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
Finally there are some additional modifications (2 additional resistors) to the tone control board. Notice the cut trace near R145. Could this be a factory modification perhaps?
Not sure what to make of all of this. I'm ok with the filter RCAs bypass but wondering if I should bring back the other modifications to factory state. What do you guys think?
Moment of truth: I connected all the boards and cables and ran a quick power up test using a dim bulb light tester and got some 'interesting' results.
First using a 75W bulb, the standby dot would come on. Pressing 'PH', "TP1" or 'TP2' would not do anything. Using one of the FM preset buttons the display illuminated after a delay of a few seconds, relays clicked once but then the unit would shut down immediately. The bulb was very dim btw, no bright flashes.
Having read about dim bulb tester issues with the BM8000, I tried a 150W bulb. Now the unit would stay on with display illuminated but I measured 0mV on the output board resistors. Also, only the FM preset buttons were working, not the other buttons or volume rotary dial.
Next I started to check if the voltages on the PSU board were ok. But wile doing so, all of a sudden the amplifier switched on by itself... I could not activate standby (standby button did not react) so I switched the device off and tried again. The same thing happened: the Beomaster switched on by itself. But now after a couple of seconds the dim bulb tester flashed brightly for a split second before the Beomaster switched off instantly (relays clicking).
Not sure what to make of this. At first I thought it could be a problem with the processor but could this lead to a current surge (dim bulb tester flashing brightly? Any advice or tips on how to proceed would be very much appreciated.
I disconnected all connectors from the power supply board except the ones providing power from the transformers and the starting up circuit board.
When switching on AC via the dim bulb tester, there's an initial bright flash and I can hear the power relays clicking. After the initial flash, the bulb glows normally. Wondering whether the initial peak current is normal behavior.
Also, I thought the relays are controlled by the microcomputer. Not sure why would the relays engage with the uProcessor board disconnected...
I hate that bulb testing fashion. Never used it with hi-fi devices. Useless. Just plug the damn thing.
Jacques
krais: Also, I thought the relays are controlled by the microcomputer. Not sure why would the relays engage with the uProcessor board disconnected...
If I read the circuit diagram correctly then yes, this is normal. The uController can only switch the relay off by setting that output to high, but the relay is actually switched on with the -15V power supply (via R39 and TR18 in diagram 4).
And yes, also the initial flash you see on your dim bulb tester is normal. It's the transformer inrush current doing this. I've never used a dim bulb tester either, but I guess it may be helpful for avoiding blown fuses.
Thanks guys!
Yeah, I spotted the annotation in the service manual regarding the relay circuit the other day. So the relays appear to be working ok and I measured a stable 5.002V on the power supply 5V line.
This leads me to believe there's an issue with the uProcessor board. I'm planning to replace the 2 MHz crystals (https://beolover.blogspot.com/2018/11/beomaster-8000-new-uprocessor-crystals.html) and reflow the vias to see if that will help.
krais: This leads me to believe there's an issue with the uProcessor board. I'm planning to replace the 2 MHz crystals (https://beolover.blogspot.com/2018/11/beomaster-8000-new-uprocessor-crystals.html) and reflow the vias to see if that will help.
Early on in this thread you said you're not a professional in electronics and now you want to re-reflow the board? You're certainly ambitious, but the first thought that came to mind was: wild goose chase.
Wouldn't it make sense to first check with the creator of that post in your link whether his modification actually worked? (I kind of doubt it, but if it did it was sheer luck and there's no guarantee it will work for you.)
In my opinion it would make a lot more sense for you to start testing your boards systematically and try to narrow down the source of the problem!! And you should do that by actually testing and measuring the boards and not by guessing and hoping.In your post after first power-on you said that the trafo relay switched off after a while. There could be several reasons for that, not only the uProcessor board.
If you want me to give you some ideas about the test methodology, let me know. But if you do some reflowing first (which BTW nobody normally does on a through-hole board!!), your system may be in a completely undefined state and then it may be impossible to track down the actual problem!
rgds, manfy
------------------------------------------------[edit]: Just to show you that I'm not alone with this opinion...
Dillen:But - I really would recommend diagnosing and repairing before making any "updates" and "improvements".The initial problem may not be capacitor or trimmer related (indeed I don't think it is in this case) - and by doing a lot of work there's a huge risk ofintroducing more faults, - including faults that have no "natural" cause, - and that could make diagnosing very difficult. THEN - do one module at a time. Adjustments and all.
THEN - do one module at a time. Adjustments and all.
This was Martin's first reply - and he is a professional with hands-on experience in B&O equipment! It's very good advice.
First of all, I really appreciate the feedback. I'll be the first to admit I'm a little out of my comfort zone here...
Here's my thinking and assumptions (feel free to point out any illogical conclusions): When I tried to power up the BM8000 I noticed a number of problems:
#1: My understanding is that common causes are either 5V supply problems on the power supply board or bad vias, solder joints on the uProcessor board. Since it seems that the 5V supply is ok, it seemed to make sense to check the uProcessor board.
#2, #3 could be because of multiple reasons. It just might be the dim bulb tester interfering with the power up procedure. Or there may be other problems which would cause the BM to automatically disengage.
I figured it would make sense to check the uProcessor board first (since it would hard to measure anything with the erratic behavior), then try to power up without the dim bulb tester. Then in case of the BM is still going in protect mode, I could disconnect the boards and reconnect one by one to start narrowing down the cause.
I there another methodology you would recommend?
"But if you do some reflowing first (which BTW nobody normally does on a through-hole board!!), your system may be in a completely undefined state and then it may be impossible to track down the actual problem!"
All true, but the BM8000 processor board is known to develop problems in exactly the through-board connections, causing many kinds of erratic operation, including, but not limited to, intermittent volume or balance changes, Filters in/out and sudden shut-down of the amplifier power.
Luckily there are not that many vias on the board, so it's not that huge a task and, occasionally, reflowing the vias can turn an intermittent fault intoa permanent, which could actually make fault finding easier.
B&O issued a tech note about this with a note to the effect of adding a handful of leads bridging trouble-prone vias.
Others have experienced problems with the crystals. I must say, that I have had many BM8000s on the bench and never had to replace a crystal,- but I have reflowed many of the troublesome vias on processor boards.
Martin
Thanks, Martin! That's good to know.
But here I have to ask: What do you mean by "reflow"? When I hear that term, I'm thinking of a professional reflow oven that allows you to run a specific temperature profile in order to melt and resolder all solder joints on that board. I doubt that any hobby engineer has that type of equipment at home and even if, I fear it can do more harm than good if this person is not experienced in dealing with that process.
Looking at the assembly drawing in the service manual, I'd assume that this microprocessor board is just a simple double-sided board and not a multilayer PCB, and if so, wouldn't it be much easier and safer to simply re-solder those 10+ vias by hand with a normal soldering iron? Or maybe use some jumper wire and solder it on the top and bottom pad - in that way you don't have to worry about micro-cracks in the via-plating or wetting problems in case of improper soldering temperatures.
By reflow I simply mean heat the solder joints up using a normal soldering iron and add a little fresh solder, if only for the flux, to make joints flow and "heal" again.Yes, the board is double-sided with fairly few vias, but the board material and changing temperature plays a role in that theconnection breaks inside the via. Reflowing may not be a lasting solution and jumper wires is what B&O recommended in the tech note.I seem to remember some boards that can't be reflowed, because there really aren't any solder pads at the vias, but merely a small hole.
Not unlike the Beogram CD X, where vias are actual metal rivets that has been riveted and then filled with solder. They develop cracks andbecomes intermittent, not around the rivet heads as one might expect but somewhere down through the hole.The rivets provide ground potential from one side of the board to their respective circuits on the other side and, particularly in combinations, they cancause the strangest faults.The best (and sometimes only lasting) cure here is to suck out all old solder, feed a lead through the hole in the rivet (they are fairly large sono problem) and solder the lead to tracks on both sides.The same board principle can be found in some early 1980s car stereos - knowing that temperature changes has influence imagine theproblems they can cause here,
I can confirm first hand what Martin said.
Last year I was able to get several troublesome Beomaster 8000 Microcomputer boards functioning again. They had various failures similar to what you described. These type of things often cause owners to think the microcomputer ICs have failed. I don't think I have encountered a failed BM8000 microcomputer IC yet. The problems have always ended up being the board itself - solder joints and vias per Martin's description.I am also starting to think a good restoration step on these (Microcomputer boards and maybe other BM8000 boards) is to look at replacing the actual board connectors. I have seen where other restorers have done that. I did that on one BM8000 Microcomputer board but just on the connectors between it and the Display board. One of those connectors was the final piece to getting one of my Microcomputer boards back to full functionality.
Initially I was also puzzled why several BM8000 Microcomputer boards of the same BM8000 type had jumper wires and others did not. Martin's information about the technical recommendation from B&O clarifies that. By now (2020) even boards that had some of that work have other connection problems so really the best solution is to carefully go over everything on those boards. I like Martin's suggestion of reworking the board vias with connecting wire to ensure layer to layer connection.
In the end I have always been able to finally get a BM8000 Microcomputer board working again so be patient.
-sonavor
Dillen: By reflow I simply mean heat the solder joints up using a normal soldering iron and add a little fresh solder, if only for the flux, to make joints flow and "heal" again.
By reflow I simply mean heat the solder joints up using a normal soldering iron and add a little fresh solder, if only for the flux, to make joints flow and "heal" again.
Thanks, now it's clear. It was just a language-specific misunderstanding. I'd just call that "re-soldering of the vias".Yes, that process is fine! However, simply re-heating the solder joint and adding new solder may be a tricky process for somebody with limited experience in soldering. You can't really see the inside of the via. If your soldering temperature is too low, you might not fully melt the solder in the via, if it is too high or if the heat application is too long, the pad & track might lift off the board.
If this were my BM8000 and if I planned to keep the unit for another 10+ years, I'd do following:*) I'd remove all old solder from the vias with a good desoldering pump or high quality desoldering wick.*) clean those vias with a Q-tip and IPA (to remove old flux)*) I'd push a jumper wire through the via and solder it to the board on both sides with fresh solder.*) clean off new flux from those joints with IPA
No thermal expansion or vibration will ever brake that connection from top to bottom layer again. This may be a tedious job, but it would be worth it for me, just for the peace of mind.
I would definitely not replace the IC sockets, unless there are some defects visible on the sockets or solder joints.I also wouldn't touch the crystals or the 1nF capacitors on the +5V pins for now.
I'm not sure if I would replace the connectors automatically, it might be hard to get the right parts. It's true that connectors can be a troublesome source of intermittend problems (cold solder joints, oxidation on the pins, oxidation or bad crimping on the female contacts). But if I didn't see any visual hint of a problem there, I'd probably test the boards before starting to mess with the connectors.
This weekend I disassembled the microcomputer board to reflow the vias and replace the crystals. Here's the board with the shield desoldered. Btw I think someone else already had disassembled the shield, the shield itself was pretty badly warped and some of the solder pads for attaching the shield (this is the mk1 board) were missing.
Here's the board after replacing the crystals (with new 18pf capacitors) and 2 capacitors replaced.
I desoldered the vias and applied some fresh solder. On this board there are wires connecting the 2 sides, so I'm not sure if these older boards have the same common faults. I did notice some suspect solder joints that I reflowed as well and cleaned up a lot of flux residue.
Today it was time to assemble the Beomaster and do a power up test without the dim bulb tester. First I checked the voltages on the power supply board, the 5V, +15V and -15V lines measured all fine.
When connecting to AC, I noticed the standby red dot. The BM did not show the erratic switching behaviour like before so that was an encouraging sign. Finally I dared to tap the TP1 key and well... success! The Beomaster switched on (relays clicked) and did not automatically shut down anymore. All keyboard buttons and the volume dial were now working. The microcomputer self test (pressing 0 + Monitor) was also successful.
I measured around 13mv on the output board resistors so still need to finetune the no-load current and DC offset.
The only issue I found was that when putting the BM in standby and pressing TP1 again, in some cases the relays did not engage even though the display was on. Any ideas on what could be a possible cause for this?
krais: The only issue I found was that when putting the BM in standby and pressing TP1 again, in some cases the relays did not engage even though the display was on. Any ideas on what could be a possible cause for this?
You need to wait until the supplies are bled down before you can power up again.A 20-30 second wait is not unusual.You will also notice the S-meter splashing around a bit as the voltages are going down.
From service note:
Starting problems When re-starting shortly after switch-off (St.by) without load on the output, no mains voltage can be connected to the output. The reason is that the protecting circuit is triggered by a DC shift on the output during switch off. The protection circuit is not reset unil +/- 15V drops to 0V. Until then the RL1 and 2 cannot be activated (15 - 60 seconds after switch-off). The problem is solved by raising the trigger level of the protection circuit adequately to avoid that the DC shift on the output triggers the protection circuit. This may be obtained by changing 5R254 from 120 kOhm ro 390 kOhm.
Starting problems
When re-starting shortly after switch-off (St.by) without load on the output, no mains voltage can be connected to the output.
The reason is that the protecting circuit is triggered by a DC shift on the output during switch off. The
protection circuit is not reset unil +/- 15V drops to 0V. Until then the RL1 and 2 cannot be activated (15 - 60
seconds after switch-off).
The problem is solved by raising the trigger level of the protection circuit adequately to avoid that the DC shift
on the output triggers the protection circuit.
This may be obtained by changing 5R254 from 120 kOhm ro 390 kOhm.
Dillen:You need to wait until the supplies are bled down before you can power up again.A 20-30 second wait is not unusual.
Thanks Martin! I guess this means that the microcomputer is working fine. I also checked the remote and that works without issues.
Now for the bad news...
I did a quick test hooking up an audio signal to tape 1 input RCAs to see if there would be any sound from the headphone output... nothing. When I checked the connectors on the preamp and tone control boards I noticed that a ground pin on P27 on PC4 had come loose. After reinserting that pin firmly in the connector housing and switching on the BM all of a sudden... magic smoke.
Not a big bang, just a puff of smoke around the starting up circuit board. I've narrowed it to the left bridge rectifier (one of the internal diodes has shorted).
Wondering if this is likely to be a normal part failure or could there be an underlying cause that I need to investigate? Any advice on a replacement part (or specs)? Thanks!
At first, congratulations to your success with the uProcessor board.
krais:Not a big bang, just a puff of smoke around the starting up circuit board. I've narrowed it to the left bridge rectifier (one of the internal diodes has shorted). Wondering if this is likely to be a normal part failure or could there be an underlying cause that I need to investigate? Any advice on a replacement part (or specs)? Thanks!
Smoke coming from electronics is never really a good thing! There must be a reason for it and that GND connection you re-attached to PC4 is the first thing I'd look at.Without disconnecting any wires from the board I'd check all the supply rails that were served by that rectifier. Check if there's any short circuit with a multimeter.
Which rectifier blew up? 30D1 or 30D2?The service manual shows "KB 62-B125/110-25" for both rectifiers but I couldn't find any datasheet on the net. Check the component marking on those bridge rectifiers. It will help to find a replacement.
PS: After some more googling it shows me a Diotec bridge rectifier 400V/25A, square metal case with 6.35mm connectors. If that's the one installed, then overcurrent is unlikely - that current would have blown the fuse and/or some other components on its way to heaven. That supports your random component failure idea. Nevertheless, I'd also do the short circuit checks described above just for peace of mind.
Thanks Manfy
manfy:Smoke coming from electronics is never really a good thing! There must be a reason for it and that GND connection you re-attached to PC4
Sorry I wasn't clear, I think this is a signal ground pin (P27-3).
manfy:Which rectifier blew up? 30D1 or 30D2?
The left rectifier when looking from the front of the BM, so 30D1
I just edited my previous post; please check.
The circuit diagram shows that 30D1 only supplies the +/-55V to the left output amplifier. Random component failure is possible, but I'd still check very carefully for any potential short circuit that could have caused this to the rectifier.
If you're certain that everything is fine you should replace the rectifier and verify the power supply voltages with all other boards disconnected before starting to reconnect the boards and testing further.
Apologies Manfy for wasting your time, I may have jumped to a wrong conclusion earlier. Did some more measuring out of circuit and the bridge rectifier seems intact after all (0.48V one way voltage drop across the diodes).
It's all rather confusing. I'm quite sure I saw smoke on the left side of the power up circuit board but there are hardly any components on that side of the board. The 2 fuses haven't blown and resistors R1 and R2 are within spec (5.6 ohm).
krais: It's all rather confusing. I'm quite sure I saw smoke on the left side of the power up circuit board but there are hardly any components on that side of the board. The 2 fuses haven't blown and resistors R1 and R2 are within spec (5.6 ohm).
Hi,
If you think you saw some smoke then you probably did. Something could be shorted somewhere and resulted in too much current through a component. There are two power relays on the component side of that BM8000 Start Up PCB. You can open that Start Up board some more so you can watch what happens on the next power up attempt.Before that though, re-check all of the BM8000 wires. Because you rebuilt the output amplifiers and tested them already they should be good. Did you make sure the black ground wires are attached on the backside of the Microcomputer board?
P27-3 is a ground connection between the Filter Control panel and the Preamp board. If connecting it completed a connection that exposed a problem in the Beomaster then it could involve 15 VDC power. How that affects the Start Up circuit I can't guess right now. 7RL1 and 7RL2 must both engage to apply the ±55 VDC rail voltages. The rails must also have +15 VDC for the output amplifiers to turn on. I am not seeing the ground - Start Up circuit - smoke correlation but I believe there is some indirect thing going on there. If you don't find any wiring issues I would try the variac and dim bulb tester again as a precaution. I recently blew out a couple of TIP 146 transistors on a Beomaster 4400 because I didn't trust my dim bulb tester. Voltage was applied and measured fine at first but then started to drop. I took the dim bulb out of the power path and the two good Darlingtons were gone. I should have seen the dropping voltage as a sign that there was something wrong.
Smoke is another sign :-). Hopefully it wasn't fatal for some poor component. Check power on the BM8000 with the dim bulb protection and re-check what voltages come on (both in Standby and with an audio source selected). With something like Tape 1 or 2 selected all of the power should come on and you should here the relays click on the Start Up board. Check the +5 VDC regulator and the ±15 VDC regulators next to it.
One other thing...Double-check the Power Supply Board (PCB6) that 6P50 and 6P51 connectors are correct. Those two connectors have the same physical keying so they could accidentally get swapped. They also both play a role in the Start Up circuit.
Thanks for the help Sonavor!
I'll do some more thorough checking/testing this weekend, making sure to use the dim bulb tester for the voltage checks (I don't have a variac at this time).
One other theory that came to mind: maybe the smoke was not coming from the startup circuit board but from the tone control board instead. The smoke could have been funneled upward between the pcb and the control panel and exited near the reservoir caps (making it look like it was coming from the startup circuit board).
I'll do a visual inspection of PC4 first before starting with the voltage checks.
Okay. A variac would be a great addition to your tools. I use the variac more than my dim bulb tester. My tester is designed to monitor the current and voltage with the variac as I apply power to the unit under test. The dim bulb portion of the test can be switched in or out of the path since I only use it when I am powering up an unit for the first time.
If the fault was on the tone control board then did you hear the two relays (7RL1 and 7RL2) engage when you tried to turn the Beomaster on?
sonavor:If the fault was on the tone control board then did you hear the two relays (7RL1 and 7RL2) engage when you tried to turn the Beomaster on?
The relays engaged when turning the Beomaster on but immediately the magic smoke appeared. Can't remember if the relays disengaged but the display stayed on.
Okay, well when you fixed the wire in the connector that allowed a missing ground to make its connection on the Tone & Filter board so it sounds like there is just some problem localized on that board. Hopefully that will be easy to diagnose and fix.
I took a closer look at the left side of PC7 and did find a very dry solder joint on the AC trace (no burn marks, still continuity). Could that have produced enough heat to cause a small amount of smoke? It cannot possibly be that easy, right?
What device does that lead go to? That is the type of thing you need to look for when going over this Beomaster though. Even if it isn't the source of your immediate problem it could become one in the future.
No, I'm afraid not. A cold solder joint cannot create smoke -- unless there is arcing, in which case you'd see burn marks and you could smell a dinstinctive "electrical" smell.
It's more likely that the smoke came from R1 and R2 because of heating up rapidly, but that would imply that there was a high current drawn on the output side of the transformer. Those resistors are 5.6 ohms/5W and the trafo fuse is 4A slow-blow. So if the input current was 3A the fuse wouldn't blow but the resistors would have to dissipate good 50W. Now, that can cause smoke.Normally, relay RL1 would switch off those "soft start" resistors after 1 or 2 seconds and such a short overload shouldn't create smoke - heat yes, but not smoke.
Just re-solder that solder joint and since you're at it, check that RL1 makes proper contact. It should be well below 1 ohm when the contact is closed.Relays do have a limited lifetime and if those contacts have deteriorated, this inrush current limiter is not completely switched off in normal operation.
[cross-posted]
manfy:Normally, relay RL1 would switch off those "soft start" resistors after 1 or 2 seconds and such a short overload shouldn't create smoke - heat yes, but not smoke.
Hmm I assumed that the interval between the two relays engaging would be much shorter. So what I thought was a double click was probably just RL2 engaging all along, not RL1. I'll investigate RL1 to see if that component is working and makes proper contact. When testing the relay out of circuit what voltage should I apply to switch on?
Also, what I noticed is that if the Beomaster is turned on, switching to standby will cause a relay click, but when subsequently unplugging from AC there is another relay click. Assuming that a relay cannot switch off twice, would this also indicate a problem?
There should be apprx. 1/4 of a second between the two relays activating.
Close to a “double click”.
I agree with Martin.
I don't have hands-on experience with the BM8000, but all the other high-end high-power amplifiers I've seen have a distinct double-click (usually in a 1 second range).
Looking at the circuit diagram I see that RL1, which disables the inrush current limiter, is driven by 40VAC via D21. So that's a half-way rectifier with an output voltage of approx. 18VDC. But you can check the printing on the relay; it almost always shows the nominal voltage there.
After the diode there's the RC circuit R27 + C20 and I calculated an RC time constant of 0.63sec. Without analyzing the switch-on circuitry with TR21 and TR22 in detail, I'd say that TR22 would probably switch the relay on after 0.5 to 1sec. At power-off RL1 should open immediately because the smoothing cap C21 with 22uF shouldn't be able to supply the relay current for more than a few line cycles, i.e. 100msec maybe.
The main relay RL2 is controlled by the uProcessor and it switches on the power trafo that supplis the output amps and this RL1 circuitry. I didn't see any other relay in the diagram - but to be honest, I didn't scan every little bit of it!
If there are really only these 2 relays in the BM8000 then it would be very strange to hear another relay click after putting the unit into standby (aside from RL1 and RL2, which should switch off simultaneously when the uP signals standby)!!
-----------------------------------
Oops! I may have to take my last statement back!
I just noticed that the main relay RL2 is driven by -24V from the standby transformer. So, this voltage is available as long as the unit is plugged in.RL2 is switched off by a High signal from the uP. So if this signal drops to 0V, which should happen immediately after unplugging, there might be time before the -24V decay to 0V. In this case the relay RL2 may switch on for a short moment (until the relay current bled this -24V supply to below holding current. This would probably happen in an instant and it may sound like a single click.)
This scenario is thinkable but it needs to be confirmed by insiders! Hmm, on second thought, I see that the standby signal is also swithing that supply circuitry via TR5!?? I'm not sure. Let's wait for Martin or other guys with BM8000 experience.
There should be no click when mains is connected.When mains is disconnected while the Beomaster is in standby it's not unusual to hear a relay click on/off.Perhaps because the supply to the processor falls down faster than the supply to the relay driver etc. and a low signal from the processor is then "interpreted".I never dug any deeper into this.
krais: Also, what I noticed is that if the Beomaster is turned on, switching to standby will cause a relay click, but when subsequently unplugging from AC there is another relay click. Assuming that a relay cannot switch off twice, would this also indicate a problem?
When the Beomaster 8000 is in Standby and you press a music source you will hear two relays click on very close together like a "tick-tock". Pressing Standby when a music source is selected will dis-engage both relays but they will almost be in unison. So it won't be "tick-tock" but you can still hear two relays. Unplugging the Beomaster 8000 when it is in Standby will result in the relays cycling. It will be the "tick-tock" sound.
Hi
Maybe you have a closer Look to the big AC Mains Capacitator wich is located on the Relay PCB.
My BM 8000 was playing music, suddenly I heard a crackling and sparkling Noise of the Amp with a lot of bad smelling Snoke comming out of Direction of the Right Amp Board...but the BM was still playing Music and after shutting down and opening the BM I could´nt realy find anything burned.
Checked some Voltages, No Load Current and Offset, everything fine.
So I put back to AC and starteted the BM and he was still working proper.
Final Investigations sortet out that the AC Mains Cap was totaly kind of "exploded"
Mounted a new one and everything is fine aggain.
Best Regards
Christian
Spassmaker:Maybe you have a closer Look to the big AC Mains Capacitator wich is located on the Relay PCB.
Thanks Christian, I already had proactively replaced the Rifa safety cap as these are infamous for catastrophic failures due to old age.
Update: I figured out why RL1 would not engage. Another loose connector pin, this time P51-3 on the power supply board that controls the relay.
So this would have caused a continuous current through R1, R2 potentially causing the smoke to appear. But as that happened immediately after switching on the Beomaster, in this scenario there could still a fault somewhere that is causing a high current to flow through the resistors as Manfy indicated.
So some more troubleshooting left to do...
With your Beomaster 8000's recent history of connector problems I would check every connector again. ;-)