Help with Technics SP10 Mk2 speed problem

Johan*

New Member
Hey all

I have a Technics SP10 Mk2 which is giving me some speed problems, it would lock onto 78rpm but not 33 and 45rpm. I have checked voltages on the power supply and they are all correct, I have also swapped all the boards inside the turntable with spare ones I have except for the logic board which I don't have a spare of. I also replaced all the electrolytic capacitors on the logic board but the problem still persists. What else could be causing this?

A little history about this particular SP10: I bought it as "non working", the logic board was damaged. After some months I managed to find replacement boards, I swapped the faulty logic board with the new old one and the table was running fine. 33rpm and 45rpm locked on to speed and ran fine, 78rpm was not getting up to speed but I thought nothing of it as I do not listen to anything at this speed. So I started building a plinth, mounted the table and tonearm and switched it on. Now 33 and 45rpm wouldn't get up to speed but 78rpm was fine..
 
There's a high probability your MN6042 chip could have finally gone (this is a known weakness of the SP10 MK2 and SP15). Fidelis Analog makes a replacement (FC6042) daughterboard that works very well if that is the case.

-D
 
I'm hoping it's not the MN6042 chip, I hate soldering those things. Would a failed MN6042 chip cause it to spin slower than normal? From what I have read a failed MN6042 chip would cause the platter to spin at very high speed which mine does not do, mine spins slower than it should almost like it's not getting enough current to get up to speed. It sort of vibrates while spinning.
 
MK2 doesn't have an MN6042, but thanks for the consideration all the same.

When you measured supply voltages, did you do so with the 'table running? Has the PSU been recapped? Accurate meter? Do you have a scope?
 
Ok ignore what I said above about the platter spinning too slow, I had another look and it is actually spinning way too fast. The PSU has been recapped but not by me and I am also not sure how long ago, the caps all look pretty new. I haven't measured the voltages yet while the table was running, will do so this weekend when I have more time. I don't have a scope but know someone who does, he's away on holiday at the moment though. If I haven't located the problem before he get's back I'm gonna take the PSU to him to have a look at.
 
Yes, measure under load. It doesn't change a lot, but does change a little. It's very sensitive to the logic supply (5V). You want to be as close to 5V as you can get - 4.9 to 5.1 typically. It's also sensitive to ripple especially on that supply.

If the motor runs away - well over 100RPM - it's typically a sign of the FG signal not getting through. If it won't lock at speed but isn't running away and surges it's probably something with the PLL. There are two VR on the control board - one for 33/45, and one for 78. If these are way out the PLL won't lock. You do need a scope to set these correctly. Assuming supply voltages are correct and there's no excess ripple.
 
The motor is definitely running away, I can't say at what rpm but much faster than it should. By FG signal do you mean the quartz signal? What could be preventing this signal from getting through? Dry solder joints perhaps? Haven't really looked for any of those.
 
The SP 10 Mk II is Quartz locked. It does not use the occasionally trouble prone IC that the SP-15 and SP 10 MK III use.
 
Last edited:
The SP 10 Mk II is NOT Quartz locked. FG= Frequency Generator, servo locked DD.

Are you sure about this? According to the specifications on vinylengine the SP10 Mk2 is quartz-controlled phase-locked servo circuit, or is this different to quartz locked?
 
It is quartz locked. I think Kent is thinking of the original SP-10.
 
MK2 doesn't have an MN6042, but thanks for the consideration all the same.

When you measured supply voltages, did you do so with the 'table running? Has the PSU been recapped? Accurate meter? Do you have a scope?

Is that only the SP10 Mk3 then?

Whoops.

-D
 
Been there, done that. Your voltages are NOT correct, no matter what your unloaded test results may be.

1) Completely recap the power supply. (As KentT can attest, this was just a standard thing to do on a regular basis, even on fully working tables, when they were still in radio station use.)
2) Adjust the voltages while the table is running so the power supply is under load.
3) Make sure your multimeter is a good one, you need to get it as close to perfectly set on the nominal voltages as possible to get it to behave.
 
Yes, that power supply must be recapped if not done within the last 2-5 years, and those voltages outputted must be right on specification called for in the service manual. And they must be adjusted with the turntable on, under load, and yes, you need a good accurate multimeter for this. Those voltages need to be very close to if not perfectly set, and that power supply output must be clean and ripple free. As those voltages are critical for the feedback loop to work correctly. When these machines were on air, and I maintained them, this was an every 3-5 year maintenance item to keep the turntable reliable every day.
 
I got the power supply back yesterday from a friend who checked it out on his oscilloscope, he couldn't find any ripples and says the psu is 100%. Got home and decided to plug the turntable in and now 33 and 45rpm runs fine again, 78rpm not. This is exactly what it was doing before so I don't expect it to stay like this for too long. Weird thing is when I press stop all the speed led's come on, the one which speed is selected being bright and the other two very faint.
 
Kent used to service these things in radio stations all the time. Listen to him. Unloaded test results on these power supplies don't mean jack.
 
The power supply has been completely recapped, I did this myself before taking it to the friend. I did ask him to also test it under load so I assume that is what he did. I'll hook my dmm up to the table while it's on and and take some measurements just to be sure.
 
Good to know - your symptoms tend to be a classic example of PS issues. Do you have the service manual? If so, you're probably going to have to start working through the process flowcharts with a multimeter to find out what's going on.
 
Back
Top Bottom