After diagnosing and repairing the longstanding  issue of too slow 45rpm speed* I reassembled the 4002 and was confronted with yet another problem - hopefully this will be the last bugbear. All functions work. All illumination works. I have correct speeds whatever I select. The platter is level and the sensor arm is the correct 23mm above the alu area of the platter. After installing the refurbished main pcb done by Menahem, I played the turntable for a couple of weeks without any problem and now this...

After pressing "Start", the arm moves to the lead-in record groove, the arm drops correctly and then starts traversing very rapidly across the record, dragging the poor cartridge up to the leadout grooves. The arm then lifts, returns to rest and the turntable switches off.

Please help once more, gents Where can I start looking for the cause of this problem?

*) I am a bit hesitant to offer cures for platter speed issues as I know almost nothing about electronics but here goes, anyways. After receiving graciously given advice here (including from Menahem) to clean the contacts of the Siemens relay, the problem was finally traced a few days ago to the fine trim 1kOhm linear pot situated above the control panel. I did of course clean the relay contacts but this did not cure the problem so I had to look elsewhere. 

I desoldered the part and removed the worm driven wiper inside and immediately saw the problem. The wiper showed signs of arcing and the carbon track had corroded or broken up near the contact pins.

I had a vial of Leitsilber L100 conducting silver lacquer and painted the area around the two pins, thus reconnecting the contact pins once more with the carbon track inside.

After assembling all the parts, I soldered-in the pot, pressed 45rpm and all is well. For anyone here interested in trying this kind of linear trimpot repair, the procedure is not too difficult. The wormdrive and wiper inside is held in place by a split wedge on the left of the plastic housing. I made a little 'pry' from 3mm stainless wire to remove the wedge. The tool looks like a flat blade screwdriver bent into a hook.

The same tool can also be used to lift the top platter, btw.

Cheers

andre/dauphine  

Sounds like something in the tracking circuit went wrong.
Either the lamp/sensor/interrupter (loose on the spindle ?) assy at the foot of
the carriage or some electronics on the main board related to the tracking.

The fingerwheel trimmers losing contact is a wellknown problem. Well done !

Martin

Hello Martin

Thanks once more

I'll have another look and see what I can find.

Will advise asap.

Regards

andre/dauphine

Hello

This is what I found and will replace them tomorrow. Hope renewing these will cure the problem. The clamp holding the slotted plate around the arm base is tight and the area around there is clean.

Regards

andre/dauphine 

What is it, you would like to replace on that board ?
I suggest you check the tracking circuit and related mech. as mentioned above.

Martin

Hi Martin

Both of the parts on the underside of the board shown above have signs of 'bubbling'. I take it then these have nothing to do with the arm dragging problem? I will have to re-study the manual and familiarise myself with the tracking circuit.

Regards

andre/dauphine

I wouldn't worry too much about anything on that board.
I suggest you check the tracking circuit and related mech. as mentioned earlier.
It drags towards the left because it is fed a wrong signal from the tracking sensor, either
the interrupter has become lose from the tonearm base spindle, something went wrong with
the sensor or lamp assembly or the electronics are somehow misbehaving.
The tracking electronics are on the main board.

Martin

Hi Martin

I really appreciate the advice and clues as to where to look. I got the same advice about the board I showed in the pic from a friend more qualified than I am.  He advised those little bubbles on the 2 caps are just wax - nothing to worry about.

The present symptoms are dragging of the arm to the left and the tonearm traversing much too fast.

I had to take a short break but will return to the problem this evening and tomorrow.

I already had a thorough look at the interrupter which is held with a clamp to the arm base spindle? and everything is tight and clean there.

The cover plates are still off so I think I will take a close look at the main board incase I see a broken track or anything else under a 60X stereoscope I have.

The sensor arm's lamp is OK and I've got Menahem's LED + resistor installed inside the black cover. That also worked after installation and there's another UV? LED-like device with bent wires somewhere around this area which I'm not sure how to test.

I understand one can photograph it in the dark with a digital camera to see if it is emitting light, which I will also check this evening.

What is so strange about this problem is that absolutely everything except the 45rpm speed worked fine for weeks after I installed the main board after getting it back from Menahem. 

I'll post here if I have news.

Regards & a fine weekend.

andre/dauphine 

Ambient light may confuse the sensor (at least the original sensor - I am not sure what is in there now).
Have you tried with all surface panels fitted ?

Martin

Hi Martin

Thanks, I know about ambient. The plates at one stage was completely fitted and the problem still showed up. Initial tests after fixing the 45rpm speed was done with the covers fitted. I was working in my workshop and with bright  fluorescent directly above. I also had a 100W worklamp above which I switched off as soon as I saw what was happening.

During the weeks I played without problems, the plates were first just loose on top, then fitted properly and the light above were from  5 40W incandescent lamps. At this time, the platter was still not properly level and flush with the plates.

So after the 3 weeks or so while I 'rested' before tackling the 45rpm speed problem, all worked OK, despite the platter dipping slightly at 12 o'clock.

The other change I made was to insert the coil of brass shimstock and changed to another lubricant in the spindle bearing.

Therefore, 3 parameters changed. The 45rpm speed got restored, the platter is now perfectly level and flush with the top plates and, the bearing hole has been shimmed.

There must undeniably be a little more spindle bearing friction because of the shim. With the belt and top platter off, I can still spin the platter with a finger flick although I had to make small + adjustments to the speed pots.

After receiving your earlier comment about the original spindle bearing tolerance where I could move the platter say at 3 o'clock and 9 o'clock and observed (perhaps wrongly) excessive bearing sideplay as compared to my other turntables (Micro, Micro Seiki and Garrard 301's) - I think I will also remove the shim incase this could be causing a problem.

Except for the 45rpm repair, I think I will restore all revised settings to as close as possible to what it was when everything worked.

And of course look and double-check all the other possibilities you mentioned.

I'll let you know what I find.

Regards

andre/dauphine

Hello Gents

I am still troubleshooting the arm dragging problem and have been delving deeper into the heart of the 4002. I have removed this lamp? and found it and the surrounding area drenched in sewing machine oil. My fault as I am unused to lubricating turntables with Elna oil which is almost as thin as water (the dispenser belongs to my wife and she cut the nozzle far too much)! and the stuff ran everywhere it shouldn't have

I have just cleaned-up the mess and vacuumed and used compressed air to get the stuff out of the black box in the pic.

Is there any way I can test the lamp to see if it still works?

Regards

andre/dauphine

Put an ohmmeter across its leads and check for continuity.

Martin

Hi Martin

Thanks

I've just checked. No continuity I will have to check the two scrap decks for a replacement.

Regards

andre/dauphine

Lamps can blow and break for any reason, even from mere vibrations but with another lamp fitted
I suggest you check the voltage across the lamp, just to make sure it didn't blow
from overvoltage.

Martin

Hi Martin,

Thank you. I found these from the scrap decks. The lefthand lamps in each are still OK so I will use one of these. There could have been a bit of vibration or shocks over the months I worked on the 4002 as I used a very small plastic mallet on occasion to tap some of the top plates into position. I will avoid this from now. 

I will also check the voltage which I think should be between 21.5 and 24Vdc.

Regards

andre/dauphine

Your pictures show the light sensors not a lamp! The two above belong to a gram4000.

Also a blown bulb should not result in a the sled responding as you suggest, and oil should not conduct BUT if there was enough it could have acted as a light gathering lens in front of the sensor or something equally strange!

Put everything carefully and meticulously back and test again then if problems still persist start some proper troubleshooting or you will cause far more serious problems in my opinion!

What I would do in your position - remove platter, disconnect shutter lamp (the glass bit above the sensors), press start let arm go to play then see if the problem persists if not reconnect bulb and go from there, if it does disconnect sensor etc...

Correct.
Those are the sensors. (The ones with four leads will track both ways!).
The lamp is a wedge socket type and should be very easy to replace.
It sits right above the interrupter (where the sensors sit below).

I often find a little oil around the screws holding the assembly and also between the
two plastic halfes. Nothing to worry about, unless it's really soaked.

Martin

Hi,

A couple of innocent questions:

1) are both arms parallel and at right angles to the deck?

2) how long does the pickup arm take to lower?

It seems to me that a bad sensor lamp would just bring the pickup arm close to the sensor arm and skip the same groove over and over again...

I am sure that this problem is a badly adjusted paddle and or detector at the base of the carriage tube.

It does not need to be far out for the arm to travel continuosly inward once the stylus hits the record.

Hello Gents

I'm sorry I missed all your valuable posts (it seems my auto notification got switched-off).

Yes, I'm still busy troubleshooting and must admit I'm getting a bit depressed about the situation as more symptoms are manifesting - the arm no longer returns, let alone drag the needle across the record etc. The keypad has all new switches and tests perfectly on all 7 controls out of the turntable etc and so on.

Anyway, I'm now looking at the possibility of non-functioning sensors. Menahem's LED + 1KOhm resistor mod works as the turntable operated perfectly with it. Although I don't suspect any of the sensor devices to be faulty, I must find ways to test to see if they work. The paddle (is that the slotted plate?) and the sensor device below - how would one test this?

I have already removed this device from the turntable and tested for continuity but this must have been an incorrect test. Instead, if my multimeter is set to Ohms and one touches the two leads, there is a resistance reading. If one shields the lamp? from light, the resistance reading changes.

The 3 other similar devices I retrieved from the scrap 4000's behave exactly the same. Can I therefore assume this sensor can be eliminated from troubleshooting?

Next, earlier this evening, I switched off all lighting in my workshop and photographed a LED-like device which appears to be a UV lamp.

The attached pic shows the lamp lights up if start is pressed. Do you think this checks out OK, looking at the attached pic?

The paddle/slotted plate and its mountings have not been disturbed and is tightly clamped to the arm base. However, it is possible that the plate may have been disturbed slighly upwards when I removed the sensor below. I will re-check this now and check its position according to the manual.

The oil there has been cleaned up completely. No longer an issue.

Thankyou once more for your valuable tips and input. I will follow them all until the problem is solved.

Regards

andre/dauphine