

With the fuse blow have you checked to confirm that the +/- 15 v power supplies are ok?

With the fuse blown are you getting a reasonable voltage at C24 and the ripple looks ok?

Have you checked the D20 zener to confirm it is not shorted?

I'd then isolate 0IC1 to confirm it is operating properly at 5 volts.

 

Regards

Lonnie

sonavor
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Hi Alf,

You can't always go by the board markings. Your C24 is installed opposite of what it should be. Here is a picture of Beolover's Beogram 8000 and my Beogram 8000 project from a while back. You can see that C24 has the negative lead on the side facing the large C27 capacitor.

John

Dillen
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The board has holes for mounting both ways!
Often confused.
It looks fine.

Martin

sonavor
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Update - I see your problem Alf. I believe you have C24 in the wrong solder holes. Here is a picture of the main board trace side from a recent Beogram 8002 I restored. C24 isn't where the board markings are. It is as shown in the picture. The C24 positive lead does go to the fuse as you expect but the negative lead connects to the negative lead (and ground) of C27.

 


sonavor
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Dillen:

The board has holes for mounting both ways!
Often confused.
It looks fine.

Martin

Yep, I see that now too.

John

 

Dillen
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There's a negative pad on each side of the positive.
Note the jumper!

Martin

sonavor
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Yes. If the capacitor had been in backwards it probably would have let him know Smile.

John

ALF
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ALF replied on Wed, May 3 2017 11:06 AM

hi lonnie,

I used a 1A /250V fast fuse  instead of a 800mA one - no other was at hand at the time,  the correct ones are now on order !!!

what happened was :  the display went dark, nothing was moving......the only reason for that seemed a blown fuse, which was the case !

yes, F1 on the main board.

I get about 14.3V at C24+ and 23.6V at C27+

D20 is fine.

but: fuse still blows, nothing is moving, no motor no display !????????

ALF

ALF
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ALF replied on Wed, May 3 2017 1:31 PM

Hi john,

good to hear from you again 😁🤗

I actually purchased that table for its transformer, noticed the partial recap job but it was not working.

under close inspection I took the time to finish the recap job as the table is in quite nice condition.....nothing broken, nothing missing.

all connector joints have been re-soldered to exclude cracked joints....

sadly it did not work out - after carefully re-checking for correct polarity of all caps the display went dead and nothing was moving - plus a blown fuse,

which explained.......

i could measure some voltages but do not understand the absence of the 5V and 15V ?

perhaps I should just be happy about having secured a good transformer ?!!

ALF

sonavor
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Hi Alf,

Which F1 fuse blows? The one in the transformer box or the one on the main board? They are both designated "F1" Smile.

John

sonavor
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Nevermind...I just read and found the answer two posts up.

Lonnie
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Hi ALF,

 

OK, you have voltage at C27 but in the above post you have indicated an absence of 5 & 15V.

Can you measure the voltage at C28?  It should be +15V.

Can you measure the voltage at the anode of D26? It should be -15V.

Can you isolate 0IC1 by lifting R75, adding a new fuse back in and removing connector P6. Measure the voltage at P6/1, it should be 5V. The D20 zener and the F1 fuse are designed to stop anything higher than 6.2V  getting to the microcomputer. The fact that the fuse is blowing could indicate a short or too high a voltage?

Regards

Lonnie

ALF
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hello Lonnie,

I can measure about -12.6V at C28,  -26.6V at D26 anode

P6/1 shows -5.7V.......

all voltages are negative, which is very odd ???

ALF


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