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Beomaster8000 repair/resoration

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ALF
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ALF posted on Thu, Mar 21 2019 8:53 AM

greetings ALL 😁

I decided to start a new thread with my new donor-unit BM8000 - this time in the correct forum !

this donor unit was purchased as a parts-reservoir but turned out in very nice cosmetic condition.

so I took a close look and noticed all boards were recapped, the displac is fine....well, so far so good.

further testing reveiled there are issues:

Plugged in it shows the StBy dot.

turning on, no relay clicking while the display comes on.....hmmm ?!

checked the power supply board....all associated transistors have tested fine off-board, all caps are in the correct way, all connector joints have been reflown.....?!

next thing I noticed the small heatsink with the 3 voltage regulators is getting VERY warm....?

next thing : with no relays energized I can measure the 15V and -15V regulator which should only be possible

when the start-up circuit gives the “green light”.

5V should be present at Pin14 / 9IC4 during STBY mode and going down to ‘O’ when ON is achieved....no, it remains at about 25mV

meaning: the BM according to this is actually out of ST BY !!

5V are only present at the 5V regulator when I disconnect P76 of the processor board ?

a faulty processor 9IC4 ??

I did change the two 2MHz crystals (as suggested as a precautional measure by Beolover) after removing 

both uPs for safety reasons......! No change !

I disconnected the keyboard in case the on/off key is stuck and used the remote to turn off/on  the BM....

no luck here either 😡

disconnected P51 and 50....no change.

well, what am I missing here ?

and this is only unexpected work at the donor-unit while waiting for those speaker switch replacement to

continue work/repair/restore on my original BM8000 project...😳

guess help is badly needed here 🙄

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ALF
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ALF replied on Tue, Mar 26 2019 12:18 AM

MANY thanks Lonnie,

I ordered the one you suggested - I wonder if that would be suitable as a RL1 replacement as well....just in case ?!

will report back with further progress.

best

ALF

ALF
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ALF replied on Tue, Apr 2 2019 10:36 AM

Ok,

back on the project:

it turned out both of the old relays RL1 & 2 were dead. Today was the big day .....well and truly !

two new Shrack relays in.....and both relays clicked 😁. Nice, but short lived !

after adjusting the no-load current and connecting two speakers the BM suddenly disappeared in a cloud of stinking smoke coming from board #7 - the start-up circuit ! 😡😡

what happened was C1 - the 330nF/275V cap - blew up in smoke - a miracle the smoke alarm wasn’t triggered.

now, the big question is: was this cap pre damaged and could not perform the intented task (as both relays were dead to begin with, reasons unknown)

or is there another likely cause ?

that cap seems difficult to find, unless I order 5 or more, which is a small problem in the scheme of things.

Could I risk a 470nF / 275V cap for the job as well or is this similar to changing a fuse for a higher spec one - an absolute NO !

Any thoughts from the crew of experts ?.......the uP still tests ‘OK’

thank you

ALF

ALF
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ALF replied on Tue, Apr 2 2019 11:01 AM

Well, an additional question for 7C1 replacement would be:

Kemet paper cap or Polypropelene cap ??

ALF

Dillen
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Dillen replied on Tue, Apr 2 2019 12:15 PM

The two relays are not identical!

Martin

Dillen
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Dillen replied on Tue, Apr 2 2019 12:17 PM

The suppression capacitor MUST be a Class X!

Martin

ALF
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ALF replied on Tue, Apr 2 2019 12:31 PM

Thanks Martin.....just what I suspected !

can you recommend or perhaps suppy a suitable one for 7RL1 ?

thanks

ALf

ALF
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ALF replied on Tue, Apr 2 2019 12:33 PM

Understood ! Thanks for clarifying that  for us.

most helpful 😁

ALF

sonavor
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This is an interesting issue. I have only replaced these 7RL1 and 7RL2 relays one time and I did it by changing the relays from one Beomaster 8000 spare unit to the one I was repairing. I didn't pay attention to the two relays as they looked the same and I replaced 7RL1 to 7RL1 and 7RL2 to 7RL2. The Beomaster service manual does list the two relays with separate B&O part numbers -
7RL1: 7600053
7RL2: 7600060

I have never found any specifications on them.

Today I opened up one of my spare Beomaster 8000 units I haven't got around to restoring yet. I took the two relays out for examination.
Here are a couple of pictures.

They look identical but you can see the manufacturer markings are different numbers - BV 1004 for 7RL1 and BV 1044 for 7RL2.

7RL2 had a sticker with the number 2375005 on it.  I also see a number -  802105 embossed on the 7RL1 case. No number embossed on the 7RL2 case.

I measured the coil resistance on both relays and they are the same (around 980Ω). When I get a chance this evening I will checkout their switching voltages.

If anyone has spec sheets on these two relays it would be appreciated.

John

 

 

 

 

 

sonavor
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Hi ALF,

I found this relay: Omron G2R-1A-E-DC24
It has a maximum coil voltage rating of 170% of the rated 24VDC coil voltage.

That will handle both the requirements for 7RL1 and 7RL2.
Looking at the Beomaster 8000 startup circuit schematic

The 7RL1 coil voltage can be over 24VDC so the 170% rating of the Omon G2R will work for that. The 7RL2 relay coil should be 24VDC.

John

 

ALF
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ALF replied on Wed, Apr 3 2019 1:02 PM

Hi John,

so much work has gone into this.....thank you very much 😁🤙

glad I threw up something interesting for our readers & followers.

does that mean Lonnie’s Schrack relay choice should not be used as a RL1 replacement ??

i noticed the different B&O part numbers in the SM but as you mentioned....in the absence of any further info on the parts......!

a quick recap:

after measuring open coils on both the old relays, something that appeared to be the reason for not getting energised I used two of the Schrack relays.

that seemed fine as both got energised after turning the BM ‘ON’. 

What worries me is the fact that after connecting the speakers (co-incidence I wonder ??, unrelated perhaps ?) 

suddenly the supression cap 7C1 got destroyed smoking madly !!

i believe the “fire” was contained to the start-up board.

now the chase is on for the OMRON relay.....and then we shall see what happens next ?

ALF

sonavor
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Hi ALF,

The 7RL1 relay can see more coil voltage than the 7RL2 relay. The coil resistance of the relay is a factor in that. Without any spec sheet on the Schrack relay we don't know what the maximum coil voltage can be. We have the Omron spec though and it shows an 1100Ω coil resistance and a maximum coil voltage of 170% of the rated coil voltage (which is 24V). So the Omron will handle up to 40.80VDC. The voltage across 7RL1 should be less than 30VDC.

John

ALF
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ALF replied on Tue, Apr 9 2019 1:03 PM

Hi John,

work has resumed, the Omron relays are installed as well as a new 330nF suppression cap - I ordered the same typ as seen in your picture, class X2.

while waiting for the paper caps I got hold of a metallized/polyprop class X2 / 330nF cap, which is also used for the same purpose - should I go back and reinstall the original paper cap type instead ??

all relays are getting energised and nothing has gone up in smoke yet 🙄, however the same issue seems to haunt me: where is the volume ??

repaired the vol-wheel assembly and resoldered one of the short ribbon connectors from the control panel (common prob)

by turning the vol wheel I can see the display changes the indicated levels but I can only get a very soft sound when its up to almost level 6 ?

tried both speaker terminals - no luck. Speaker switches move freely as well.

no-load current and DC offset have been adjusted as per SM on both output boards. Must try the headphone output to see if that works ?!

in one older thread I noticed one member changed the AD10/192 switching IC for a AD7512 chip........also having issues with the volume.

it may have been slightly different from the problem my BM displays.....perhaps a lead if that device is blocking the full signals.??

i did try to use the TP2 input, feeding a sinewave signal from my iPad.....nothing has come through or was audible !

feels like I am moving in circles.

i’ll be back !!! 🤬🤬

ALF

sonavor
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Hi ALF,

I still suspect the volume circuit on the filter and tone control board but to isolate that I suggest taking the preamp board from your other Beomaster 8000 and swapping it in this one. If the problem is the same I think you can eliminate the preamp and those multiplexer devices. If the problem goes away then you just have the preamp board to deal with.

Assuming the preamp is good, you are left with the filter & tone control board. You verified the volume control IC was getting signals from the microcomputer board and the volume display functions. That leaves the volume control circuit or a faulty connection (cable/connector) somewhere in the path. 

John

ALF
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ALF replied on Thu, Apr 18 2019 8:56 AM

Hello John,

finally found some time to undertake some further testing:

sadly both BM8000, which are currently in intensive care displaying the same volume behaviour.

one of them had the volume attenuator chips on the tone/filter board replaced but the same issue....?

I checked again the logic-table for MSB and LSB according to the SM and both, P28 and P29 are getting the correct signals!

I even tried a replacement chip on the tone/filter board : AD7512  for  AD10/192 ...same issue !

that is totally wheird, unless those AD7110 attenuator chops are fakes and the original ones dead.

there are no problems with the connections....at least not that I can verify one.

back to work.....

ALF

Dillen
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Dillen replied on Thu, Apr 18 2019 10:02 AM

If you can provide photos of the ICs we can most likely tell you, if they're fakes.

Martin

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