Realistic Lab 400 Speed Problem

[jamesc760]

It changes from day to day. I mean, I set the speed today and it's rock steady; tomorrow, it's slow. Time for a re-cap?

Any other Lab 400 owners having this problem?

 

[pworm14]

You most likely just need to clean/deoxit the doors control pots. My lab 420 would wander a bit and a good cleaning of the pots cured that issue.

It's easy and definitely worth a shot.

 

[jamesc760]

Ok, thanks for the suggestion, @pworm14 !

Another strange thing happened after my original post above; I was playing a record and on the last track, the platter started to slow down a lot, I was surprised and when I looked at my Lab 400, I could see it was turning really slow, so I started to turn the pitch control but I ran out of the pot limit. So, something's really wrong with my tt. Do you still think deoxit will fix it? I'm going to try it anyway.

 

[pworm14]

It might. Start with the deoxit on the pots and see what happens. Clean them throughly, a couple of times. You may be surprised.

 

[jamesc760]

It's a pain to open the bottom panels; there are two dozen screws that you have to unscrew. Applied a first coat of CRC Electronics cleaner on the speed control pots, both 33 and 45, and then the 2 switches. There's a set of leaf/reed switches, check them to see if any were corroded, didn't see any, so left those alone for now. I'm just gonna let it dry overnight; then I will apply DeOxit D5, hopefully it will solve the problem.

 

[jamesc760]

Applied DeOxit D5 on both 33 and 45 pots, also on pots on the board as well. It's still not stable on speed. If rest it, the next time it plays, the speed is sometimes faster or slower than before, each and every time. It doesn't stick.

 

[tnsilver]

Time for a re-cap?

Now is. Do the entire servo control, and PS PCB's. Swap out all the old Rubycon EC's.

 

[jamesc760]

I was hoping the deoxit would fix the problem...

Does anyone have a list of all the capacitors in the lab 400?

 

[jamesc760]

Found and downloaded a service manual. There are 2 electrolytic capacitors:

C103 - 470 uF 50V
C104 - 100 uF 25V

These electrolytic capacitors are connected directly to TR101, the lone transistor in the table. Sometimes when an e-cap goes bad, it takes the transistors/ic's along with it. Hopefully, that's not the case here.

I am going to rummage through my parts bins to find these 2 e-caps, should be easy fix.

 

[tnsilver]

There are 2 electrolytic capacitors... ...should be easy fix

Yes, but not that easy. That's just the power supply EC caps. The rest of them are in the servo control PCB, in the grayed out part of the SM, where it oddly says 'not serviceable'. You're gonna have to pry that motor open and do some de-soldering to access those parts that really need swapping out.

 

[jamesc760]

Doh, I spoke too soon! Of course, it can't be that easy!! What was I thinking???

Thank you to @tnsilver for pointing out the other hidden e-caps in the servo control PCB. I only saw there are 3 PCB's in Lab 400: Phono, Auto and Supply PCB. I had no idea there was a servo control PCB in the motor. This is going to be fun, tearing open the motor chassis.

 

[pworm14]

Did you just spray the pots? You have to spray out in there and swipe the pots back and forth about 30 times, really fast, for it to clean the contacts.

 

[jamesc760]

I DID spray the pots with CRC Electronics Cleaner and with DeOxit D5 the next day. I DID swipe the pots back and forth for about 50 times, pretty fast. My fingers hurt afterwards. About a month ago, I did spray the pots with CRC Electronics Cleaner also. That seemed to help, for a while until the other day when it started acting up.