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,
It's been a long time and my sick BG4002-5503 has had a good rest sinc the last work.
I wanted to resume battle as I am quietly confident the problem will have an easy solution ?!?!
In the meantime I installed a 'proper' 240VAC transformer and hopes are up......
The fault-finding chart in the SM talks about a 'pulse generator', meaning the circuit that involves the opto-resistor/bulb separarated by the position-marker ?????
Sadly the problem is still present:
Pressing 'ON' the platter spins, starting at 33rpm for a second and changing quickly to 45rpm way before it should change, while the carriage
Is moving across, arm raised all the way, triggers ES and returns to its resting position.
With the record on it does exactly the same, without arm lowering..........
One side observation though, the solanoid could be operated freely without the bulb supplying the opto-resistor ?! Any other time it won't engage!
Would you have any other/new suggestions ??? At the moment it is shrouded in mystery while I am still convinced of a rather simple solution!!
kind regards
ALF
So the table seems to have two problems:
Sudden speed-change after 1sec from the start 33 to 45
Arm does not lower at 30cm position with record on
Hi Alf,These problems always seem like a simple fix after the fact . Determining what to fix is the problem. It is nearly impossible to trouble-shoot without actually seeing the unit and making measurements. Going on your described symptoms I can only venture to guess the problem is with the analog control system logic interpreting the sensors. If any components in that control system start to go bad the result will be unpredictable behavior. Beolover had a strange control problem on a Beogram 4002 he repaired this year. The circuitry involved in that Beogram is different than yours but is similar in that it is a similar analog control design. Since we know the Beogram starts at 33 RPM and but can change to 45 RPM only through manual depressing of the 45 button or the auto-speed change control circuit, your problem has to be in the components of that control circuit. The service manual shows that circuit involves 1TR2, 1R5, 1C3, 1D5, 1C24 to 1TR23 (plus some other surrounding components). The first suggestion is to monitor, with an oscilloscope, the junction of 1R5, 1D5 and 1C3 to watch what happens when the turntable starts up. That signal should be at zero volts unless it gets a signal from the analog control circuit to drop to about -1.5V for about a second. That toggles and latches the speed control to 45 RPM. Either a hard signal is occurring to cause that event or some part of the control circuit is unstable and generating that signal. If you can catch that undesirable event on your scope you should be able to trace it to its source. The actual 45 RPM automatic speed change control signal is shown in the middle of the Beogram 4002 schematic as a series of negative going pulses between 1D5 and 1C24...generated from the circuitry associated with 4IL1 and 1TR23. Something in that area is most likely causing your failure. Since the same circuitry is involved in the automatic arm lowering control, the problems could be related.
You can see why a problem developing similar to what Beolover encountered in the similar BG4002 Type 5524 control circuit could cause problems like you are seeing. If a transistor is not turning on (or off) correctly the control circuit misbehaves. -sonavor
Hi john,
Apologies for the late response........you may or my not recall an earlier question in regards to the LDR 4R1 ??
I presume he is part of the 'pulse generator' circuit ?!
Well, apart from a burnt-out bulb in that circuit I had to discover that 4R1, which is a RPY58 LDR........almost impossible for find, is mal-functioning , or should I say not functioning at all
Meaning, most if not all other checks are pointless until I have found a working replacement ?! I did suspect something odd going on there for some time as the Position-maker did not cause any signal change.........!
Now I am well and truly stuck.....nice.
Naturally there are plenty LDR's available but nothing that matches the spec of RPY58
If you happen to have spare one for sale I would be delighted, if not the waiting game is on for a cheap donor unit.
Cheers - wish I would gave better news
ALFA
How to turn typos into $$$ ?????
ALF: Well, apart from a burnt-out bulb in that circuit I had to discover that 4R1, which is a RPY58 LDR........almost impossible for find, is mal-functioning , or should I say not functioning at all Meaning, most if not all other checks are pointless until I have found a working replacement ?! I did suspect something odd going on there for some time as the Position-maker did not cause any signal change.........! Now I am well and truly stuck.....nice. Naturally there are plenty LDR's available but nothing that matches the spec of RPY58
I don't know if this ended up as a viable solution but this discussion about replacing the RPY58 in a Beogram 4002 & 6000 is in the Beoworld Archived Thread. Both Beoworld members tournedos (Mika) and yachadm are still contributing to Beoworld so you could send a PM to them about the results of that thread.-sonavor
Yes, thanks I did follow that link/discussion but am unaware whether or not the outcome delivered a solution ??
On a more promising note: a strike of luck delivered me a couple of those elusive LDRs from the UK.
Awaiting their delivery now and will get back to my sick BG4002-5503 as soon as.......
Perhaps the solution ?
Will report the outcome if interested.
Cheers