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
greetings All 😁
after I finished a total recap job on my MB8000 the time to test that monster finally arrived......😢
the Standby dot showed, turning it on only fired up the display ?
no idle current could be adjusted as there is no power/current present on the output boards ..... ?
checking the start-up circuit I unearthed two dead resistors: R1 and R2, the 5.6 Ohm/5watt types !
as I received the BM as a ‘not working’ unit I can not say anything about its history....all power darlingtons
on the heatsinks were dead with the exception of 2.
while I did the recap job I noticed most boards looked untouched, no obvious signs of previous repair attempts.
the question is: what was the reason for 7R1/2 to fail ?
Both are critical (fuse-like function) and I feel somewhat hesitant to simply replace both to prevent any further damage ?!
as usual, betting my life on a recap job with a warranty is not an option but I took a long time to make sure
silly mistakes to be avoided at all cost 🙄
has anyone had a similar issue with the star-up circuit and if so what was the cause ?
missing segments on the DPs are a minor issue for now ! As always, your comments are appreciated and invited.
ALF
PS: removing the left channel output board only took a lifetime under utmost caution 😡 gaining experience is such an uplifting feeling 🤙💪😁
Ok,
the two fuse resistors 7R1 and 7R2 are replaced but still no starting-up, only a short lighting up on two displays followed by relay clicking and everything is off again.
on to the fault switch (TR 15/16/17) : all transistors tested ok, which tells me the fault switch should be doing what its supposed to do.
now on to finding what could possibly causing the short ??
one suspicion:
some or one of the power darlingtons mounted is making contact with the heatsinks, shifted off the mica foil while being installed ? - don’t you hate that gooey white paste 😬
I also noticed the 330nF capacitor (as per SM) on the starting-up board is infact a 0.1uF cap ?
still hoping for some pointers and ideas as this monster is quite complex....!
thanks
Hi Alf,
It is too difficult without actually seeing what you are doing and really looking at it myself to provide you with anything concrete. However, in this type of scenario you should get down to basics and start simple. Since the fault is resulting in problems with the start up circuit you need to start with power coming on. You have +5 VDC since the standby LED comes on when you plug the Beomaster in. When you press a function to use some audio source is when the main power tries to engage. I suggest removing the power connectors from the boards (output amplifiers, preamp, tuner, filter & tone control) then turning the Beomaster on. If the Beomaster comes on okay like that then it will indicate the problem is power routing to one of the boards and you can one-by-one locate the culprit. If the Beomaster still doesn't come on then you can focus on the power supply and start up circuit side of things.
John
Also....regarding installing the left output amplifier assembly, I was able to capture the sequence on this Beomaster 8000 I am working on. If the transistor spring clips are mounted correctly they shouldn't shift as the board is being manoeuvred into position. It is still not the easiest of installations (or removals) but it is per the service manual and does work.
Hello John,
my apologies for the delayed response......right, sadly I have to agree with what you pointed out....I also knew this would be a very
big challenge the BM8000....I looked at it as a kind of tutorial, loosing fear of opening the monster is nice.
I should have done exactly what you suggested right from the start of trouble.
well, I disconnected power from the 2 output amps (red and black wires) and the 15V supply, similar to the filter/tone control and the preamplifier.
this way I can switch on the BM out of standby ...no trouble.
in the meantime replaced the the 2 fuse-resistors R1 and R2 on the the starting-up board and replaced
the no-load adjustment trimmers on both output amps.
reconnecting the preamp and tone control/filter boards still caused no problems.
on to the first output amp board - next to the power supply: still no problem bringing the BM out of standby, however the no-load current adjustment
is extremely touchy and seem to drift over time, which caused some concern 🙄😡😬 and also checked the board’s two BF type transistors...all good.
that leaves the second output amp - next to the preamp board as the main suspect ?! I could not detect any cracked joints, all BF transistors tested fine....
this is where I stumbled over the first roadblock !
I thoroughly checked the connections of the power darlingtons on the heatsinks.....nothing to see, unless one or two make contact outside the mica insulator...which I could not see.
I scanned an archived post of yours from 2013? to see if there are similar problems that may have occured to your BM8000.....but wasn’t the case.
BTW, those 3 voltage regulators connected to the PSU are all fine at 4.95V, 15V and -14.94V.
apart from replacing the old no-load trimmers I noticed that both wire-wound resistors on the “trouble board” were practically “naked”....due to excessive heat ?? Both were replaced as well.
this is where the projct stands at the moment.....question remains, is that second output amp board really responsible for triggering the fault switch
or is it fair to think of that big second rectifier next to the associatd reservoir caps ??
Which output amp are you calling the first one? The right channel? Is the left channel output amplifier the one you are having issues with? The output amplifiers do connect to the fault circuit. From your description above did you hook up and try the left channel amp again? While your suspected output amplifier is disconnected what do you measure on the diode bridge that supplies its ±55 VDC?
What is the history of the output amplifier board? Did it ever work for you? Does it have a lot of burned areas on the board? Due to the trouble with working on the amplifier board while it is install and the trouble removing/installing it is why I prefer to test my reworked amplifier assemblies outside the Beomaster by themselves. It does require a bigger investment in test equipment but like to know those assemblies are working before reinstalling them.
Hi John,
well, I am aware testing the output amp board outside while not being installed would certainly help but with pensioner budget restraints
there is not a lot of money left for additional testing equipment 😢😬
I did reconnect the “good” output amp again while the trouble side remained unplugged and as said, tried to adjust the no-load current to 18mV....
it is getting there after a while but very touchy to adjust ??
on the “good” side I got about 49VDC at the + terminal of 30D1, same at the +\- terminals of the big reservoir caps.
checking the “trouble” side delivered a jumping array of mV at the + terminal of 30D2, dito at the big reservoir caps........
i will check the diodes of the rectifier.
to clarify: looking from the front of the BM....
the “good” ouput amp is the right one, next to the power supply board.
the “trouble” output amp is the left one, next to the preamp board.
Well of course the faulty amp would have to be the left channel output amp which is the most difficult to remove. I understand about budgeting test equipment. Like woodworking there are ways to get by with less tools but having the right tools make jobs so much easier. I was just saying the reason I do it is because I do quite a lot of them and it saves me a lot of trouble doing it that way. You can still solve this without testing the boards externally. Did you replace the 100Ω trimmer resistors for the no-load current adjustment? What does the +15 VDC look like to the output amplifier boards.
Yes John,
it had to be the difficult one !😬😬 ...... one doesn’t like those cheap quick repairs !
naturally it would be easier to have an external test-facility ..... no intentions though to pull out that board one more time too many !
just checked: 15V is present, both 100 Ohm trimmers for the no-load current adjustment have been replaced.
I wonder if I would have to unsolder the big rectifier as it has connections to the 10K uF reservoirs in order to test safely without getting zapped ??
sadly I do not know anything about the BM history, except I bought it as a non-working unit with most power darlingtons at the heatsinks missing.
two brand new sets have been installed in the meantime.
The BM is in quite good condition otherwise, minus the usual missing segments in the DP’s which is the least of my worries for now.
one of the questions I have : is the big rectifier damaged as I am getting 35 and 39 VAC on its AC terminals ?!? and basically nothing on
its VDC terminals except a few mV ?!?
On the bridge rectifier for the ±55 VDC rails I get around 76 VAC, 60 Hz across the AC power in terminals from the transformer. On the output terminals of the bridge rectifier (which goes to the reservoir capacitors) I get 105 VDC. You should be measuring across your AC terminals and not each terminal to ground independently. So it looks like you have over 70 VAC there. Measure the voltage across the output terminals (DC voltage). It sounds as if the power in is probably good. I would suspect the left channel output amplifier board. It also sounds as if the right channel board also has some problems.
right again John,
I get around 75 VAC across the AC power and 95 VDC going to the big caps !!!
both boards are getting the 15 VDC, both boards are getting decent VDC, both boards are recapped, I checked the BF type transistors which had a slight discoloration around but all fine.....
of course there are other components on the boards #5, but off-board we have the power darlingtons, which should be fully isolated from the heatsink, right?!
I will check some other components of the right board first and then move on to my favorite one
the “difficult” output board is removed again:
another close inspection of possible soldering issues - no findings !
checked every transistor off-board - all tested fine !
Checked all diodes - all testd fine ! no broken resistors either.
I am aware testing components can dliver “OK results” but load conditions may deliver the opposite?!
Next step is reconnecting the board with only having the -/+55V red/black wires connected, leaving disconnected the yellow/white/brown/blue wires incl P37 which only take care of the speaker and phones terminals.
this way I hope to exclude the heatsink mounted power darlingtons as culprits ?!
Yes,
I can turn on the BM having only the -/+55V supply wires connected.
Introducing the yellow and green connectors next.
Correction, no Yellow tab to pull off !
I reintroduced the Green and Blue tab and the BM can still be switched on, however the no-load current adjustment shows no voltage ??
I noticed when the BM is ON and switch-off is activated there is no relais klicking to be heard ?? Odd !
anyhow, after reconnecting P39 to the output board the BM won’t switch on.....same as before.
It is getting interesting......
These are the minimum wires (check the second picture in blog link) that have to be applied for power to the output amplifier boards. You cannot only connect the red (+55V) and black (-55V) wires. You need power ground (blue wire). You also need the connector with +15V.
Yes, that’s correct John 🤗
exactly what I had done at the end, building up to: from the black/red plus blue plus green (no need actually) and plus the 15V supply plug !
As said John ,
that is what I ended up having had connected - things were looking promising, but a couple of odd issues are:
why is there no voltage across those emitter resistors to check/adjust the no-load current ?
why isn’t one of the relais klicking when turn-off is activated ?
why is the connection of P39 causing the fault switch to kick in ?
I am sure the are expanations for it and I am still up-beat to find them.....with a little help ?🙄
Hi,
P39 is the signal ground, which is also used to control the amp: i.e. TR 203 base is connected to P39! via R212 to signal ground. It's collector is connected to the 100R poti which is used for the DC Offset of the Output! This could cause the activation of the protection curcuit cutting in!
The output darlingtons should be mounted with micas to the heatsink.
Ralph-Marcus
RaMaBo: P39 is the signal ground, which is also used to control the amp: i.e. TR 203 base is connected to P39! via R212 to signal ground. It's collector is connected to the 100R poti which is used for the DC Offset of the Output! This could cause the activation of the protection curcuit cutting in!
That reminds me. On one of my Beomaster 8000 restorations I was having problems on the DC Offset adjustment. TR201 and TR202 measured fine with a transistor tester out of circuit but Martin suggested I replace them. The Hfe on one of those transistors was about half of the other. Once I replaced them the DC Offset adjustment was able to be made.
I am not sure if that is your problem because your symptoms really sound more like you have a ground problem with your setup. Make sure the lone P37 pin has its ground wire connected. As Ralph-Marcus pointed out, P39-1 connects signal ground to the board's power ground. When you do that on your problem board the fault circuit is triggering.
Many thanks Ralph-Marcus for your input - very much appreciated 😁
yes, all Darlingtons at the heatsink are sitting on Mica insulators but thanks to that goey paste and the firm sitting metal spring it is possible
that one had been shifted just a tick off that insulator in the process and could make contact with the heatsink ?!
of course the ground connction is important...an oversight of mine 🙄😬
once again thank you
Thanks again John,
same here.....did not pay attention to the hFe readings when testing was done on those transistors in question - both did show indeed
very different hFe readings - will pick up new ones and select - also replaced that old 100 Ohm trimmer pot and shall reconnect again to see what
happens this time
reconnection time tomorrow !
I decided to recheck the hFe level of the two transistors 5TR201/202......indeed they measured quite different.
new BC546 were selected with a very close hFe match for both output boards, as well as a replacement fir the old trimmer pot R200.
see what tomorrow will bring - I shall be back with news.
Hello again,
after replacing the TR201/202 pair - selected with a matching hFe reading - plus new R200 trimmers on both boards for the offset adjustment
it was time to reconnect....🤬
same problem again, the safety switch kicks in and I can not start the BM ! Disconnect the suspect output board and I can turn on the BM !
once the safety switch was activated there is nothing to measure on the suspect board 😬
I dare to say TR201/202 plus the new trimmers can not be the cause plus P39/P37 with its single ground wire were connected at the time.
so, at the moment it looks pretty “dark”.
Yes, it obviously looks like this ouput board is the culprit and not the starting-up circuit ??? Such a pain that I can not test that board separately.
Hi Alf,Testing the output amplifier assembly by itself is very handy for me but it is not the only way to solve the problem.It is very difficult to help when we are completely blind to the problem. You rarely give us any detailed pictures (or any pictures for that matter).My suggestion on the next step is to swap the right channel output amplifier assembly with the left. That will verify that the left channel output amplifier is the problem if the problem follows it (to the right channel). If that is the case then it is also easier to measure and work with the fault on the right side.
yes, point taken....it is very hard to suggest something blind here....however taking poctures is also tricky for me as I can get much better pictures with the iPad than with my old digi camera but they all turn out much too big to upload.... and then the question what to picture ?
sure, I could take detailed shots of the output boards which I am very happy to present but would that really help ?
anyhow, thank you for the suggestion of swapping over the two boards...brlliant idea I thought - I will do so taking with them the attached heatsink assembly.
I still find it a lot less stressful to unsolder the heatsinks and unplug the wire tabs from the board 5 before removing them...any other “trick” is too dangerous ripping off some wires without noticing ?!
back to work, I shall report back - if you can suggest any specific pics I will try my very best to provide....
talk later
I finally got around to swap over the output boards with their heatsink-mounted power darlingtons.
it looks very much like the board in question is indeed the problem as John pointed out right from the start.
Because the fault switch kicks in straight away I can not actually measure any voltages on that board.....! So, I presume
it is taking off components like all diodes and testing again......plus there are the off board mounted darlingtons.....
anyhow, something is triggering the fault switch...😳🤬...??
another question is: is the fault switch activated or is it the current limiting circuit ?
Another thing to check. Don't connect up your dim bulb tester for these tests. It will interfere with the power and fault circuit.
Hello SB,
many thanks for coming on board......very much appreciated 🤗
a quick recap of events:
1. BM arrived as a ‘non working’ unit, most output darlingtons from the heatsinks were missing
2. A total recap of the whole BM was done, including the installation of two new sets of output darlingtons.
3. The two high wattage 5.6 Ohm resistors on the starting-up board were replaced - originals been way out of spec.
4. The no-load current adjustment trimmers plus the 2 emitter-resistors (0.18ohm) on the suspect output board were replaced.
5. No-load current adjustment on the “good” output board was possible but very touchy.
6. A switch-on test uncovered the “suspect output board” and triggering of either fault switch or/and current limitter circuit ?!
6. All transistors from suspect-board #5 were tested off-board
7. TR201/202 were replaced - thanks to a recom by John - with a close hFe matched pair on the two output boards together with new TR200 trimmers.
8. The two output boards with their heatsink mounted darlingtons were switched over, tested but with the same outcome.
that is were the project stands.
my question to you to make sure we are indeed talking about the same thing here:
do you suggest testing th heatsink-mounted darlingtons when you mentioned “output transistor” or are you referring to specific ones on board #5 ?
thank you for clarifying that for me
just went on to recheck the heatsink mounted darlingtons and made a shocking discovery:
Not only did
I find two with a negative test, but I actually went along with what was left of the pre-existing darlingtons when I got the BM......big mistake 😡
again and again I was looking at one of Beolovers blog & pics, restoring the output boards with its associated darlingtons.....
the PNP types should be on the right side together with the BD135, the NPN types on the left together with the PTC board.
mine is just the wrong way around.......can you believe it ?!
I am somewhat shocked at the moment and truly disgusted.....such a crucial error.....unbelievable !
will get on to it immediately and report the outcome when I received a replacement set.
Big thank you to you for kick-starting another transistor check.....
what I found did not amuse me at all........but it was worth it !!
will report back !
ALF:Hello SB, many thanks for coming on board......very much appreciated 🤗 a quick recap of events: 1. BM arrived as a ‘non working’ unit, most output darlingtons from the heatsinks were missing 2. A total recap of the whole BM was done, including the installation of two new sets of output darlingtons. 3. The two high wattage 5.6 Ohm resistors on the starting-up board were replaced - originals been way out of spec. 4. The no-load current adjustment trimmers plus the 2 emitter-resistors (0.18ohm) on the suspect output board were replaced. 5. No-load current adjustment on the “good” output board was possible but very touchy. 6. A switch-on test uncovered the “suspect output board” and triggering of either fault switch or/and current limitter circuit ?! 6. All transistors from suspect-board #5 were tested off-board 7. TR201/202 were replaced - thanks to a recom by John - with a close hFe matched pair on the two output boards together with new TR200 trimmers. 8. The two output boards with their heatsink mounted darlingtons were switched over, tested but with the same outcome. that is were the project stands. my question to you to make sure we are indeed talking about the same thing here: do you suggest testing th heatsink-mounted darlingtons when you mentioned “output transistor” or are you referring to specific ones on board #5 ? thank you for clarifying that for me ALF
Now it is getting interesting - this is what happened:
after swaping over the two boards #5 As John suggested I tested the suspicious board in its new position which was again negativ ☹️
after my latest discovery I rectified the mistake with the darlington set-up and it worked fine 😁
next step was to reconnect the previously working board #5 and ....... negativ - now this side/channel plays up ???
I will revisit again the darlington set-up associated with the previously working board #5 just to be sure.
if however that check does not unearth another mistake I would suggest it is not the board but related in another way to that left channel
or the starting-up circuit ?!
any comments ?
You had already stated that the (original) right channel output amplifier assembly did have a problem with the no-load current adjustment and, perhaps the DC offset? So I expect you have unfinished business with that one. Plus while you corrected the problem with the transistor installations on the heat sink you won't know if that (original) left channel assembly is fully functional yet.This whole ordeal is another reason why pictures are important. You looked back at my photos and found your transistor installation problem. If you had photographed before and after on your work someone probably would have caught that earlier. I always recheck my work by going to the photos of what I just did. There have been quite a few times where studying the pictures revealed a mistake. It is a valuable tool now days.
Another thing...I was under the impression that you fully swapped the output amplifier assemblies. Are you saying now that you just moved the left to the right but only connected the right channel (you didn't have both connected) when you rechecked the power on? So is the current output amplifier assembly sitting in the left channel slot failing the exact same way as the original left channel assembly?
something went astray here.....perhaps not clear enough explained by me ?
I swaped over the complete original left output-board incl its associated power darlingtons heatsink-mounted, now sitting on the righthand side.
no-load current adjusted and not triggering fault switch or current limitter - that is after correcting the position of the darlingtons!!
the original board from the righthand side sits now on the left with its associated heatsink-mounted darlingtons - that is the board with the lets say
touchy no-load current adjustment.
after the swap I only reconnected the original leftside board (now with the corrected mounted darlingtons on its heatsink) and it showed no trouble.
ok,
lets now look to the one that moved to the left side - previously not triggering any safety switch:
I joined (reconnected) that after the original leftside board caused no trouble and the two output boards should have been working without issues !
no, now when the two are connected the fault switch kicks in ?
just to be sure, I unsoldered its heatsink with the darlingtons and tested (as far as possible) all 6 for correct position (no negative findings were expected)
and shorts....no negative findings !
the board is still connected to the -/+55V and 15V supply together with P39 and the single ground connection.
turned on the BM and no fault switch kicked in, meaning the board is not under load.....no darlingtons are connected at present.
why should this board cause an issue now just because it has changed position as it was not doing that previously?!
is one of the darlingtons cracking under load ? Does not make sense to me!
I am having second thoughts about this left side - sure, it wasn’t working before because of wrongly installed darlingtons, but is the starting-up
circuit really out of the woods ?
In the meantime I am going to take out the board on the left side again and test all transistors off- board - remember TR201/202 were already replaced
with a hFe matched pair incl the R200 trimmer fir the offset adjustment!
a word about taking and uploading pictures......I absolutely agree, if only I can find a way of decreasing the picture size/file size when taking shots
with the ipad pro !!
I tested off-board all transistors of that board (the original righthand sided one that now lives on the left) - no adverse findings !
also I trust those associated heatsink-mounted darlingtons - all tested fine, no shorts.
Tempted to reconnect the darlington heatsink block.........😬
This is the output board in question without the darlingtons that currently has issues....or is it the board that has issues ?!
Something with the photo upload is not working here guys, sorry !
Sorry, its the file extension I am having trouble with
not suitable ??
Apart from the picture upload problem I went back to the output board as I haven’t checked the diodes:
all tested fine.....so, there is really nothing left I have not tested from that board.
i wonder if it is possible that one of the mounted darlingtons makes unwanted ground contact when reinstalling that heatsink block ?
once reconnected I will test it again but this time not fitting it into its designated position.