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
Hi All,
its sometimes really good to have a donor unit at hand.....
as today, the fm-signal on the recently restored BM8000 sounded distorted, no matter which station
and the volume of that signal was quite loud even at vol setting 1 ?!
after checking that other inputs are ok I decided to swapp over the fm-related boards #2 & 1 from the donor unit and everything sounded fine again....😁🙏
but,.....
where to look for the most likely problem source on those two boards ??
as I have decided to go for another restoration project I want those fm- boards to work again.
the tuning voltage was set correctly.....other trim pots on the tuner boards I won’t dare to touch 😳
the donor unit is in far too very nice condition - so, its worth it to put in the work.
could someone throw some pointers in my direction.....pleeeease 🙄
ALF
Just had another look at the SM circuit diagram 1:
would it be a good start checking that OP amp 2IC6 ??
that one is handing over the FM signal via P10/pin1 and 4 to the preamp - board #3 P19
Hi ALF,
Is the distortion in one channel or both?
2IC6 is a good place to start. What are the DC voltages on the chip?
I had a TL072 fail on the filter board 4IC2 on a BM8000 for no apparent reason, it was distorting badly. It failed after I'd changed all the caps, I replaced it with no other changes and it was all good.
Regards
Lonnie
Hi Lonnie,
the distortion was in both channels....all fine after I swapped boards.
in the meantime I replaced 2IC6 but won’t be able to test until all other boards are done.
let’s hope it did the trick ?!!
only the processor board to do (i hope) and thinking about changing the two crystals as well while I am at it ??
they should both be short-wired before being put in, right ?
will keep all posted
Hi Alf,
I wouldn't change the microcomputer crystal oscillators unless you know they are faulty or doing a restoration where the owner lives far away and shipping costs are outrageous.
The microcomputer board is easy enough to get to and can be done later if necessary. Why risk it when you don't have to?
If you end up having to I believe I sent you links before to the details Rudy and I have posted on the Beolover Blog. You can't just change only the crystal oscillators either. Each oscillator has two capacitors that control the oscillator frequency.
John (sonavor)
Hi John,
as always, good to hear from you 😁 thank you for your advice - point taken !
going through Rudys blogs though it just struck me as ‘one of the things to do’ when a BM8000 restoration is under way?!
down here it is not as easy to get access to those parts, so I grab it while I can - yes, the two crystals with two pairs of 18nF caps 🤙😁
will store them just in case.
the processor board needs attention:
the memory chip seems to no longer does its job as FM stations won’t get stored,
the 22uF cap needs replacing and I was going to
provide the two big processors decent tulip-style sockets........
that is it for now - looking forward to read further comments, ideas etc.
As I said, if the BM8000 is being restored for an owner that lives somewhere far from us, where shipping cost is a factor (i.e. USA to Australia), then we change out the oscillator devices as extra insurance.
John
Bad news I am afraid:
fuses blowing on the #7 board and I fear the standby transformer has a short ?!
if 3OT1 is disconnected from #7 board fuses stay on, if reconnected fuses blow !
it is not the power supply board as after disconnecting P52 fuses still blowing 🤬😢
looks like I have to chase the almost impossible replacement for that standby transformer 😢
unless one fellow Beoworld member can help ?
That smaller transformer is for the 5 VDC and +-15VDC.
I am not presently in a location I can check anything so I'm just going from memory. There are other things besides the small transformer that could cause your problem. You could always pull the small transformer and check it out by itself.
yes, understood , it is for those 3 voltages.
the transformer is disconnected from the PS board #6 !!
the moment the HV side of the transformer is connected to board #7 the fuse blows
if the HV side is dis-connected the fuses stay on. The HV is getting about 238VAC, coming straight from the AC mains.
I believe board #7 is doing its job.
perhaps there are other sources causing that problem - sadly I do not have the equipment to do any further testing of that stand-by transformer.
are you be any chance implicating the main transformer ?
No, both transformer s are "main" transformers. The large transformer is for the amplifier +-55V rails. The smaller transformer is for everything else. It sounds like something that gets its power through +5V or +-15V is shorting and blowing the fuses.
You could try disconnecting the power cables from some of the other boards to eliminate them as the source of the problem. For example the FM boards then the preamp board.
I am trying to follow John, but
if P52 is disconnected from the PS board #6, which is fed by the small transformer, how do you get power
through the +5V/+/-15V regulators to other boards ??
plus, if the HV side is connected to the small transformer and P52 is not connected to board#6 how can this blow the fuse unless
the small transformer itself has a short ?? i am really trying to understand and shall have another look !
Sorry to say John, but
after disconnecting all power sources from board #6 the fuse still blows the moment I reconnect the HV side of the small transformer !
I am reasonably sure that transformer has a short ☹️
I would not hesitate buying one if I can find one.......do you have a spare to sell ??
Is that part# 8013222?
Martin
No Martin, it isn’t 🤬 it is 8013227
All I can say is : TYPE 1903 !!!
a brief explanation:
with no additional information from the German seller the unit has been bought from Germany, earmarked as a donor unit originally.
i did not even assume for a moment that this would be a US model, running on 120VAC as there was no US plug attached.
Thanks again Martin for being the catalyst in asking for the part number, only then it triggered me to have another look in the SM ! 😳😳😳😳
silly mistakes do happen.
all fuses are now staying healthy.
I am however happily reunited with the old issue of ‘no audible sound’.
after adjusting the ‘no load current’ and DC offset there was hope, but....nothing so far.
one usually hears a relay clicking when the power plug is pulled but that is not always the case.....meaning when I reconnect the unit the output
seems full on without actually using the keyboard or remote. They other issue is the failing ‘store’ function despite having replaced the associated IC
on the uP board!
so, there are still a couple of issues to follow up.
i would most certainly appreciate all the help I can get 🙄🤗🙏
It now sounds like your +-55VDC rails are not powering up. Check your +-15V supplies. Also check the two 5.6 ohm resistors on the startup board.
Has it been wired for 230V now then?Also the large transformer (not all can be rewired)?
The +/-15V supplies are present and it sounds like the 55VDC rails are powering up, judging by the double click of the relays ?!
i will - to be sure - check again tomorrow.
and then there is still my special friend, the tone/filter board ! 🙄
No, not while I had the unit.
i do recall the unit came without a power plug, something some foreign owners do - it’s my best guess that it was most likely a US plug.
I am using a step-down transformer now, which works quite well.
I am not sure whether the small transformer can be set for 230V operation ?
to check the big one I would have to pull it out, which would appear to be a rather BIG job
and then, how to rewire ?? Unless you can tell by the serial number ??
Type 1903 is the 120V US version.The transformers can not be rewired.
Despite soft-start circuit Beomaster 8000 has a very high rush-in current at power up.Your step-down transformer must be able to handle this.
Also, you just reported that you hear the relays click....so do you have +-55VDC on the rails now?
Sorry for the delayed response - need to sleep occasionally 🥺
yes and no.....I only have +/-51 VDC, measured on the big reservoir caps.
but still no sound, neither via FM nor TP2 ☹️ But I can hear that static prickling noise when turning the Vol wheel ?!
mystifying....
ALF: I can hear that static prickling noise when turning the Vol wheel ?! mystifying.... ALF
I can hear that static prickling noise when turning the Vol wheel ?!
The crackling noise when the volume changes is a symptom of the DC offset compensation circuit on the Filter & Tone Control board for the volume control device. Each channel has an adjustment trimmer there. There is a procedure spelled out in the service manual for it.
That being the case, it sounds like the volume control to the output amplifiers is working if you are hearing the crackling noise.
That means the problem is with the source signal getting to that volume control circuit. I typically suspect cable connection problems first in this case. Always mark all of the cable connectors with their target connector designation using a Sharpee (black marker). It will save you in the long run. Make sure the cable plug that goes in the left, upper side of the Filter & Tone Control board is plugged in.
If the cables are all correct then try swapping out the preamp with one of your good ones. After that, the Filter & Tone Control board.
Pre-amp loops installed?...
Hate to make the same mistake twice Martin, .....🙄
you mean the two metal jumpers on the left outside....yes, they are in !
The crackling noise doesn’t worry me so much at the moment - yes, I know the procedure. The tone/filter board got even two new trimmers for that 😁
what is also unsettling is the fact that the signal strength meter for the FM isn’t showing any sign of life, MPX however comes on ?!
I checked the FM output at 2IC6 pin8 - should be getting +15VDC - and pin6 - should be getting -15VDC
I measure -14VDC at Pin8 and -6.4VDC at Pin6 although the +15V/-15V are getting to the board....meaning I have to take out
board #2&1 and check again.
in other words, one FM channel output - OP amp is only getting half the required voltage supply ?!
I did check the cable connections and will do so again.
swapping board#3 did not achieve anything....same with board #4 ☹️
Hope you are right with the cable connections 🙏🙏
I would hold off messing with the FM boards for now. Work on getting Tape 1 & 2 source inputs functioning. Once you reach that point you can return to the FM board.
Check over your source input box and wires. Someone could have mucked around with that. Verify your Tape source signals successfully reach the preamp board. Then continue from there.
Well, some partial good news:
somehow I got the right channel working, using TP1 and 2.
getting some hiss on the left speaker but that’s it !
so far no findings on the input cage and preamp board. i have gone through the cables once again but everything is ok.
the switching between inputs is also working. I have a couple of AD7110 ICs of chinese make......which i have not tried out ?!
I believe both output amps are working, having adjusted the no-load current and DC-offset.
yes I know, sometimes one can not see the trees in a forrest !
for now I have to rest after spending half a day “messing around” on the beast.
Ok,
saturday.....workday again !
couldn’t help to get back to my special friend the tone/filter board : game enough to change the vol attenuator chips AD4110KN one after another
And see........both channels have audible sound - hurray 🙏😁
so, another positive step in the right direction.....next to that awful crackling noise, which is quite audible when switching inputs and vol adjustments.
an initial “blind” adjustment of trimmer pots R146/246 delivered no relief and I may - as the SM suggests - disconnect R243/245 and R143/243 to extend the trimmer range.??
will be back 🤞
Sadly the resistor trick - lifting 4R143/145 etc - has no impact on that static crackling noise when switching inputs and adjusting the volume.
I decided its time to revisit the uP-board after studying some of Beolover’s blogs reflowing a number of suspicious joints.
the memory issue, storing FM stations, seems cured and the static crackling noise is much better, although not entirely gone.
an interesting but annoying new issue turned up:
When turning the BM on the balance setting is right over to the left channel - I can correct the setting on the tone/filter board again, fine
all sounds normal.
switching off the BM and start again the same issue is present ???
looks like I have another inspection of the uP-board checking on the soldering !??
sadly still no “sound” from the tuner ...... as said, I can dialing in FM stations, but silence is the answer 😡
desperately need some assistance here - so far I only replaced 2IC6 with no outcome......
anyone ??
Jacques
Thanks Jacques - problem solved🙏🤗
Looks like I arrived at the perhaps last major roadblock ?? !! the tuner !!
a quick recap:
FM stations can be tuned in and stored but no audible signal output ??
MPX lights up once a station/frequency is detected but signal strength meter is not moving
as mentioned previously, I should measure +-15VDC at 2IC6 pin8/6 but it is not there.
these voltages are however present at 2P8 - 1 and 3 but somehow don’t get through ???
I also mentioned earlier the replacement of 2IC6 !!
who could give some helping advice here ??
Well, check for broken tracks. I’ve had some broken just at the limit of the solder joint, quite impossible to see even with a magnifying glass.
Some bottom plate screws are long enough to reach through to the underside of the tuner boards.One screw sits exactly where it can cause the tuner to go silent. Worth checking,Also, check or replace the two boards inter-connecting plugs/sockets. They may look fine but they usually aren't.
Ok, time to report back:
first, no screws sighted - good news
where the boards #1 & 2 connect I inspected the solder joints again, two looked suspect and were reflown - the plugs itself git the deoxit
treatment.
surprisingly the two tantal caps 2C21 & 23 were put in the wrong way - I wonder whether in this instance it is important or not ??
naturally I replaced both and pit them in according to the circuit diagram !!
next I discovered the connector 1P2 was loose, not providing a secure connection to 9P84 - reflown and back in business.
I also verified continuity between 2IC6, Pin8 and its +15VDC supply, again a suspect solder joint was detected and reflown.
with all that activities finished it was time to put the tuner-boards to the test.....success, FM has been restored 🙏🤗🍷
Detecting suspect solder joints is indeed a big task and even bigger is it importance....!!
still a few “building sites” to rectify - Not yet the clean bill of health, but out of intensive care......wonderful 🤙
I shall be back with another report, for now:
big THANK YOU to all actively involved members, contributing their knowledge & experience.
Well done Alf 👍🏻👍🏻
when is a project ever finished............? I won't answer that !
finally had the courage in a moment of madness - had to wait for that though - and attacked the faulty display.....!
this had to be the most punishing job I have ever done...YES, it was.....but now it looks like that....still waiting for the black glue
to seal and close the three displays properly, however a giant leap for ME - believe me!
I have attached a couple of pics.......enjoy......you should try it one day.
at this point one thing is bugging me and that is the failing memory for the FM pre-sets - I replaced the memory IC in the uP box
but sadly that did not help ?!
perhaps one of the famous fake ICs and/or perhaps another source.
would be great to get some suggestions / pointers to help....anyone ??
thanks ALF
and another one.....