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 đ¤
my BG4000 has issues with a faulty engaging servo !
following the faul-tfinding flowchart of the SM all is pointing to the pair of ORP61.
they differ quite substantial in their resistance reading:
under direct light (bottom side) they show about 24kOhm and 16kOhm
under direct light throught the top slots they show about 160kOhm and 105kOhm.
no matter how I adjust the servo (light intensity, diagphram height) it is just not working.
both ORP61 are getting about 23VDC, the light source is working fine and 1D7 and 1D13 are fine!
perhaps there is something else I may have overlooked but with those differences in resistance value
I can not imagine it would ever work ?!
comments are warmly received - I also posted a wantd ad.
ALF
Hi all,
getting a response from Martin - he does not believe that ORP61 parts are to blame but pointed me
to a signal check at the H- bridge.
according to the circuit diagram I should be getting 0V both at E of TR28 and TR31 when ON and ^ are activated ?!
sorry, I do not have the 0V on either - one reason being is the carriage slowly moving outwards đ¤Ŧ
in kept adjusting the diagphram height, shutter position and light intensity....just won’t do it.
I will revisit the diodes and test the four transistors involved with the H-bridge.
so far I only managed once to play an entire record, however after reaching the run-out groove the arm did not lift and return.
Ok,
I finally got the carriage to stand still đ so I can actually verify the voltages:
E of TR28/31 shows around 70mV, not 0V as per CD
B of TR27 is varying between 45 to 90mV, not 0V as per CD
B of TR33 is around 150mV, not 0V as per CD
B of TR25/34 show 0.69 to 0.72V which I think is ok.
to sum up: 0V at ON and ^ activated are not present âšī¸
I guess it is off to a transistor check/test off board !
Hello Klaus.
Is it a silly question,but have you checked the tracking servo switch on the solenoid assembly?
The '4000 has a switch to enable the tracking servo once the arm has lowered.
It connects the two tracking sensor ldr's into circuit.The contacts can and do become oxidised,so reducing the current through the ldr's,and limiting the tracking sensitivity.
Nick
Hi Nick,
yes, thanks for reminding me - I did indeed carefully sand those brass contacts - sadly no positive outcome to report.
just ordered a new servo belt from Martin and will see what that changes?? If anything ??
the carriage control does not perform as usual at all - does not move up to the drop-down point, arm drop right after activating ON.....
I tested TR26 to TR33 off-board.....all good - also checked the diodes D7 to D14, but not off-board.
the main board has not yet been recapped...should that impact in the way the carriage performs ??
You should have 24 volt at the collector's of TR27,28,31 and 33.Are you confident that the 24 volt supply including it's reservoir cap is ok?It may not be supplying enough current.The reed switches are alway's suspect too.
Martin's "v" belt's are a good investment,they provide better traction than either a square or round belt.
Is the carriage motor seized?
The carriage motor drive circuit is pretty robust,with the motor forming a bridge between the two amplifiers.When a direction button is pressed,the circuit becomes active and applies the supply voltage across the motor in one or the other polarity to drive the carriage in or out.
Well,
the 24V supply is showing about 23.4VDC - and that is the case at all suggested Collectors of TR27, 28, 31 and 33.
the two reservoir caps 0C1 and 0C (2000uF/15V) measured actually about 3140uF and have been replaced - thanks for pointing this out !!
sadly, that did not yet show any improvement in the carriage performance.
the carriage motor is running freely - I can hear it clearly when its naked pully (no belt) spins (both directions).
as said, a new servo belt is coming but this alone won’t fix the issue. I am also not yet convinced a complete recap of the main board will do it ?!
question is though, where to from here ???
Just to clarify,are you saying that the carriage doesn't move,but the motor spins ok?
If so,does your '4000 still have it's original plastic carriage spindle pulley.If so it could be simply spinning without gripping the spindle?
Can you undo the securing screws for the spindle pulley bracket,and see if the carriage can be moved freely by hand?
Otherwise,you could try bypassing the 24v supply reed switch to see if it's reducing the supply under load?
I don't think that your problem is on the main board,but it will almost certainly need attention after you sort out the above issue.
It's not necessary to completely re-cap the board,but replaceing the electrolytics,particularly the 'tant's will improve the operation overall.
The speed change relay will probably be intermittent too,and of course the presets will be oxidised!
What happens after ON is activated is a mm long move of the carriage inwards, just enough to clear the on/off nipple switch.
if I do that exercise without having the servo belt fitted the platter motor starts spinning and so does the little servo /carriage motor.
Yes, the spindle pully is the old plastic one - I still have a metal replacement I could fit but the carriage was moving freely towards the drop-down point
before all that jazz started but will double check that pully/spindle issue.
when I mentioned recapping the main board I was only going to replace about 10 or so elcos and the few tants.
I did deoxit and fine-sanded all brass spring contacts in the control panel and underneath the nipple-switch assembly that has the carriage run over it.
To rule out any contact triuble, meaning I do not expect any issues from that corner !!
it is just absolutely puzzling that all of a sudden it would no longer work without any obvious reason ?
what is going on here ??
This seems to be a start up problem then,rather than just a transport problem?
The slide switch that you refer to as "start/stop" is in fact just the stop switch,and it seems that if the turntable motor is running once you move the carriage inwards from that switch,the problem is to do with the logic control of the power supply at start up.
I think you will need to double check the operation of the "nipple" switches as you call them under the carriage mech.The stop switch should remain closed once activated.The power supply is controlled by a flip flop circuit which in turn is controlled by the logic system.
I have the training course notes for this machine,I may be able to copy the relevant pages and e.mail them to you,but in the meantime,check those switches and the reed relay's again?
Yes indeed,re-cap as you plan to,but I would overcome this other problem first?
You may send me those training course notes too, if its not too much trouble ;¬)
Craig
Yes Nick,
of course, it is the stop switch (what I actually meant) đ
I only mentioned the recap as it usually comes up as one of the “must do things”, but it was not on my agenda straight away.
well, the relevant course notes would be fantastic - thanks for your thought Nick...happy to receiveđđ¤
see how things progress....đŗ
This is also an interesting example of an issue where the fault-finding flowchart in the service manual may!! lead you to “nowhere”
or masking underlying issues:
quote: .....is the carriage moving inwards ? N is OM2 running ? Y is carriage blocked ? N. ===>. Repair spindle, fit belt !! đŦđŦ
it is not that easy and straight forward đĸ
so, I am looking forward to study Nick’s training course notes he offered.
may there be some light at the end of the tunnel.
The Beogram 4000 can be a bear to get set back up properly. I remember on one of mine I was having some sort of logic error. The contacts were all good and the parts all tested good. It turned out to be a contact problem when everything was reassembled. A contact was not making good contact. It took a bunch of iterations to tweak the switches before mine was fully working again.
Too right John !
to put it blunt: right now I have absolutely no idea what is going on with this table ?
there are only a finite number of mechanical contacts to check.
I double and tripple checked they all provide good contact - all have been cleaned as much as it was possible.
the old servo belt had it and I am awaiting Martins shippment for a new one to put on.
why the carriage only moves a very short distance and almost immediately after drops the arm is puzzling.
don’t tell me there is a logical error ...... pleeease.....as the original problem was a non engaging servo.
at that stage the carriage was traveling nicely up to the drop-down point.
a mystery, or is it not ?
Hi to all interested parties đ¤
back on the project, but it looks like an uphill battle đŦ
gone through Nick’s training notes.....
completed the recap job......even a new servo belt has been fitted....however new drama unfolded:
carriage still does not move to the 33 arm-drop point but stops after about 1cm and platter motor now starts on 45 instead 33rpm ?
back to the fault-finding flowchart of the SM......and following different scenarios:
Q4 = 0.9V,considered ‘high’ YES, manual speed-change works, low SI impuls before reaching 5.9V YES. ==> checked & replaced1TR20....no change
consider lown SI impuls missing ====> replaced 3IC4 flip-flop......no change
Q4 at 0.9V considered ‘low’, 1TR6. Collector < 24V, reed relais & position indicator light working ===> checked & replaced 1TR5 and 6....no change
all makes no immediate sense to me ?!
observation: 24V and 6V supplies a tick low at about 23.2V and 5.9V.
something here has gone pear-shaped pretty badly.......but WHAT ?
Just as a quick check make sure you replaced 1C15 in the correct polarity when you recapped ;-)
craig
Interesting thought Craig, but No.....1C15 is fitted correctly đ
problem not yet solved - back to the training notes and the fault-flowchart in the SM đ¤Ŧ
Back on the work bench:
the table starts at 45rpm instead of 33rpm.....well, for some strange reason SI does not preset 3IC4 the correct way and Q4 is at about 4.9V (high)
I just don’t know why ?
the SI signal shows exactly the curve shown in the training notes !? Yet it does not seem to preset the flip-flop correctly.
just wondering how crucial 1C15 is, specified at 10uF/6V - I replaced the old tantal while recapping with a 10uF/16V ???
back to the train8ng notes......đŦ
Alf
I have just been down this road, my problem turned out to be the 6vdc rail not delivering....and oddly enough I was measuring around 4.9vdc as my HIGH signals too.....check your providing the full 6vdc power at your logic IC's pin 7, bear in mind its the IC itself which provides the power outputs.
One can never be too sure Craig,.....
good point, so I rechecked the 6V supply at all 3ICs (except 3IC9) and all had -depending on the choice of ground point - either about 5.98V or 6.00V
so, all clear in that direction.....still scratching my head why the SI does not pre-set the flip&flops correctly ?
sure, I must have missed something...THE THING đ¤Ŧ ....... rest time đˇ
At last some good news:
John’s comments resonated in my memory chip that the problem suspcted to be a logic error was in fact a contact issue under PCB7 đđˇđˇ
the next raod block appeared quickly after fixing the broken cartridge mount with Rudy’s 3D printed spare part.....
testing the finally mostly correct working BG , only one audio channel to be heard đ¤Ŧđ¤Ŧđ¤Ŧ
naturally I feared wrong wiring at the cartridge mount, .....no, all good....at the end it was a broken wire in the DIN plug đ¤
new one with gold-plated pins fitted and back in Stereo sound !
the servo fine adjustment is still an issue to overcome but should be sorted soon as well as the return switch still to be looked at.
so, overall a good outcome - big thanks as always for your interest, comments and pointers.
Good news Alf. I have found most problems turn out to be connection problems - bad mating in connectors, bad solder joints or broken wires.
-john