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! I have a 4002 type 5503. The tonearm will suddenly lift then drop back during play.
It will do it usually once while playing a 33 and can do it any time. It is just a momentary lift then right back down without any input from me.
I have one other issue that is it wants to set down way before it reaches edge of the record.
Other than those two things it performs great.
Thank you for any help.
Hi, I haven't encountered that kind of failure yet but I would have to suspect an electronic problem rather than mechanical. You will need to dig out the service manual and check the circuit involved. On the adjustments for the set down point, section 4-3 of the service manual shows that adjustment procedure. If you don't have a service manual you can get a PDF version of it with silver level membership on Beoworld.-sonavor
Thinking more about your problem with the arm in the lowered position, then raising and lowering again...I wonder if the problem could be with an unstable solenoid circuit. On those turntables, when the command to lower the tonearm is made, there is a solenoid that activates to move the mechanical lever to lower the tonearm. After the solenoid is engaged it remains in the activated position via a circuit that holds the solenoid in that state until the raise tonearm signal is received. Perhaps that holding circuit is dropping out, then comes back on its own?Maybe Dillen has seen this type of problem before.-sonavor
Contacts in the up/down switch on the operating panel too close?
martin
Check your main power lines for micro blackouts
Collecting Vintage B&O is not a hobby, its a lifestyle.
Update; Now that I have decided to find the problem and posted this thread it has not lifted during the last 3 lp's I have played!!.
I did remove the covers and platter and did see that the solenoid has been replaced as it had the plastic arm that liked to smoke them. I also see a lot of hand soldering from the factory that looks cold. So I think I will re-solder the solenoid and maybe the dull looking connections to see what happens.
Thanks for all of your replies.
In resoldering I would just apply some new flux and touch up the existing solder joints. Don't just reheat the existing solder joints without flux. You may have already planned to do it that way but I thought I would mention it anyway.-sonavor
Last update. I re-solderd the solenoid leads and it has not lifted while playing. Now playing like it was new!!
Thanks for all the help.
Well my problem is still there! After re soldering lots of connections and checking everything I know, I'm stumped. As I said the problem is very intermittent and lasts for only 1 to 3 seconds then nothing or up to 3 records then it will happen twice in the next.
What I have done, re solder connections, re cap every board, spent hours watching my scope to see what is happening and this is what I have found.
Solenoid Circuit starting with 1Tr14- no change at the base, collector rises to .81. 1TR15- base goes to .31, collector goes to 17! (checked many times) 1TR16ends up with 17 volts at base, emitter & collector (I replaced 16 with no help), 0TR4 ends up 17 volts at the base but shuts off?
As the problem only lasts 1 to 3 seconds it's hard to get measurements. My volt meter is too slow to get a full reading so I use my scope to check and I'm lucky it has a memory to look at.
The other thing I have noticed during this is at the base of 1TR15 during normal operation it looks like a high frequency oscillation and when the problem hits it goes away.
What gets me is that with 17 volts at the base of 0TR4 it should be turned on but the solenoid shuts off like it"s turned off!
I have checked all ground connections and found 1 bad one for the optics in the tone arm but no help there.
Any help is greatly appreciated.
Jim.
Normally I would offer to hook up a working Beogram and check my voltages for something to compare yours to... but I am afraid I won't be able to do that for a few weeks as I am swamped with projects I am currently in the middle of. If you can post a diagram of the circuit you are measuring and monitoring it might help someone on the forum come up with some other things to try. -sonavor
Regarding random lifting of the tonearm, I had this exact problem on a Beogram 6000 Quad.
I suspect that the rubber band that drives the threaded bar is loose. (Servo motor drive belt)
I suggest that you invest in a replacement belt set from Dillen.
Regarding the set down position, this is adjusted by moving the ruler slightly, using the adjustment screws in the oval holes.
Regards Graham
Sonovar, I will scan a copy of the circuit to upload when I go back to work on Tuesday.
Graham, When I am testing the platter is off and the tone arm is down but just sitting in space so the servo motor is not running. Also the set down issue is fixed.
Thanks, Jim.
Here is a schematic for the circuit. The components are 1TR 14, 15, 16 & 0TR 4. Any help is greatly appreciated.
Sonavor, I have been back at my 4002 and this is what has happened. First it has sat for a couple of weeks to get some other things done. I put it on the bench set up my scope and hit on. The tonearm went over, set down and almost immediately picked up and set down! It happened so fast I did not get a single measurement. I turned on the scope's save function and of course it would not do it again the rest of the day.
I think it is a ground problem as the voltage all around TR 16 goes so high as if it is shorted. I have replaced it but no luck. I have jumped the board ground to the power supply caps but it still did it. Now I have a jumper from the bottom of R57off the emitter of TR 16 to see what happens.
I have never had a semiconductor have a intermittent problem like this they have always been bad or good. But you never know. I just wish it would break so I can find it!!!!
One other question. I have never seen a resistor like the one for the emitter of 0TR 4. The one that gets switched into the circuit when the tonearm goes down. It has 2 leads on each end and one from each end are soldered together. Do you know what this is about?
Thanks, Jim
Jim Carr: One other question. I have never seen a resistor like the one for the emitter of 0TR 4. The one that gets switched into the circuit when the tonearm goes down. It has 2 leads on each end and one from each end are soldered together. Do you know what this is about?
There is a description of that for the Beogram 4000 on my Beogram 400x thread. I haven't ever done any measurements on a 4002 regarding this functionality because I haven't had any problems there yet. However, the functionality should be pretty similar. What happens is the solenoid is instructed to activate with full power applied. Within several milliseconds of that event, the load resistor is switched in to reduce the current through the solenoid. It should end up at a value that is enough to hold the solenoid (in the tonearm down state) but not draw as much current as when it first engages. Maybe there is a problem with that switch. See if you can take a picture or two of the switch.
-sonavor
One more thing. Read about my solenoid measurement carefully. Always unplug the Beogram with adjusting and setting up the scope probes. It is easy to want and setup and get to the measurements quickly. You can short something out that way...don't ask how I know that.
I am familiar with the solenoid circuit as I had to replace the original levers on the 4002 as they were plastic and would crack then the solenoid would go up in smoke! We had customers come in horror when they would see the smoke coming out of their brand new decks! I replaced the one in mine for the first owner back in 75 and never had to work on it again until now.
I have checked that part of the circuit and everything seems good. I think the problem starts around TR 16 as that is where the voltages go off.
If you are confident that the solenoid is good then that leaves the control circuit which does involve 1TR16. 1TR15 and 1TR16 control turning 0TR4. They are controlled by 1TR14. I would monitor the base of 1TR15 next. Set the scope to read the "tonearm down" level which the schematic shows to be around 0.5 VDC. So you will need to verify what the up and down levels are. If you can get the down level set you should be able to put your scope in single mode and the trigger to go on a voltage rise. Also set it so the scope records some time prior to the trigger so you can catch the whole event. That should give you a reading of an unwanted "tonearm up" signal there if that is what is occurring. Test your set up with a real command from the Beogram control panel.
There are several Beogram things that feed into 1TR14 which can signal the tonearm circuit to lift. So the actual problem could still be elsewhere than 1TR15 and 1TR16. Monitoring and catching the event at the base of 1TR15 will tell you for sure that it is an unwanted lift signal coming in (rather than some instability of the lift circuit). Another place to monitor for an event is node between 1D19 and 1R51.
Another test you can do to check the tonearm lift is to remove the belt and platter completely. Let the tonearm lower (to an invisible platter) and gently tap the tonearm to watch the tonearm motor move it forward. See if you can get the unwanted lift to occur that way so you can find a convenient method of measuring with your scope.-sonavor
I have checked all of those points which took weeks to do and here is what I get.
Starting with the base of TR 14 no change at all. The base of TR 15 drops from .5 to .3 (it's already in cutoff so it does nothing) The collector of TR 15 & base of TR 16 goes from 4.7 to 17 Volts! As well as the Emitter and collector of TR 16 (as if it is shorted) As the emitter of 16 is tied to the base of 0TR4 it gets the 17 volts too.
I have checked all the connecting wires for 0TR4, grounds etc. The worst part is it only lasts for 1 to 3 seconds then may not do it again for hours.
I have the platter off so the tonearm is just hanging down. I also have tried hitting every switch, touched the tonearm, lifted the board up and moved it around, stared at it, threatened it, offered it new vinyl, nothing seems to make it happen it just does when it wants too.
With the voltages I see around TR 16 and that nothing happens at the base of TR 14 I do not think it is from any switches or sensors. I also disconnected the ground wire for the tonearm optics and that does not make the arm lift but will keep it from lowering.
I have a few points to monitor today and hope it shows something. Ill keep you posted.
Well the problem has not shown itself for weeks now. I finally put the covers back on and I am just playing it. I do have 1 question, where can I get a new belt? I bought one from Vintage Electronics and it seems too tight. It measures 16.75 in when laid flat and I think they should be 17 in.
Get one from Dillen on this forum he has the right ones
Well, not quite there yet with this one, but working on it.
Martin
Please let me know when you have them!!
Well I'm still at it. My deck worked just fine for about 2 months then the problem came back. I have replaced transistors 1TR14, 1TR15 & 1TR16 with no help. Also when I monitor the base of 1TR14 there is no change at all when the problem happens. The base of 1TR15 drops from .5 to .3 mv. so I do not think that is the cause.The base and emitter of 1TR16 goes to 17 volts as does the base of 0TR4 but the tone arm solenoid activates and lifts the arm which I do not understand.
The other weird thing is at the base of 1TR15 I see a 10mgz signal that I do not think should be there although it's there while the deck is working fine and goes away when the problem hits. I am attaching a picture so maybe someone out there that has a 4002 can look at theirs and see if they have it too.
Well it looks like I have found the problem!!! An intermittent open base-emitter junction on 0TR4!. It's only taken 2 years but It's working great now. It finally went out long enough to get the readings I needed and was able to test it out of circuit to prove it
Good job!