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Beomaster 8000 Restoration

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dahiyas
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dahiyas posted on Tue, Oct 13 2020 5:47 AM

This weekend I started on trying to restore a Beomaster 8000. 

Couple of issues before I started -

1. Three buttons missing on the panel - Martin found the replacement buttons in his dungeon and sent over the same.

2. The system has the standby light on but does not come out of standby.

3. The volume dial makes a scratching sound when turned. Looks like something is out of alignment.

So last 2 weeks were spent reading all Beomaster 8000 related messages to prep for the project. Rudy's (Belover) detailed blog was really helpful to get started.

I will also do a complete recap while trying to fix the above issues.

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dahiyas
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So I started with the Power Supply PCB (6) and followed the instructions from - https://beolover.blogspot.com/2015/02/beomaster-8000-rebuilding-output-stages.html . Sure enough 6c35 was at 1.8nf. Replaced the voltage regulator also. Measured 4.9v on output. So that looked good but the system still did not come out of standby.

Two observations -

1. Anytime I disconnect the main power, I can hear relays clicking (off I assume). Good sign ?

2, At one point while measuring power across 6c35, the system suddenly came alive for a second..with relays clicking and display panel lights coming on. And then silent again...Checked all the fuses, just in case something blew but all fuses were fine. Not sure if anything else blew.  (Yes, I have the Dim Bulb Tester on my to do list..I will complete that before switching on the system again).

Completed recap of Power Supply / Display / Microcomputer / Output Right. ESR meter showed 4 capacitors as damaged and majority of the capacitors were out of the tolerance values. There were couple which showed 5-6 times the original value.

After completing the right side, I moved to the left. 

I started with the filter and tone control pcb. Removed the PCB and first step was to replace the missing buttons that Martin had provided. When I removed the PCB which the buttons press on, I found my three missing buttons - they had come out of their slots and were stuck between the PCB and front panel). The reason they had come out was because the PCB itself had curved. So the three buttons in the middle came out. (I have seen Beomaster 8000 for parts and also panels on ebay that have those buttons missing and used to think the seller tried to fix and failed and lost the buttons - This misconception is now fixed).

So the question is how do I fix the curve ? Without this the buttons wont work and will disappear again. 

Next I started with the Preamplifier PCB. I found two capacitors (C115/C215 - orange) whose value does not match with the manual. As per the manual they should be 10uf/63v but on the board they are 10uf/25v. I don't think the system has been repaired. Which one should I replace with ?

 

I also noticed that some kind of lubricant has leaked from the damping system. (or someone tried to add it from the top or side). It is all over the left side. It's on the output pcb 5. 

Notice the dust on the red connector on bottom right, there is no dust on the resistors below the damping system.(top right). It's all wet and shiny. Could this be the reason that system is not coming out of standby ? Fault-protection mode is activated ?

Any suggestions on cleanup process ?

I will be working on this board later this week.

Dillen
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Dillen replied on Tue, Oct 13 2020 6:30 AM

1. Normal.

Replace connectors on CPU and display modules.
Redo the vias on the CPU board that Beolover also talks about.

Martin

dahiyas
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Thanks Martin.

I will check the cpu board again.

I will come back to the connectors after the recap. 

Any guidance on the mismatch in capacitor values for 3C115 and 3C215 - 10uf 25v(on PCB) Vs 10uf 63v(manual) ?

Again, thank you for your guidance.

Dillen
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Dillen replied on Tue, Oct 13 2020 3:08 PM

dahiyas:

Any guidance on the mismatch in capacitor values for 3C115 and 3C215 - 10uf 25v(on PCB) Vs 10uf 63v(manual) ?

10uF 25V sounds best of the two. Perhaps one was replaced at some point.
Replace with tantals 10uF 25V or 10uF 35V.

Martin

dahiyas
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Thanks Martin.

btw - So far I had just read about the incorrect polarity markings on the PCB's, This is the first time I have encountered them. Lot's of them. I have started marking polarity with a marker before pulling out the old caps.

dahiyas
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dahiyas replied on Sun, Oct 18 2020 11:46 PM

So I completed the recap on all the boards this weekend.

Followed all of beolover's guidelines for different boards and Martin's advice regarding connectors. Cleaned (and Dexoit-ed) all connectors, reflowed solder. I still need to order new connectors. Checked all cables for continuity.

Nothing exciting except I had one capacitors polarity reversed (fixed) and I have the filter store button and balance button swapped (will swap later).

I didn't have the trimmers. Ordered last week and should show up on Monday. so next weekend will be used to replace those.

Some progress.

Good news is that the system now comes alive when input source is selected. Also, some segments on the source display are dead but others seem to be ok so not too bad I guess.

New challenge - The keys stop responding after a minute or so. see picture with vol 2 and fm freq indicator at 10. After this I have to pull out power and connect again and keys start responding again but again for sometime only. Haven't connected external source/speakers as yet.

Any guidance on what to look for ?

Thanks !!

 

 

burbigo3
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burbigo3 replied on Mon, Oct 19 2020 11:51 AM

I really want to help but that seems kinda complicated I should say. Really sorry.

dahiyas
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Couldn't stay away from the project Smile

I pulled out the MP/Display board. Reseated all the cables again. Switched on and the system has been on for about 2 hrs. Keys are still responsive. Looks like loose connections but still doesn't explain the hang after couple of seconds.

So I was brave and connected external input and my headphones..and I heard music. so that's good news.

I found couple of new issues -

1. When I increase/decrease the volume, there is a clicking sound coming through with the audio..is that normal ?

2. The frequency tuning dial is not working. Turning it does not change the fm frequency. Could be the rotary sensors issue ? 

3. The display with the red covers (Clipping/Filters and Manual/Mono) indicators do not light up. I assume bad bulbs (6v/80mA) ?

Any inputs will be highly appreciated.

Meanwhile, I have started my search for right header pins/cables. Any recommendations ?

Thank you !!

 

 

dahiyas
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Issue 1 - looks like I need to adjust the volume control DC offset trimmers (https://beolover.blogspot.com/2018/09/canada-beomaster-8000-filter-tone.html#:~:text=There%20is%20an%20adjustment%20procedure,changing%20(up%20or%20down)

I will swap the filter/balance buttons also when I am doing this.

dahiyas
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dahiyas replied on Sat, Nov 21 2020 11:23 PM

Finally got some time to restart the project.

Source display is restored (finally). Replacing the SMD LEDs requires a lot of patience. Ended up buying a cheap digital microscope and that really helped the process. I am not going to touch the other displays right now and come back to them at a later date. 

dahiyas
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dahiyas replied on Sat, Nov 21 2020 11:36 PM

I changed the trimmers on the output boards and the tone control board.

Adjusted the offset output to 0V across speaker outputs.

Two issues -

1. I am not able to adjust the no-load current. The reading across R236/R237 always shows 0, adjusting R226 has no impact on the reading.

2. The "Offset Volume Control" instructions require a oscilloscope and I don't have one. Can I do this without a scope ? 

Any suggestions ?

sonavor
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sonavor replied on Sat, Nov 21 2020 11:52 PM

You can't proceed without setting the no-load current.
Make sure you are measuring DC voltage across the emitters and not AC.
Check the +-55 VDC rail voltages.
Check the +15 VDC to the output amplifier board.

If the output amplifiers are not set then you don't want to try the volume control adjustment.

-sonavor

dahiyas
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Thanks Sonavor..

56.9VDC and 14.96VDC..so voltages were good.

Closer inspection of the connectors revealed the issue. Connector p54 was not inserted properly. The plug was off by 1 pin and pin 1 was not connected. reseated the plug properly.

No load current was showing -5.6mV. Started adjusting the trimmer (slowly) and the reading kept jumping between the -5.6mV to 18mV. The number kept on fluctuating.

And then there was smell of overheating and a bit of smoke from the heat sink area. I quickly switched off the system. I say bit because I have seen smoke when adjusting the idle current on a penta..it was sound and smoke..here it was very less smoke only / no sound Smile.

So not sure how much damage is done. Since there was smoke I am assuming something was damaged.

I didn't have my dim-bulb tester connected. Not sure if that would have helped ?

Need advice on next steps -

Turn trimmer back to middle, switch on and try to adjust the idle current again ? Hope against hope that the transistors survived somehow.

OR

Do can I do some initial checks without pulling out the heat sink and transistors ?

 

 

 

 

sonavor
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I have never had that happen. There should never be any smoke of course.
The reading of the emitter voltage should not jump like that. It should just gradually increase. 
Were the output amplifier assemblies working prior to the recap work? 
If you don't know or if they weren't working then there could have already been failed transistors so that is what you are seeing now.

You will need to test each of the transistors on the heatsinks.
That can be a bit of a pain to do with everything tight inside the Beomaster 8000 but it can be done. 
Desolder the transistor leads from the output amplifier board and measure the transistors using the desoldered wires.  

I know it is easier to try to recap the output amplifiers in place but I prefer completely removing the assembly and work on them (and test them) individually.
Here is where I removed them.
Here is where I rebuilt them.
Here is where I pretest them.

Please note those are just my preference. There are other techniques people have. I just find it a pain to work on the output amplifiers inside the Beomaster 8000 so I prefer having them out...and while they are out I want to know they are good before reinstalling them.
In any case there is a little bit of pain as removing and reinstalling them has a bit of a learning curve.
Just don't force anything!

-sonavor

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