It seems my Beogram 4004 now does all functions happily except lowering the tone arm (see post "Beogram 4004 Trouble"). Running it with a disk on the platter results in positioning the arm at the beginning of the record after pressing "start" as it should. However, then the voltage drops (or the mains fuse blows) and the current is maxed out (I ran it at 0.7 Amp current limit). The same happens when positioning the arm manually somewhere above the record using "<" and then pressing "up/down". After this happens the only way to reset the deck is to drive the slide back into start position by rotating the threaded rod by hand. After the switch underneath the position indicator is activated by the slide (a click is audible) the current drops to a normal level and the voltage recovers to 25V, and all functions are back.

Suspecting the solenoid, I disconnected plug P4 and measured the resistance across the solenoid. I turned out to be 9.5Ohm. Then I connected my power supply between the brown (#6) and ground (#10) leads of the plug that are connected to the solenoid. Maxing out my power supply, the solenoid drew 1.4 Amp at 14 V due to the current limit. Nothing happened at the solenoid, except that it got a bit warm to the touch. However when pushing the rod within the solenoid a bit with my finger, it finally snapped to lower the arm. I lubricated everything and made sure that things move smoothly, but that did not change anything.

At this point, I started thinking that the solenoid coil really may have a problem. Hence, it would be very helpful to know what the resistance of a properly working solenoid is, and what the normal current at 25V is (it seems that the circuit directly applies the 25V mains voltage to the solenoid through 2IC4 whenever arm lowering is required). And of course, if it is fried, is there a proven solution to this problem??

Thanks much in advance!

Rudy

ok test your solenoid by disconecting the enamled wire(s) that come from the unit itself onto the board in front of it. This will rule out any miss-connections or other shorts in the wiring harness! The solenoid should be about 9R I am sure of it and is very unlikely to be faulty.

The circuit applies about 21v to the solenoid for only a fraction of a second before tr10 starts to regulate the current flowing through the solenoid to a much lower (safe) value by shunting current away from the base of tr9.

C23 delays tr10 tuning on to allow the solenoid to engage at a higher current.

If this circuit is not regulating the current then check all three transistors and the capacitor!

Just to add if the solenoid is pulling too much current this might explain why you can not release properly, as the other circuits will in all likelyhood lock up or behave abnormally, due to a voltage drop.

Hi Olly,

Thanks much for your insight! I was wondering about whether there is only a short pulse or not...I noticed that the mechanism locks in the "arm lowered position" after the solenoid engages. Is it released by a second pulse to let the arm raise back up? I will check the circuit as you suggested and report back! Thanks!

Rudy

Ah ok no the solenoid should not stick when power is removed, if that is what you mean?! I had a beoram perform the same thing which turned out to be the parallelism adjustment of the lower arm but before you check that when you re-lubed things did you partially strip the mechanism down to remove old lubricants? If not, remove upper and lower arms at the pivot points now, clean and relube with sewing oil. I usually strip this part including the damper and give everything a thorough clean!

When you have done that, re-assemble and check that the lower arm is parallel with the pcb below it, when the sol is in the engaged position, the manual explains the proceedure.

When you have done the above, test your sol with your psu again. DO NOT leave the solenoid at this voltage if you want to leave engaged I would reduce the voltage right down to a couple volts, but it should be satisfactory to see the thing pull in and no more. BTW you mention above 1.4A @ 14v this is about what you would expect!

The only thing next is to check the compnents I mentioned above to make sure the circuit automatically reduces the current to the solenoid as with your other symptoms. Maybe exchange the solenoid for a couple of low power automotive lamps in series and see that they dim dramatically, and that you can then disengage the arm by pressing <> etc. that way you will not risk damaging your solenoid.

Hi Olly,

Does this mean there is a high voltage pulse initially to move the arm down, and then the solenoid runs on reduced voltage to stay down? In my case, there is a 'click' when the solenoid is fully engaged, and it stays in place in down position. It stays there when the voltage is turned off. To get it into the "up" position, I have to move it back manually, overcoming an initial slight resistance. After that the arm moves smoothly up, and the solenoid piston goes back into the "up" position. Thanks!

Rudy

Like I said Rudy this is in all likelyhood to do with that parallel adjustment I talked about previously. Check the lever yourself when engaged. I never worked out where it was catching but once I set it up properly the fault completely dissapeared and has not arised since! It was almost as if there was a small holding current or residual magnetic field holding the solenoid in. Please strip and thoroughly clean as above and go through the steps to check all is ok.

I think you are close now..

Oh and yes just an initial pulse followed by a low holding current after xx milliseconds.

O.k.!!! I finally figured out what the problem was (thanks again, Olly, for your enlightening insights!): The insulation washer for screwing 1IC4 down to the heat sink pad was installed upside down (that much for buying from unknown sources on ebay!), which prevented it from keeping the screw from touching the collector/heat sink of the transistor. This created a current path to the chassis, resulting in a short circuit whenever the solenoid circuit was engaged.

I noticed the issue while following the short circuit current path, when I realized that floating the electronics by pulling plug P9 on the "8" board, which connects the system to ground (and the pickup to the DIN output cable) made everything work smoothly. However, I measured 1.5-3V (depending on the stage of the solenoid motion) between PCB ground and the chassis, so there had to be a short between the solenoid circuit and the chassis. From there it was easy.

Excellent, so is everything working now?

I think all mechanical functions are now there. I have not had a chance to put the platter back in and try playing a record to see if it tracks o.k....and then there is the "dented" cartridge it arrived with (the rpm panel came loose during transport and hit it). The needle seems to look o.k....we will see...would you buy a used cartridge or go for a Soundsmith replacement?

Rudy

Final conclusion: Once I put in a different cartridge (the dented one is dead) it played a record very nicely. Tracking seems o.k. (at least as far as I can tell...this is my first 4004...). However, I realized the output relay did not work. After contact spraying and a very slight sanding of the contacts this was remedied, too, and it seems full functionality has been achieved. Now on to the cosmetics!

Very good job indeed, its always difficault to find failures when "know it alls" has tried to repair, I had a BG 6500 where a Mex. specialist had tried his tricks, result: Jumper leads, connected solder points, bad solder points and broken PCB tracks, some people dont understand that these wunderful pieces needs love and care when repairing.