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 :-))
I am sitting over my "special friend" the BG 4002, not working......
Looking at the circuit diagram it should have 41V DC before OTR1 at 'OFF', 35V DC at 'ON'
It also lacks the 22.8 VDC supply voltage, measuring about 3 V DC lower as it should !!!!
Incoming V AC at OD1 is 33 VAC and outgoing 38VDC - is it a fair assumption that OD1, the bridge rectifier
might be faulty ??
according to the parts-list it is a B80 C2200 - available would be B80 C3700/2200 as replacements ?!
in case my assumption is correct could I use a B80 C5000/3300 as well ?
thank you kindly for your input
ALF
The low voltage is most likely because of a high load somewhere.Remove the load and measure again.The rectifier is just four diodes - why not just check if they are all there?Or put a scope across the filter capacitor and see if the ripple is 50Hz or 100Hz and all pulses are of apprx the same peak voltage.
Martin
The diodes seem all there.
ripple is between 400-600 mV - no specific frequency shown on the scope
however I stumbled into a strange finding:
when disconnecting the platter motor from ground I measured across the 'smoothing caps' (2 x 4000uF)
OFF-mode 41.6 V
ON mode 38.5 V instead of 35V
V mode 35.6V instead of 31V
the carrige moves across, 33rpm speed is on and the arm lowers automatically at 30cm record position
I can measure the amplifier output of 11.2 V and the 22.8 V supply rail is at 22.6V - these measurements occur with platter motor disconnected !!
re-connecting the platter motor prevents the automatic arm lowering and 33 speed and shows the 22.8V supply rail at about 19.8V ????????
what is happening here
Speechless ? Clueless ? YES !
Looks like I am not alone ??
I can confirm it is not the rectifier nor is it a faulty platter motor as I did change-over the motor.....
Same outcome !
The million-dollar question remains unanswered - why the voltage drop or current-leak ?
Prize-money after this week's lotto-draw :-)
I would check the transistors OTR 2 & 3. With the motor disconnected they will not draw as much current but could break down with the motor connected and increased current draw.
thanks for your suggestion Jim,
already replaced both transistors :-) but:
no change I am afraid, unless those parts I received were faked parts ?!
simply don't get it - just for "good measure" I am going ahead and replace the rectifier as
only the OFF voltage showed about 41VDC - ON at 38VDC and V mode at 35VDC are way to high......
there must be a simple reason for that, or mustn't it ??
cheers
If your Beogram has a 2,2uF tantal capacitor on the board under theoperating panel, I suggest you check it and the related diode.
Negativ
Diode yes plus a 100uF/25v cap and the muting relay........but no tantal 2.2uF.
Hi Alf,
Reading up on tour post my initial thought is that the motor is drawing to much power, could that be the cause of the problem?
searching on the net i found this:
http://beolover.blogspot.nl/search/label/Beogram%204002
Marc,
I did change-over the motor to eliminate it as a possible source of the problem.
So far not even our truly treasured 'B&O super guns' provided a promising lead - that is the disappointing
Part - the good part is the 'brain-storming session' is still open and the best is it is 'free entry'
excluding Drinks :-)
I am aware how difficult a remote diagnose is without having that table on the workbench, but......
The devil is hiding somewhere !!
Have you checked the 2 caps for the motor OC3 & OC4?
Alf,Electronics mechanic is a 3½ year long education with several school levels etc.Once educated, you can go out and build up experience.Repairing the older B&O things can be tricky, it's far from any run-of-the-mill "Whatsthebrand" stereo andit often takes a rather high level of experience and practice to nail problems "just like that".Don't expect to be able to repair any old fault in any old B&O just because you went to tech school.Beogram tangentials can be some of the more technically "nasty" ones due to their circuitry and theircombination of mechanics, electronics, switches, optos, sensors etc.Combinations for which there are no school, no classes or education.Even some experienced repairshops reject repairs to these decks because they find them toocomplicated, involved and/or time consuming (and/or difficult to source parts for).And by their nature most decks will need a more thorough restoration rather than simple repairs by now -which only makes matters worse.Here in the forum we can give you some ideas and tips based on the info, descriptions and symptoms youprovide, - we enjoy doing that - but we can only get so far and we cannot educate you or give youthe instruments, skills, tools etc. it takes to "just do it", let alone provide you with thedifficult-to-explain "sense and feel" for circuits and mechanics that's often a key factor. The problem in your deck could easily be something simple - it probably is, but how do you know whereto look and how do we know where to ask you to look for us.There is no doubt in my mind, that I would be able to repair your Beogram if I had it on the bench here -and so would other posters in this thread - but without the sense, touch, listen, feel and smell, I willhave to limit my input to making educated guesses based on previous similar cases etc..For almost every possible fault you can think of in a Beogram like yours, there could be several possiblereasons - some are commonly known, others rare and again others still to be discovered.
Are these threads about the same deck:http://archivedforum2.beoworld.org/forums/t/15656.aspxandhttp://archivedforum2.beoworld.org/forums/t/20454.aspx ?
If so, with all due respect, the problem could have been introduced by you and not be from "natural causes".When you can no longer assume anything - those are often the more difficult situations.
Thank you for the sobering words :-)
Do I detect a hint of critisism ??? Well, I am aware of most of these things - would not cross my mind
To take the table to a repairer as I may even know more about these machines - certainly not the
Run-off-the-mill thing - damn right !!!!
Did I introduce the problem ?? Sorry, I can not answer that !
No one should feel under attack by my post - the disappointing part was addressed to the fact the table
Is still not working but certainly not directed towards any of our experts here - just in case that had been
Misinterpreted !!!!
I got involved with these machines over the last 2 years and learnt a lot during that time considerring
From whereI I started from - thanks to interest, initiative and help from knowledgable forum members.
I intend to further develop and any help is always much appreciated :-)
It is a desert here in repair-availability terms - there is no other way except throwing out these lovely
Machines - I am not going to do that.
Cheers ALF
the first post is a mix, the second concerns the same table.
let me repeat what the current situation is:
you can operate the table perfectly without connecting the platter motor - spin a record by hand
and everything will work fine till the run-out groove - arm lifts, carriage returns table switches off !
what else can I possibly say ?
I can measure the voltages as per circuit diagram.......the only thing I can see as being odd is a far too
high 'ON' voltage, reading at almost 39 VDC and 'V' voltage, reading at 35.xxVDC plus OC3, reading at
about 5900uF.
yes Jim I did:
OC4 reads about 160uF
OC3 reads about 5900uF
Am i glad to just have a BG1900 which speed control relies on 2 magnets inducing a break force on a copper dish mounted on the drive motor!
The only problem with these is that the hinge on the right side breaks...
I went over the schematic, which won't help you because it didn't help me either but still somehow i suspect the motor because disconnected there is no problem and it only appears with the motor connected.
But that's just stupid old me!
what i would do personally is check the current draw of the motor, just to get an idea, shouldn't be more then a couple of 100 mAmps, maybe some one here has a value for you to compare?
But then again, i am not an electronics expert, not by far!
wish you success!
Marc
Alf, Does the motor spin when you turn it on and have you looked at the sine wave with a scope?
Also can you check the leakage of the caps? Or any other specs? My schematics show a 4000uf cap for the motor do you have a replacement for your 5900 cap?
hi Jim,
yes the motor spins perfectly, showing a smooth sine wave - as expected !
I fitted a complete new cap package supplied by Rudy-beolover and it came with a 4700uF instead the specified 4000uF cap - I suspect it is difficult to get in that physical size ?!
I measured mine off circuit at about 5900uF - not quite sure how dramatic that impacts but will replace it with a new 4700 uF cap.
thank you kindly for engaging with that problem - any help is much appreciated.
Have you seen this site?
http://www.condoraudio.com/wp-content/uploads/Projects/BeoGram-4002-6000-Turntable-Restoration-Repair.pdf
Yes,
I have seen red and studied that post - thanks:-)
In the meantime I did replace the rectifier - just to be absolutely sure - no change !!
Yes, i barked at the wrong tree.
As this model was a US model I fitted a european transformer with the voltage selector to avoid
Using these step-down transformers but cannot see how this possibly would contribute to the problem ?
Anyhow, nothing is off the table - and yes Martin, should you read this - I am absolutely convinced
You would have found the culprit and brought back this lovely table to former glory.......but it's a looong
Way from Australia to Denmark !
Still happy to read your ideas, pointers solutions....
Cheers
Klaus
Scratching my head, I remember a problem like this on a BG6000 with the AC motor.
There are so many worn-out components on the main PCB, that just a recap is not even the start of an effective solution.
Firstly, to confirm that this is the same problem which I had, do the following:
Connect your Beogram via a DimBulb Tester.
The DBT mains bulb (60-75W) should not illuminate (or may be very dim), until the solenoid activates.
Then the bulb illuminates.
If this is what happens, you'll need to replace:
1. these transistors - make sure that you have good replacements and NOT counterfeits TR14, TR15, TR16 - you'll probably find that their hFe's are shot.
2. replace the large motor capacitor with a 220uF BiPolar 105-degree unit.
3. replace all the poti's
4. Go through the SM adjustment for the "Voltage for drive Motor" (motor phase), using a scope, DMM, AND the DBT.
While adjusting the poti, you can see the immediate consequence of the motor out of phase by the varying brightness of the DBT.
It becomes very clear, very quickly, where the optimum adjustment is.
5. Do the "Detector Arm Sensitivity" adjustment, still with the DBT. You can see where the poti loads the circuit, and the DBT illuminates.
Of course, I may be way off base, and the only dead-straight analysis I could give you, would be if the machine was in my lab....
Menahem
Thanks Menahem for your suggestions !
exactly that happened - the moment the arm lowers the dbt comes on and stays on until the arm is raised again!
all this only happens with the platter motor disconnected !!
TR 14,15 and16 have been replaced hFE all good as tested before.
platter motor voltage has been re-checked and adjusted with a scope.
i also replaced OTR4 , the TIP41A ====>. No improvement !
all potis have also been replaced.
the moment I reconnect the main motor the arm only moves across without lowering plus
the solanoid can not be activated at all.
simple fact remains I can not identify the load that pulls down the voltage ?
i feel the solanoid must draw too much current ?!
i should get 3.5V at E of OTR4 when lowering is activated but only get about 2.45V instead.
i do not believe you way off the mark at all - i just can't see it but believe it will be a simple solution
as it is so often looking back 😳
So, you're saying that you install the platter, and then the tonearm won't drop.
I saw that once, and the problem disappeared when I put on an LP.
Couldn't explain it, but it worked. Try it. Just for the heck of it.
If not .........
Are you certain that TR14, 15 and 16 are correctly installed - NPN or PNP? And, you should have hFe about 250-350.
What's the voltage going into the lamp for the tonearm sensor - measured right under the tonearm - when the tonearm is up, and when the tonearm is down?
Have you done a solenoid and damper mechanical adjustment, including cleaning the damper cylinder?
The damper could be causing a back pressure.
Keep the DBT connected throughout your testing - the intensity of the lamp will tell you if you're making progress.
Disconnect the solenoid coil, operate the above test as before, measure the voltage, and check if the DBT still illuminates when the tonearm would be down.
If the DBT does illuminate, then the problem is NOT the actual solenoid.
Firstly, I went back through my 4002 AC notes about 15 years, and found this:
Bus Voltage improvement, after exchanging these transistors (even though the originals were still "OK").
Transistors can check OK under a test meter, and then fail under load.
TR3 TR4, voltage up 0.3V
TR5 TR6, voltage up 0.2V
TR14 TR15, voltage up 3.1V, from 23.7V to 26.8V
TR26 TR31, voltage up 0.15V
Also these
D43
8.2 ohm 5W is hot - underside of a smaller PCB, IIRC .
R53 R56 hot
Your choice if you want to do anything about those - I would recommend it.
Next, your old big bad capacitors.
You MUST change them, EVEN IF the capacitance "looks" OK.
I did a BG4000 thread (which I can't find now) showing a DIRECT comparison on my scope of the AC Ripple current of the old original B&O caps, and the same ripple current after installing new capacitors.
With the new capacitors, the ripple current was HALVED.
That's a lot of energy (heat) which was wasted with the old caps.
Nichicon GU is a first-class choice for those 5 big caps, and Nichicon EP for the BiPolar.
There are NO audio-circuits in these BG's, so no need to be crazy and look for exotic audio caps.
Just DO it!
Let me answer this reply first.
all I did was without the platter present as no platter should have the same effect for the detector arm as a record present ?!
the two scenarios are with the main drive motor disconnected everything seem to work fine, meaning carriage moves to the 30cm record point
solanoid gets activated and arm lowers - while this is the case the DBT lights up gently and stays on until arm goes up again !
the second scenario is with the motor connected - in this case the carriage moves right across and returns to its resting position.
during that move the solanoid can not be activated !
TR14 and TR15 show a hFE reading of about 321, while TR16 shows about hFE 81 - all those are NPN types.
OTR4 - TIP41A - showed hFE of about 31.
with the main drive motor disconnected I get. 22.3V at B of TR10 - motor connected I get 18.4V at B of TR 10
with motor disconnected I get 11.3V at C of TR11 - motor connected I get 8.1 at C of TR11.
the lamp of the detector arm showed 5.7V with motor connected and 6.3 with motor disconnected.
when the solanoid gets activated the damper cylinder moves freely - no sign of any back-pressure at all.
if I disconnect the solanoid coil I can only lower the arm manually but will try !?
Menahem,
the big old grey cap package has been replaced - all !!
as for the other mentioned TRs, Rs and D
I am curious and will replace those and keep an eye out for their hFE readings !
will report back about the outcome of the operation.
I completed the work you suggested, even included an earlier suggestion of fitting matched pairs of NTE transistors fot the carriage motor to reduce heat.
the outcome of all this is sadly disappointing and after lengthy reflection I have decided to part-out the BG4002.
it was a journey mostly around in circles - enough is enough.
it is very sad as it really is a nice table but unless you swipe the mainboard clean - totally clean I mean, it would only be more of a mix of old-new
components, introducing new faults.
let me thank you for your input - we can't win them all !
Wow, sorry to hear that.
I wish I could have been able to help you more
Normally, I do a complete overhaul of the main PCB, before starting work on all the mechanical sub-assemblies, which includes checking all the semiconductors, resistors, etc, etc, which are normally bypassed in favour of only a recap. That PCB is much more than just a recap.
Send me a PM of what you're going to part out - I may take some parts.
If the physical condition of the Beogram 4002 is good enough to merit restoration then I would not part it out. The electronics in it are discrete components. There are no complicated, multi-layered circuit boards or anything like that so it should be restorable.
The approach I would suggest is to isolate the specific trouble area and not jump to various things in the turntable. If you have a fully operational Beogram of the same type you could swap parts (just one thing at a time) where you do the swap, check the result and then swap them back. That should result in the problem part being discovered. If you weren't so far away I would offer to do that for you but I think the shipping cost would be prohibitive. John
Hi John,
sorry for getting showered with replies, but.......
maybe the parting-out idea was a bit premature, however I have to stress once again that I spent soooo many hours on that BG
my enthusiasm towards that one is at it absolute low point at the moment - perhaps a revisit in good time ??
There are so many new components on that board, which now looks more like a battle ground - the only way seems a complete
clean-up and start from scratch ?
To make decisions even harder, it is in very nice condition indeed which makes it so difficult for me to follow through with the parting-out idea !!!
it is resting right now - main thing is it has a dry roof over its "head"
what a pitty I am so much closer to a desert than a B&O expert !
damn right about the shipping cost though !
kind regards