Realistic LAB-400 Speed (Motor?) Problems

[spence0nasty]

I picked up a Realistic LAB-400 the other day and when I got it home and started to clean it I noticed that the platter was spinning a little inconsistently. I took the platter off to get a better look and the motor isn't spinning consistenly, instead it turns in short bursts. Here's a video of the motor in action:

http://youtu.be/pjetREylSuU

At the 11 second mark I switch from 33 to 45 to show that the speed problem exists on both settings. I pulled the service manual off of VinylEngine and measured the voltages on my PCB to check if everything was up to snuff. The full schematic is attached to this post but the PCB of interest is embedded below:

Here are my measurements:

Emitter of TR101: 15.6VDC
Collector TR101: 20VDC
Base of TR101: 16.3VDC
O/P of T101 (transformer): 20VRMS

These all look fine to me, they're a little lower than the schematic but not so low as to cause this kind of intermittency. Has anyone had similar problems? Any idea what to troubleshoot next?

 

[Balifly]

It is not a good idea to run the direct drive motor without the platter for long period.

You may incur damage to the motor. :scratch2:

 

[spence0nasty]

Thanks for the tip, I won't run it any longer except when I need to test any fixes I end up doing to it. I only ran it without the platter for about 5 minutes total today so hopefully I didn't do it any harm.

 

[Metalownz]

Its supposed to run like that. My suggestion is clean the 33-45 pots and your speed will return to normal.

 

[number13]

The platter acts a flywheel, helping to smooth out the speed. Do not run the table without it. As suggested, clean out the 33 & 4 5 pots and replace the power switch.

 

[spence0nasty]

The platter acts a flywheel, helping to smooth out the speed. Do not run the table without it. As suggested, clean out the 33 & 4 5 pots and replace the power switch.

Now that I've learned this is how the motor works I'm kind of embarassed I even asked this question. Oh well, you gotta learn somehow and what better way than asking stupid questions?

Why is it necessary to replace the power switch? I'm asking because this TT doesn't quite work like my other two TTs and I'm wondering if the power switch is the cause. On my other tables (Dual 1246 and Sony PS-LX2) I can use the cueing lever to raise the needle over the record and the platter automatically starts to spin. Likewise, I can use the cueing lever to raise the needle off of the record and manually return the arm to the rest and the table will automatically shut off. With this table I have to use the automatic start/stop functions to start/stop the platter which basically renders the cueing lever obsolete. Is this normal for a LAB-400 or are there some electronics that aren't working correctly?

 

[Balifly]

On my other tables (Dual 1246 and Sony PS-LX2) I can use the cueing lever to raise the needle over the record and the platter automatically starts to spin. Likewise, I can use the cueing lever to raise the needle off of the record and manually return the arm to the rest and the table will automatically shut off. With this table I have to use the automatic start/stop functions to start/stop the platter which basically renders the cueing lever obsolete. Is this normal for a LAB-400 or are there some electronics that aren't working correctly?

Have a look through the owner's manual.

It has instructions on how to use the various buttons and the curing mechanism (page 6).
http://www.vinylengine.com/library/realistic/lab-400.shtml

 

[Montycat]

Now that I've learned this is how the motor works I'm kind of embarassed I even asked this question. Oh well, you gotta learn somehow and what better way than asking stupid questions?

I thought it odd when I first saw that effect on DD tables. But I am aware of it now...

Why is it necessary to replace the power switch?

I'm curious about that one myself. :scratch2:

I'm asking because this TT doesn't quite work like my other two TTs and I'm wondering if the power switch is the cause. On my other tables (Dual 1246 and Sony PS-LX2) I can use the cueing lever to raise the needle over the record and the platter automatically starts to spin. Likewise, I can use the cueing lever to raise the needle off of the record and manually return the arm to the rest and the table will automatically shut off. With this table I have to use the automatic start/stop functions to start/stop the platter which basically renders the cueing lever obsolete. Is this normal for a LAB-400 or are there some electronics that aren't working correctly?

It is normal and not just for the LAB-400. The cue lever can still be used if for example you want to skip tracks or clean the record while it's turning. It still has a purpose.

 

[spence0nasty]

I've been reading the service manual and I'm still not sure what the benefit of replacing the power switch is. However, there is one switch listed in the manual that might need replaced on my TT and it's the muting switch. When I hit the STOP/REJECT button the left channel mutes but the right channel sort of just lowers in volume. I haven't cleaned any of the contacts yet as I'm still waiting on a new can of Deoxit in the mail so maybe that's all it needs.