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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

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