ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
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.
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.
1. Normal.
Replace connectors on CPU and display modules.Redo the vias on the CPU board that Beolover also talks about.
Martin
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.
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.
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.
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 !!
Couldn't stay away from the project
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 !!
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.
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.
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 ?
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
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 .
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 ?
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
dahiyas: 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.
I miss-posted earlier about the no-load current measurement and may have thrown you off.What I meant to say was that on your DMM, make sure you are measuring DC voltage across the emitter resistors for the adjustment and not AC voltage.My meter likes to default first to AC and I have to switch it to DC.
Sorry for the bad information.-sonavor
No problem.
I bought this used and the only thing working when I started was the standby light. After the recap I had plugged in headphones and that worked fine. (except the clicking on volume change - volume offset needs adjustment).
I have changed the connectors on the cpu/display board and that has fixed the intermittent standby/display issues.
I will proceed to checking the transistors.
Don't have the external power supplies but we'll come to that later.
Thanks again for the inputs.
Sonavor - Good news and bad news .
I couldn't resist connecting speakers
Looks like the left output pcb survived (the one I was trying to adjust and saw smoke). I connected penta (minus the amp) and left side plays well.
But the right side is bad. I can hear low volume from the right side with distortion. The volume keeps fading out and coming back.
Either this pcb was bad prior to me getting the system or while I was focused on the left pcb, the right pcb would be heating up if idle current was out of spec and that killed the board. Ideally, should have worked on one board at a time - replace trimmer and adjust, then move to next board.
As indicated by Martin/You in other posts, will rebuild both the boards in any case. The TIP's and other parts are not that expensive.
Are there any equivalents that I can look for if I don't find the TIP141/TIP146?
Well...these things happen.I would look for TIP141 and 146 devices. You should be able to find them.I am a little unclear on the left channel output amplifier board. Were you able to finally adjust the no-load current on that one?
The boards shouldn't require a rebuild if you already worked on them. It sounds like there was a problem with the transistors that finally caught up to the output amplifier...once you replaced the capacitors. -sonavor
Yes, I had replaced all the caps on all the boards.
After finishing the setting of left, I looked at the right side. I noticed that the heat sink was hot. So adjusted the idle current trimmer and also the volume offset . switched off the system and waited for 10 mins. The heat sink was cool again. Switched on the system. The heat sink did not become hot but felt heat from the output pcb. switched off again. Both the BF857s were hot.
Playing source through TP1, produced good sound from left but very low/shrill volume from right with volume fading in and out.
I would leave the left channel output amplifier board alone then.One nice thing about the way it turned out...If you do want to remove the whole output amplifier assembly so it is easier to check and work on, the right channel is pretty easy to remove the way I showed on the blog. The left channel is the tricky one and has to be rotated ninety degrees to remove it out the back.
Remove and check the transistors on the right channel output amplifier assembly as a start.
I did pull out the transistors. All of them read 2.5v-2.8v between B-E instead of OL.
Have ordered replacements. Hopefully will be here by weekend.
What are the other components I should be checking on the output PCB ?
Your measurements of the TIP 141 & 146 Darlington pairs seem a little odd. A good transistor of those type measure with a Vbe of around 1.13V.With a failed board like that one I would check all of the semiconductor components (transistors and diodes) to be safe.If you plan on doing more restorations it is worth it to invest in a good transistor/diode tester.-sonavor
Yes Sonavor...This is my destressing activity..so have been buying tools on need basis.
I did use a DMM to test the transistors and followed the general guidelines for testing a NPN and PNP transistors.
I did pull out my component tester and tested all the transistors. None of them came up as "damaged component".
TIP 141 - hFE - 36/35/35 ,Ube - 996/996/970mV, Ic - 5.6/5.6/5.6mA, CE - 578/570/567mV
TIP 146 - hFE - 27/35/31,Ube - 873/858/862mV, Ic - 5.7/5.7/5.7mA, CE - 587/575/582mV
That's good news then. Your IC201 through IC206 transistors are likely good.The bad news is you will have to keep going and check the rest of the transistors on the board. There are eleven on the PCB itself and one small transistor on the heatsink (TR208).Then there are twelve 1N148 diodes and one 9.1V zener diode.
I looked at the PCB carefully and I think one of the legs of a 200uf capacitor was not soldered properly. (Lesson to others - please listen to the experts who recommend pulling out the PCB for recap.).
Can that explain the volume fading in and out ?
I de-soldered and checked all transistors and diodes. everything checks out ok.
Did the loose capacitor cause the volume and heating issue ? I was able to set the trimmers to the right specs.
Sonavor - Any other checks you can recommend before I put the board back ?
I can't think of any. It sounds like you checked all of the component thoroughly.When you say you set the trimmers do you mean you did connect up power to the output amplifier and do the idle current check?
Yes Sonavor, the trimmer settings were done prior to me pulling out the board and transistors. 18mV and 0mV. After performing the settings, I figured that the right channel was not ok.
Yes, all of the components tested ok on the component tester.
Only thing I can think of is the bad solder joint. I had done the recap without pulling out the boards on a vertical board. Soldered all the caps again also checked the polarity again. But not sure if that would lead to the BF857 heating up so quickly.
I don't have much of a choice but to put the board back. Don't have any external power supplies (as yet) to test the board outside the system.
Will report back once done.
I have a hunch it will work this time.If you do decide to invest in some bench power supplies make sure you get ones with a current limiting feature. On my 60 VDC supplies I preset the current limit so they won't exceed what the Beomaster 8000 Output Amplifier board can take. If something is wrong on the board and it starts demanding too much current when I test it then the power supplies just shut down.-sonavor
Yesss !! It works. Looks like it was the capacitor. So now the sound does not fade in and out. No distortion.
BUT
1. I felt the BF858s were really hot. But Krais also mentions the same and Martin/you confirmed that its normal.
2. I also noticed that D5 on the power PCB is also hot. Is it because of the proximity to the voltage regulators ?
3. I checked the trimmers again. The idle current keeps increasing in small increments after setting to 18mV. Similarly, the offset output keep on going higher. Anyways after getting closest to 18mv and 0V, I tried playing music for 30 secs and I switched off the system.
Any guidance on pt. 3 ?
Looks like our messages crossed !! It did work.
Sonavor...I really appreciate your guidance on the additional equipment. I have quite a few things on my list and projects that can use the items.
But just when I am ready to buy the next item..something else shows up. I was ready to order power supplies (3 x 60V) and a MS150.2 showed up in DC. I ended up buying it (Cost of shipping from DC to ATL is same as the MS150.2 :-()
so power supplies get pushed out ..for now. Have to deal with a upset better-half when the boxes show up !!
Hopefully..the BM8000 can be ready before they show up.
While the Beomaster 8000 is warming up the idle current can drift. It should settle in though. The DC offset should stay withing the service manual tolerances.You are measuring the idle current with the speakers not connected and the volume level at zero right?Monitor it for a while and see that it stays around the 18mv across the emitter resistors.Those BF858 transistors do get up around 160°F. That's why I use 105°C rated capacitors. -sonavor
To be honest I have read about the 105°C rated capacitors but feeling the heat coming from the regulators after just 5-10mins and the BF858s, it makes more sense now.
Played a bit more today and no more heating of heat sink.
New challenge - I just have one speaker connected. BALANCE controls - When moving balance to the right the speaker volume increases and when moving to left the volume on right comes down again till 6 and then cuts off completely at "<".
I would have expected the volume on right to go down gradually when moving balance to left and also volume on right should not be increasing when moving to the right.
Not sure if this is normal behavior on the BM8000 or I have messed up some connectors.
I checked the connections again and they are ok.
Volume Offset adjustment ? I did replace both the trimmers on the tone control board.
Can I do this without a scope ?
I have done it without a scope. If you are in a nice, quiet environment you can hear any clicking through speakers or headphones when adjusting the volume (with no music playing). Adjust the trimmers where there is no clicking sound. If you changed components with that circuit then you might need to start with any removed resistors reinstalled to begin the procedure.
Thanks Sonavor.
What about the balance control - When moving sound balance towards a side..does the volume on that side go up ?
When you say the volume on one side goes up does the Beomaster 8000 volume indicator go up?
So lets say volume level is currently 4.0.
I have only one speaker connected on right.
When I press balance right, (1 > 6), i can definitely hear a volume increase with each press, and so does the balance indicator BUT not the main volume indicator.
Similarly when I am at max ">" on right and I start reducing (press balance left).. there is a audible volume decrease till 0..then as I move towards left 6, the volume does not reduce till 6. It cuts out for right speaker at "<".
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I would have made a video but I have run into new issue now.
After I switch on the system and play music..the displays either switch off completely or partially. The music continues playing. The keyboard becomes unresponsive. unplug the system and plug again and same behavior is repeated.
I have never tested a Beomaster 8000 in that condition. I always have to load resistors or speakers connected.With two speakers connected and music playing the balance control works just as other amps. It removes sound from one channel down to where it is silent. The volume level of the remaining channel doesn't change.
On your new problem it is difficult to diagnose.Have you checked the voltage adjustment on the Display board? Make sure it is set properly and not interfering with stability on the Microcomputer board. Just something to check. -sonavor