technics sl-dl1 linear turntable repair questions

[stanwebber]

i got a hold of a non-working technics sl-dl1 that i'm working on to restore to operation. it was missing the repeat and cuing buttons and there was a loud clanking sound coming from the upper cabinet when raised. i removed the tonearm dustcover to investigate and found the tonearm belt off and the clanking sound resulting from the larger brass belt pulley loose off the shaft. a small washer was still stuck to the pulley on one side while the other side had a hardened translucent substance covering the shaft hole. i cleaned up the worm drive shaft with alcohol, applied a little locktite to the end then reassembled the washer and pulley and let it set. i reapplied some super lube grease between the washer and pulley and also hit the plastic worm gear and large gear wheel. while i was at it i used some super lube ptfe oil on the drive rails.

i put on a new drive belt and powered everything on, but the tonearm would only return to the rest position and nothing else. after a few moments i realized the reset switch on the lower cabinet wouldn't be depressed unless i reattached the tonearm dustcover at which point i discovered the manual record size selector was hanging with a broken tab. i poked thru the selector openings with a toothpick and got everything aligned and screwed back on. this time everything started working, but i still have some concerns and questions for someone else who has had this turntable.

1. my primary concern is an audible clicking sound when the tonearm is manually cued forward. the belt/drive rope is not slipping as the speed is dead constant at both slow & fast cue speeds. the clicking sound is at regular half second (or faster) intervals completely synced to the cue speed. the sound is totally absent when cuing backwards. this can't be normal can it? what could be causing the noise?

2. while lubricating the tonearm mechanism i noticed 4 or 5 stiff points (near the middle of travel) when moving the drive pulley by hand. i added additional grease and ran the worm gear back & forth over them, but the stiff points stubbornly remain. the drive rails were completely free of debris...only dry lubricant had ever been used on them before i added ptfe impregnated oil. could the large plastic gear wheel be damaged--visually the gears look unblemished? where else to look as this has to impact the smooth operation of the tonearm?

3. do the front panel buttons just pop out? despite the button being missing i can still operate the repeat and cuing functions with a stick.

4. what's the deal with no 45rpm adapter?

 

[stanwebber]

i taped over the reset switch and record size sensors and was able to observe the tonearm cuing in action close up. the clicking sound is actually the tonearm being jerked forward. i can visually see the tonearm carriage rhythmically bouncing up & down as it is being pulled along. i don't understand what could be causing this as the carriage action is butter smooth going the other way so the guide rails aren't out of alignment.

the drive rope is uniformly covered in a thick black substance, but i've seen mention of this in several other forums so i'm thinking whatever it is is factory. in any case it absolutely causes no problems when the tonearm cues backwards.

also, is there something weird about the t4p cartridge screw? mine sort of looks like part of the threads closer to the tip are stripped, but it looks so uniform i'm not sure. i also notice there are threads on both sides of the cartridge socket which i've never seen before.

 

[gadget73]

Its a shoulder screw if I remember right. Should be about 1/4" of threads and the shoulder is about 3/8". I do not recall a pilot or anything on the end where it would look like missing threads.

Are the position sensors on the arm working properly? If they are sticky or if the arm doesn't swing back and forth smoothly to trigger them the servo action will be jerky. There is also an adjustment for the gain on that, but you need some specific pitch record in order to set it correctly or it doesn't work right. I screwed up the one I used to have.

 

[stanwebber]

my screw has threads all along the length--a screw with a raised shoulder wouldn't work as i mentioned there are threads on both sides of the cartridge socket which i've never seen before. basically, it looks like about 1/8in of the threads are stripped approx 1/8in down from the tip. i don't have any problems securing the cartridge with the screw...it's just an oddity. i own 8 (not including this one) other t4p turntables and having threads on both sides is a first for me so i thought the screw might be a special deal

the position sensors on the tonearm seem to operate fine, although i haven't done any critical listening yet. it certainly hasn't skipped at all on the few records i've sampled.

 

[stanwebber]

at this point all old lubrication has been cleaned off/replaced and the forward cuing jerking/vibration still remains. the only possible culprit i can point to now is the stiffness of the tonearm cables causing an imbalance with the forward motion of the tonearm sled--flexing on forward cuing and unwinding when reversed. the cables don't contact any surface until near the end of the tonearm movement where the contact point is freshly lubricated with grease.

if this is indeed the case then everyone who owns these turntables (sl-7/dl1/ql1) must experience this behavior to some lesser or greater degree and not notice or realize it or just not care.

 

[stanwebber]

i want to focus in on the worm drive gear. i wish i had another unit for comparison, but maybe someone else out there has their sl-7/ql1/dl1 apart right now for maintenance and can answer these questions.
1. is there anything else besides a single washer between the brass belt pulley and the stanchion upright?
2. how much side-to-side play is there in the worm drive shaft? is there more than 1 or 2mm of movement side-to-side? barely any?
2. approximately where does the pinwheel (black slotted disc opposite end from pulley) sit in the gap between the optical sensors. is it exactly in the center of the circuit board slot? towards one side or the other? if there is side-to-side play in the shaft where does the pinwheel movement fall in the gap?