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 John,
I compared some voltage measurements from my working BG4000 with the problem one:
at 0C1 rectifier output for the 6V rail:
not working BG4000 working BG4000
Off 11.4V 11.78V
On 8.41V 9.4V
at 0C2 6V-rail:
Off 6.6V 6.54V
On 6.04V 6V
at 0C4 24V-rail:
Off 23.16V 24.5V
On 22.9V 23.9V
does that really point to a faulty transformer ??
I will take some pics if the measuring-points are not clear ?!
cheers
ALF
Well, I never thought of that while having been so emerged in the problem.....
I wil check those nunbers with the 'good one' and will report back :-)
Cheers
'Still hoping for a NAND-NOR chip fault'
Hello john,
Well, I aborted that exercise as I ran into an absolute measuring mayham - could not get any steady
Signal on both tables.......enough said !
At last I have some great news: I managed to restore all vital functions.
Replaced 1TR10 and 1TR11, the cap reservoir and.........finally after a faint brain-wave plus
Going through the faul-finding flow chart from the SM I replaced 4IC1 and everything came back to life!
I will have to do some minor cosmetic restoration work and after that will have to attend my sick
BG4002 type5503 and the BG8000.........
Don't be surprised to hear from me again.........love a bit of 'expert chat'
Thank you once again - reading through your posts is an inspiration !!!!
Cheers,
Hi ALF,
So was the reservoir capacitor you replaced for +6 VDC power?The 4IC1 NAND device generates the "R" signal which is a factor in almost all of the control board latches. But it isn't on my list of signals I measured on my spreadsheet. I will have to capture that signal state the next time I make those measurements. Good work in finding the fault.John
Hi John,
I decided to replace the complete set of those old grey caps - 6 altogether but stopped short for now
Attacking the main board and the psu board, replacing the old electrolytic caps as the table is in
'working mood' :-)
Off to a lid polishing torture followed by some 'wood work' and a small paint job. Still looking to refit a
Brushed alu strip for the lid - contacted calssic audio in denmark, but no reply!
The local hardware store may have some brushed alu laminate for kitchen kick-boards......
The only thing missing is the B&O 4000 imprint on it - can't have everything, can you ?!
I may upload some pics, once the job has been completed.
hi john,
something I can not explain:
how is it possible the Beogram 4000 works without the 4IC1 chip ???
I left it out and the table works fine - do I reinsert the chip....the old problem ????
as long as it works I am happy
cheers, ALF
4IC1 is needed to generate the "R" signal. The "R" signal is connected to almost all of the NAND logic inputs on the control panel board. I didn't monitor that signal in my testing unfortunately but in looking at the schematics, the way I believe it works is "R" should be a logic high value when the tonearm motor is stopped and when playing a record. That allows the tonearm to be lowered (when the other accompanying signals are also in the correct state). The control board logic that generates and latches Ǭ₁ (the signal that raises/lowers the tonearm) has several control signals that can take the tonearm out of the lowered position. Obviously Stop, Fast Forward, Fast Reverse will signal the control board logic to raise the arm. Other events would be Slow Forward and Slow Reverse. That is where I believe "R" comes into the picture.
The "R" signal can be activated by FO (slow forward) and RE (slow reverse). What I think "R" does is to allow the Beogram logic to sense a slow forward or reverse command and raise the tonearm for those events.
So I would not leave it out. Without it you lose an important protection piece of the control logic. That wouldn't be good.
Since this appears to relate to one of your original problems, maybe there is an issue with the slow forward and slow reverse settings on your Beogram. Check them with the adjustment procedure for "Adjustment of Slow Slide Transport" (section 4-7 of the service manual). If they are out of adjustment that circuit could have been causing invalid "R" signals when it shouldn't. That would disrupt the operation of the tonearm.
John
I think this is a better picture. This shows the FF and FR switches with the circuit diagram. The default, non-pressed FF and FR buttons have ground applied to FO and FE while FF and FR are open circuit. This results in signal "R" being a logic high as well as FF and FR at control logic latches in the control panel board. Those states allow the tonearm to be lowered when the appropriate commands are generated by other logic.When the FF or FR switches are slightly depressed, for the slow forward or slow reverse commands, the FO and FE signals are then in an open state and the signals from the two trim pot 1VR5 (FO) or 1VR6 (FE) drive the signal "R" control logic. The 4IC1 device needs to interpret that condition as a forward or reverse command and drive signal "R" to a logic low so the raise tonearm signal is generated.When the FF or FR switches are depressed all of the way, those signals apply ground to the FF or FR inputs on the control board logic to raise the tonearm.
Since your other problem went away with 4IC1 removed I would now say that there is a problem with either 4IC1, 4D1, 4D2 or the wiring between those. Something in there is causing problems with the signal "R" generation.
Very tricky: I did try 5 different 4IC1 chips......all with the same result: not good ! And may I assume they can't all be faulty ?!
I also checked those 2 diodes: both are good !
I noticed when I tried to adjust the FO trimmer, the carriage began to very slowly move once the desired
Voltage as per SM was on - it only stopped once the trimmer was set outside the desired voltage ?????
Do we have a dodgy trimmer pot ??
Whatever it may be, I am aware something is not how it should be however the table performs faultless
(So far) with the 4IC1 chip..........
not all of 4IC1 inputs are actually connected to something else and seem just ''blind'' ?
In a quiet moment I shall revisit the case
Thank you kindly for your involvement and all your patience and support :-)
Those typos......
It should of course read ' ......performs faultless without the 4IC1 chip....'
ALF: Those typos...... It should of course read ' ......performs faultless without the 4IC1 chip....'
Only two of the 4IC1 chip NAND devices are used in the circuit. With the chip removed you will be missing the control over the signal to raise the tonearm when you attempt slow forward and slow reverse. John
When your Beogram is "On" and the tonearm is up (platter spinning but no record is playing), what voltage do you measure at FO and FE (the slow forward and slow reverse signals)?They should both measure 0 V at that point because the FF and FR switches are at their normal position and ground is applied to FO and FE.
Next, try and measure FO and FE when the FF and FR switches are in the slow movement position. It is a little tricky to do this as there isn't much space to hold the switch in the slow move position.Last...measure FO and FE when FF and FR switches are fully depressed.John
Where exactly do you want me to measure ? On PCB 3 & 4 of the control panel or on PCB1 ??
May I assume you are talking about RE. and not FE ??
As said previously, I am aware there is a bug somewhere, however if omitting 4IC1 only results in
Not safely engaging slow forward/reverse with the arm lowered I have to say this would be a rare
Scenario, wouldn't it ?!
Jumping tracks on a record I would engage the arm-lift first and even if only pressing FF or FR it is much more likely to engage the fast-forward/return than very gently trying to find that 'slow' position???
I am however curious and happy to measure those points as suggested by you - just want to make sure
I am choosing the correct ones.
Please advise - thank you kindly once again :-)
Cheers - ALF
Hi Alf,Yes I meant RE. Can you put a probe on the non-ground side of 1VR5 (FO) and 1VR6 (RE)?If the Beogram is going to be your own turntable and you know the problem is there then I suppose leaving 4IC1 out would work but I would encourage you to continue on and find the source of the problem. With 4IC1 in the circuit and the Beogram in the mode of "On" with the arm raised, you should see 0 V on FO and RE resulting in the generated signal "R" being a logic high voltage. If that is not the case then you will need to check power and ground to that 4IC1 chip. I think you have isolated the problem to that board if removing it allows everything else to work properly. Maybe there is a problem with a solder joint or trace on that board.
With the table 'on', arm raised, platter spinning, 4IC1 in the circuit I measured:
FR about 25mV, FO about 120mV
I can activate the the 'slow reverse' but the 'slow forward' is not working !!
Again I want to raise the question about that FO trimmer pot ?!?! Adjusting that trimmer leads to
The carriage slowly moving forward without pressing any keys until I readjust to stop it from doing
That ?!?
I los some soldering eyes when I put in a socket for 4IC1, but all of these are not connected to any track
Anyway ?!
do I have to get 6V at 4IC1 pin7 ??
Hi Alf,
FO and RE need to be 0 V when the FF and FR switches are in their normal position as the rest position of the switches apply ground to FO and RE.
Yes, the 4IC1 NAND IC (FCH131) requires power applied. That is positive voltage at pin 7 (+6 VDC) and ground at pin 14. Definitely verify that is the case.If those voltages are there then you should have some logic high voltage for signal "R" (junction of 4D1, 4D2 and 4R1) on the little board with 4IC1.If that initial state (turntable "On", platter spinning, tonearm up) doesn't have a logic high (somewhere between 2 and 6 volts), then something is wrong.Have you checked the voltage on both sides of 4R1 (12K Ohms resistor)? It should be around +6 VDC on the side connected to the +6 VDC power bus and somewhere between 2 and 6 VDC on the side that is signal "R".
To restate the 4IC1 connections necessary:FO goes to 4IC1-3RE goes to 4IC1-10The output of FO through the NAND gate comes out 4IC1-8 (and goes to 4D1)The output of RE through the NAND gate comes out 4IC1-1 (and goes to 4D2)4IC1-7 goes to the +6 VDC power bus4IC1-14 goes to ground
The anode sided of 4D1 and 4D2 connect together with 4R1 (12K Ohms resistor) and is the "R" signal.John
keeping busy :-)) here is an update:
I measured 4IC1 Pin7 (Vcc) against Pin14 (ground) I get about 6.14VDC
both sides of 4R1 deliver the same voltage.
measuring FR at the trimmer 1VR6 against Pin14 (ground of 4IC1) I get 11mv
measuring FO at the other trimmer 1VR5 against Pin14 I get 2.3V !!!!
cheers - ALF
Once again - it obviously depends on how and where you measure ........
The pic attached shows the two points on Board 1: FO and RE of the trimmers 1VR5 and 1VR6.
If I measure on these points against the groud of 4IC1 Pin14 I am getting different results, showing
FO around 10mV and RE 0.5mV - that paints a totally different picture !
I wonder if these are the measuring-points you referred to ?!!
ALF: Hi John, keeping busy :-)) here is an update: I measured 4IC1 Pin7 (Vcc) against Pin14 (ground) I get about 6.14VDC both sides of 4R1 deliver the same voltage. measuring FR at the trimmer 1VR6 against Pin14 (ground of 4IC1) I get 11mv measuring FO at the other trimmer 1VR5 against Pin14 I get 2.3V !!!! cheers - ALF
10 - 11 mv is close enough to mean the switch is grounding the signal.The important thing is that you only see 2.3 VDC on the 1VR5 and 1VR6 trimmers when the FF or FR switches are depressed (slightly or full). Is that the case?If you read 2.3 VDC on 1VR5 or 1VR6 when the switches are not depressed then something is wrong (maybe the rest state of the switch doesn't have a good ground).
You need to be measuring signal "R" during these tests as well though. Verify that "R" is 2.3 V or above when the FF and FR switches are not depressed and verify that "R" is well below 2.3 V (maybe 0.5 V) when FF or FR are depressed.
As said in my previous reply it depends at which point exactly I suppose to measure 1VR5 & 6 ??
Again I will attach a pic - sorry, but it is the smallest size available on the tablet - to shiw at which points I measured 0.5mV and 11mV.
The match-heads point at it.
Hi john,
With the arm raised, platter spinning and 4IC1 fitted I measured ' R' on PCB3 against ground of 4IC1
Forward/reverse switches not depressed: R = 0.710V
Forward depressed: R = 0.706V
Reverse depressed: R = 0.4mV
The only function I am unable to get to work is the 'slow forward' - 4IC1 fitted or omitted!
Cheers ALF
Okay, thanks for those measurements Alf. It is difficult to troubleshoot problems without actually being there so that confirms for me that control of "R" is your issue.The problem looks suspiciously like a problem with either the FF or FR switch. Earlier in your restoration did you remove those metal switches and clean them? They also need to be checked that they are straight. I would run some tests with the top of the control panel opened up so you can manually observe the leaf of the switches touching the contacts. The FF and FR switches are different from all the other control switches because they need to be touching the contact for ground in their rest position. I suspect one of yours is not so it is always sending the non-ground state to 4IC1 which prevents "R" from going to 2+ Volts. Either the switch itself or the wiring/connection from the switch.With power off the Beogram, measure the resistance between the 1VR5 and ground and 1VR6 and ground. The switches should be putting a ground there in that state so you should measure close to zero ohms. With 4IC1 removed, there is nothing to switch the "R" signal low so you should always measure a high (some value over 2 V) because there is a 12K ohm pull up to +6 V there. Earlier you said the Beogram functions perfectly (in all other functions) with 4IC1 removed so that would be why..."R" is always in the high state which allows the other control signals to work.
While you have 4IC1 removed, what voltages do you get for F0 (1VR5 to ground)? You should see close to zero volts when FF is not depressed and around 2V when FF is depressed. Also measure the voltages at RE (1VR6 to ground) to compare to.John
Some new measurements:
RE
Not depressed = 0.5mV
Depressed = 2.4V
FO
Not depressed = 15.4mV
Depressed = 15.6mV
Remember, the slow-forward can not be engaged !!
I checked the brass-tongue and contacts of those two switches again - the tongue sits right between
The lower and upper contact point in both switches but only RE -slow reverse- works !
Everything is straight - I had the top of the control-panel off and had a good look at the tracks towards
4IC1 again - no suspects.
With the power off I checked the resistance from 1VR5 and 1VR6 tto ground.
Depending on the point of measure - see my matchhead picture - VR6 showed 0.4/0.9 Ohm
VR5 showed 680/0.4 Ohm.
Whatever that reveals I will replace these two timmer pots and let the matter rest.
I fully understand the problem with the long-distance analysis and most certainly appreciate your time
And effort - it looks as this is a far as it goes in terms of success given the circumstances.
A non-working slow-forward is the least of my worries as long as everything else is working :-):-):-)
Some users with very little fine-motor-skills may find that feature difficult to execute anyway ?!!
Hi Alf,It appears your problem has changed as you have worked on it. Originally I understood the problem with the Beogram was the arm would not lower. If the generated signal "R" from the FO and RE signals (through the 4IC1 NAND gates) was low (less than a volt), then "R" would prevent Ǭ₁ from latching low which would not allow the arm to lower.From there, you ended up removing 4IC1 and then Ǭ₁ was allowed to work and the arm lowers. To me, that means the problem is isolated to the circuit involving generating the "R" signal. With 4IC1 in circuit, FO and RE have to both be a logic low (less than a volt) for "R" to remain high (something over 2 V). With 4IC1 out of circuit, there is only a 12K Ohm pullup to +6 V there at "R" so it will always be logic high and a non-factor in generating Ǭ₁. So the tonearm function should work...which you say it does in this case.Now with your ground measurements - From you picture it appears you are measuring FO and RE across their respective trim pots. One side of each trim pot is ground. So when FF and FR switches are at rest, you should measure continuity between FO and RE to ground. If you don't, you have a bad connection or solder joint somewhere. When FF is at rest FO should be grounded so you shouldn't see 680 ohms there (when the Beogram is unplugged). You are right there at the heart of the problem. John
ALF: I checked the brass-tongue and contacts of those two switches again - the tongue sits right between The lower and upper contact point in both switches but only RE -slow reverse- works !
sorry if that came across the wrong way:
the brass-tongue is NOT between lower and upper contact point when FF is at rest !
for both, forward and reverse it only is between points when the 'slow' functions are pressed, meaning not fully depressed !
as for the other issue with the trimmers:
I do not fully trust 1VR5, hence the replacements of 1VR5 and 1VR6.
lets see what happens......
Okay, good. However, that gets back to the original issue with the Beogram tonearm not able to lower with 4IC1 in the circuit.Either FO or RE is causing "R" to drive low which prevents Ǭ₁ from latching low (for the tonearm drop command).Even if the trimmers are bad, at the start of play, FF and FR are not pressed so FO and RE should have a good ground applied to the 4IC1 inputs which keeps "R" at a logic high. Since "R" is not doing that and is at a logic low, something must be wrong with that ground signal from the switch. The reason I think that is because with 4IC1 out of the circuit, "R" stays high ( > 2 V) via the +6 V pull up so that part of the circuit works.If the ground signals are okay and 4IC1 is the problem then it would be suspect (but I think you said you have replaced that) or the power and ground to 4IC1 is suspect.John
I have all but given up on fixing that problem........and accept the fact the table basically works with one
Tiny exception:-)
You were of course right in not suspecting a bad trimmer - I replaced it but the problem still remains.
Yes, I have 5 new FCH131 chips and tried each of them in 4IC1 position...no change !
It may well be a gone-bad wire-connection somewhere or a dry joint - having said this, I have now spent so many hours on this and just want to move on - there are other 'patients' waiting. .......
I said this before, if your fine-motor-function and touch-feel are not up to scratch you will find these
'Slow-function' tricky anyway - I can't even remember when/if I used one intentionally ?!?!?
I learnt something thanks to your patience and that in itself I regard as a positiv outcome.......
Off to my sick BG8000...........