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Beogram 8000 speed and muting issues

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ALF
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ALF posted on Mon, Feb 27 2017 12:43 PM

greetings all,

1. my BG8000 showed some speed problems with the platter just spinning at high speed - but nothing stopping it ?

at the same time the first two speed-digits - 33 and 45 - flashing when selected ??

all electrolytic caps have been replaced not so long ago - ALL !!

tacho disc - a metal one - is new !

first attempt was to re-solder all joints at all connectors as well as the joints to the uP - no luck !

2. unrelated, but a problem seems to be the muting:

when the carriage moves across to the 30cm record position the output signal should be muted as the tonearm has not been lowered yet - but isn't muted, as I can hear the stylus brushing over the cleaning brush - same on the carriage return - not a nice sound !!

checked 1D11 - ok ! checked 1TR7 BC-547B - ok ! defect muting relay ?????

the speed problem was present at the beginning but somehow cured itself  and the table played without that issue.

the muting problem was there but as it was annoying enough I finally consulted the SM !

can someone shed some light on these issues - and yes, it could be a faulty uP, but......is that the only option?

thanks guys

ALF

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ALF
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ALF replied on Wed, Mar 1 2017 3:36 AM

Just a quick update

the speed issue has gone again for now !!

my money is on the speed sensor having an intermittened fault ??

all I did at this point was applying some heat at its solder joints.

perhaps not a cure in the eyes of our purist-expert-repairers...... so far so good, but

where could I get a replacement part except from a "for parts only" unit ?!

as a side issue - but important - I resoldered all connector joints on the main board !

as for the muting issue:

still not fixed !

the muting relay klicks but that may not neccessarily mean it works due to perhaps burnt or

dirty contacts ?

time to change the relay ?   tas a percaution I resolderedhe relay's joints.it is an issue I could live with, although it would be nice to have it sorted ?!!

should someone have any better ideas - please don't be shy

thanks for your suggestions

ALF

 

ALF
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ALF replied on Wed, Mar 8 2017 4:55 AM

Well,

no takers ?😳

Anyhow, I am not too worried about the muting issue, just took out that little dust-brush instead of 

spending endless time investigating that issue further as it really doesn't do any damage!

as for the speed issue I might withdraw some money to put it on the uP !!

this uP gets fairly hot after some time and that "over temperature" may cause that speed issue ?!

apart from the previous suspect the speed sensor the processor replacement is hard to find and still a gamble !

in case of any other findings I will get back !

cheers

ALF

dbxdx5
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dbxdx5 replied on Wed, Mar 8 2017 12:06 PM

I was having the same muting issue with my 8002. Turned out it was the relay. From looking at the service manual for the 8000, it appears that it uses the same model relay as the 8002. The replacement I bought is Omron G5V-2-DC12. 

ALF
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ALF replied on Wed, Mar 8 2017 12:39 PM

Thanks for the relay info - much appreciated 😲

As for the main processor I am not very optimistic finding a replacement any time soon ?!

cheers

ALF

Dillen
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ALF:

Thanks for the relay info - much appreciated 😲

As for the main processor I am not very optimistic finding a replacement any time soon ?!

cheers

ALF

As I said previously; For your own good - stop guessing and start diagnosing.
It's almost surely not the processor.
More likely to be some other component in the speed regulation circuits or an unstabile power supply.
The processor will be about handwarm, and the heat transfers to the metal housing, which will also feel warm after some time.
If it's HOT something is seriously wrong..

When above you said, that the reverse spinning problem "went away", it still indicates that something is amiss.
Perhaps a cracked solder joint or a broken copper trace. Both can be incredibly difficult to locate, even with a scope.

Martin

ALF
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ALF replied on Thu, Mar 9 2017 7:13 AM

Martin,

for your information: the platter did nor does it spin in reverse but occasionally much too fast !

this seems to happens after an hour or so of using it ?! To pin-point how long exactly is difficult.

I spent hours inspecting the joints on the boards - i just do not have an x ray machine but I resoldered

a substantial number of joints incl. all connectors.

as you would know a complete cap change has been done before - the tacho disc is a new metal one !

and what you also  know is the difficulty of tracing intermittened fault behaviour - in regards to a possibly faulty speed sensor nothing is certain !

and if it is it is meaningless as they are no longer available (as far as I know).

leaves the muting issue, which is now down to the muting relay ?!

for some it is the destination rather than the journey and mine is a working B&O component 😸

ALF

sonavor
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It sounds like you could have a heat problem. Just guessing but how are you currently running it while testing? Is it running with the Beogram open (including the metal box where the processor lives)? I found it is worth having an infrared temperature gun like the air conditioning technicians use. Monitor the temperature of the processor to see how high the temperature gets and if it is constant. Make sure you have the heatsink installed on it. Also monitor the DC power to the processor and see if it is stable.

Post some pictures of your test set up too.

John

ALF
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ALF replied on Sat, Mar 11 2017 3:12 AM

Thank you for your concerns John - good to hear from you again 😸

I re-applied the heat-sink paste on the main uP to make sure it has good contact with the metal cage.

most processors get reasonbly warm, so it makes sense to ensure a good heat transfer.

this table is somewhat harder to work on - not like the early BG.

at the moment it plays nicely and the only issue remaing (for now) is the muting one. i will replace the old omron relay.

so, how do you trace a fault when none is present but I take your point of finding a way of monitoring the uP dc-supply.

as you make have red already I did spend quite a bit of time with visual inspections and a lenghty re-soldering job,

meaning I like to rule out any dry or cracked joint issues.

Martin claims it is most likely not the uP but possible issues in the speed regulating circuits.......fine

but who could provide a speed sensor replacement if..........?

anyhow, I will stay with it, however other projects are claiming my time right now like a  still not working BM4400 and a

new BM4000 in absolute stunning cosmetic condition - only one channel working at the moment 😪

kind regards - always good talking to you

ALF

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