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
greeting all,
just finished with the recap of my BM6000/2252 - quite a job 🙏😳
but sadly it is still not working as it should ☹️
I can’t get the -/+50V from the power supply plus to make matters worse: one channel sounds very weak ?!
The maximum I can find are -/+37V which goes to the poweramp board 9.
But that should not be related to a strong and weak channel - looks like two different probelms?
The idle-current has been adjusted to 22mV for both channels as per SM ?!
what did I overlook ?
does someone care to comment with suggestions - that would be most helpful.
ALF
Hi all,
strange things happen but with that number of connecting plugs it is now playing on both channels as expected.....meaing it was obviously a connection problem ?!!
two things are still not right:
the globe on my DBT is still on....idle current is spot on and it sounds perfectly right !?
it catches all FM stations nicely but the DP1 that should display a steady frequency related to the station is not playing ball!
the frequency is displayed steady for a moment and then races up and down around that dialed-in station without anything been touched on the keyboard....?
some pointers would really help - thanks
If the power supply is anything like the 7000 and late 5000 series, there will be a DPST NC main power relay, which when activated puts the system in standby mode.
Low voltage on the + or - power rails can be caused by high contact resistance of the main power relay. That would be the first place I would look as both of my B&O vintage systems had dirty contacts, in one case causing enough heat to melt the plastic relay parts.
Other possible causes are poor connections, cracked solder joints, bridge rectifier or transformer issues.
¡No entiendo Español!
NEIN! Nicht Versteh!
Я немного говорю по-русскии но не очень хорошо... и
I'm not very good at English either! Maybe someday I'll find a language I'm good at?
Hi Keri,
thank you for your pointers - I will look into these issues.
already inspected as close as I could the solder joints on the uP board - no adverse findings so far.
the strange thing is as mentioned before:
the BM plays/sounds nice despite the globe on my DBT is still on......?
Hi All
I started scanning through archived posts in regards to the DP1 frequency issue subject......not much to be found except a monster post
by Sonavor/john exceeding the terms of refernce 😁
my BM still shows a “racing through the band” and I begin to wonder if it has something to do with the ‘prescaler’ and it chip(sj associated with it ??
if I am not mistaken Sonavor had a possible issue with that prescaler chip as well ??
perhaps he can shed some light on the issue ?? John,....where are you 🙄🤗
its quite “dark” at the moment...
Hi Alf,
That Beomaster 6000 project from 2012 (on the archived Beoworld forum) was ages ago and one of my first projects. I had a lot of help from the Beoworld Workbench group but never could get to the bottom of the FM frequency problem. Just when we were getting close the volume control motor gave out. I had no spares and other pressing things going on so I had to shelve that project. I later returned (with a spare Beomaster 6000) and swapped out the board with the microcomputer and frequency counter circuit. That was the quick and dirty way to fix it and the Beomaster has worked great ever since. I would like to someday go back and solve that faulty board but it is far, far back on my to-do list right now. Looking back at the issue I think I would approach it a little different. I should have trusted that the original circuit was fine. With the circuit malfunctioning after replacing some of the counter devices (including the prescaler) I should have looked for instability of the FM frequencies elsewhere.
John
Thank you so much John for taking the time to reply.
sadly in th absence of a,spare uP board my ‘dirty fix’ to the problem looks more like ignoring the constantly changing DP1 frequency display.......
unless some other beautiful mind comes up with a new lead ????
Martin might be snowed-under with too much mportant work....he usually points the finger in the right direction. That of course should not discourage
any other beautiful mind to come up with ideas.
perhaps the problem is not even on the up board to be found ?
Thinking about the next steps......
revisiting the supply voltages for the SN74xxx chips, which have to have a 4.75V minimum operating voltage as per datasheet !
if that turns out to be the case:
replacing the SN74LS93 and SN74LS393 chips and see what happens....
as all FM stations are stable when tuned in the issue has to be counter-related.
Ok, here is what happens:
at P2-1 are 5.3V instead of 6.5V !!......so, IC7 and IC9 only getting 4.45V supply voltage instead of the minimum required.
related to P2-1 is the volume dial illumination which should see 6.5V but.....instead its getting 5.3V being the reason why it is so dim !☹️
Now the big question:
where did I loose the voltage ???
The source of the 6.5 VDC is the power supply board (module 16) at P41-1. I would start there. The microcomputer +5 VDC comes from 6IC3 via 2P5-3 and 2P5-4. It is separate from the +5 VDC that powers 2IC7 and 2IC9. That +5 VDC does come from the 2D1, 4.7V zener diode. It does derive from the +6.5 VDC power voltage though.
Start with the power supply board and check the +6.5 VDC. If it is low then you will probably need to start disconnecting some paths that use that voltage to isolate what is bringing it down.
Oh yeah .... thanks John......been there already 😁😁. that is coincidence - I was just about to report back after measuring
on the power supply (board 16):
the frequency counter can’t work as 2IC9&7 get below the minimum required supply voltage - 4.45V instead of 4.75V !! Meaning no point replacing those.
looking at board 16: Base of IC1 is about 8V instead of 9V, base of TR1 is about 3V instead of 3.8V.
next step: check if the 10.5V at The +terminal of C1 (3300uF) are present ?
question is:
how likely do i have a faulty D1 or IC1 and which part plays the R4 trimmer ?
What do you get at P41-1 on the power supply board?
Hi John,
news are not so good:
p41-1 shows 5.3V and at R12 I can see 6.2V which is the same as what the + terminal of C1 and E of IC1 and the +terminal from the bridge rectifier D1 are getting.
Again, Can we rule out that D1 is faulty as this should deliver about 10.5VDC ?!
According to the schematic notes you should have around 10.5 V at the node of 16C1, 16C4, 16IC1-E, R12.You should see 6.5 V at 16IC1-C (or 16P41-1).The base of 16IC1 should be around 8 V.The base of 16TR1 should be around 3.8V.
Try adjusting the trimmer 16R4 and see if you can get the output voltage of the circuit to 6.5 V (at 16P41-1).
Exactly John, that is what should be, but.....
adjusting the trimmer in Stand-by mode I can get the 6.5 V at P41-1, however B of IC1 is 12.3V and B of TR1 is 3.5V
and at the nod of R12/+C1 it is about 10.4V
all these measurements happen in Stand-by mode only !!
if I turn on the BM the R4-trimmer has next to no effect on the desired 6.5V output, infact it breaks down to about 5.xx V.
the question remains, isn’t that circuit actually ok and the problem comes from another source as
the globe on my DBT won’t go out when the BM is switched on !
How much wattage of a bulb are you using in your DBT?
If you are into functional testing of the amplifier I wouldn't continue using the DBT. I only use it as a first power on protection device and a test tool if I want to attempt powering on an amplifier I don't know the condition of. Having a DBT bulb that has too low wattage will yield false results as well so you need to check that. It sounds like passed the usefulness of the DBT so I would remove it. You can take some intermediate precautions like not connecting speaker loads and maybe disconnecting some board connectors that aren't critical for the Beomaster to turn on. Once the Beomaster is out of standby mode measure all of the voltage supplies. With those tests passing you can power down and start connecting up some of the components you disconnected. Then check the power supply voltages again.
it bugged me all the time to see that still illuminated bulb - 77W - but wasn’t game enough to plug the BM
straight into a mains power point .
however i took your advice, plugged the thing into the mains without the DBT...and see 😳😳😳
the DP1 functions perfectly, no frequency flickering..,sound is great....so, I am - as usual - cautioulsly optimistic
in saying ‘problem fixed’ ?!! And all the recapping and trimmer channge wasn’t invain.
big thanks to your advice....🙏🤗🤗 now the long-term testing starts.
ciao