Technics SP10 mk2 - no electronic brake...

Love it or hate it, it just won't stop
Shovel_Knight
User
Posts: 7
Joined: Tue Jul 16, 2019 8:34 am

#1 Technics SP10 mk2 - no electronic brake...

Post by Shovel_Knight »

Hi,

Long time lurker - first time poster here.

I have a Technics SP10 mk2P/L (an ex-BBC unit) which is a bit unwell.

It mostly works apart from the electronic brake. The symptoms are as following: the turntable spins up and locks speed, but if I switch from 45 to 33 or from 78 to 45 or 33 it slowly spins down instead of adjusting the speed immediately.

When I first got it, it had trouble locking, but it now locks OK after I adjusted the PLL timings with the help of my USB oscilloscope (Bitscope Micro).

I checked TR210 on the logic board (which apparently controls the electronic brake) and the voltage at the collector matches the service manual. There is good connection between B1 on the logic board and b1 on the drive board.

I checked the voltages at TR15, TR36, TR37, TR17, TR18, TR21, TR22, TR25 and TR26, as mentioned in the service manual, and I got the following results:

TR15
E: 15.8V (should be 16V)
C: 20.7V (should be 21V)
B: floating between 14.3~14.7V (should be 15V)

TR36 start
C: 16.18V (should be 15V)
B: –0.02V (should be 0V)

TR36 stop
C: 0.006V (should be 0.01V)
B: 0.67V (should be 0.68V)

TR37 start
E: 17.81V (should be 18V)
C: 0V (Should be 8V)
B: 20.74V (should be 20V)

TR37 stop
E: 15.18V (should be 15V)
C: 15.17V (Should be 15V)
B: 14.49V (Should be 14V)

TR17
E: 21V (21V)
C: 30.9V (31V)
B: 21.05V (21V)

TR18 start
E: 15.13V (should be 17V)
C: floating between 0.2~0.7V (should be –1V)
B: 21.05V (21V)

TR18 stop
E: 14.3V (14V)
C: 0V (Should be –1.5V)
B: 21.05V (n/a)

TR21
E: floating between 20.1~20.7V (21V)
C: 30.9V (31V)
B: 21.05V (21V)

TR22 start
E: 15.14V (17V)
C: floating between 0.2~0.7V (–1V)
B: floating between 20.1~20.9V (21V)

TR22 stop
E: 14.35V (14V)
C: 0V (Should be –1.5V)
B: 21.05V (n/a)

TR25
E: 20.75V (21V)
C: 31.25V (31V)
B: n/a (n/a)

TR26 start
E: 15.15V (should be 17V)
C: floating between 0.2~0.7V (Should be –1V)
B: n/a (n/a)

TR26 stop
E: 14.5V (14V)
C: 0V (–1.5V)
B: n/a (n/a)

So the voltages are off. Some of them are somewhat off, and some are completely off (TR37, TR18, TR22, TR26).

I also tested all the transistors on the drive PCB using my Chinese component tester. They all tested OK except two:

TR15 is correctly detected but the tester shows hFE = 0 and forward voltage of just 112 mV instead of ~600mV
TR37 is detected as a diode.

Of course, those anomalies could be caused by testing the components in situ.

I'm a bit unsure as to what should be my next step, because I'm not a huge expert in electronic circuits.

If somebody could help me, I would be very grateful, because I really want to get this magnificent drive unit to work perfectly again...
User avatar
Nick
Site Admin
Posts: 15711
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#2 Re: Technics SP10 mk2 - no electronic brake...

Post by Nick »

Does the break actually engage?
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
Nick
Site Admin
Posts: 15711
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#3 Re: Technics SP10 mk2 - no electronic brake...

Post by Nick »

Reading what you are saying, I don't think the break is meant to engage just changing down speed, only when its actually stopping.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Shovel_Knight
User
Posts: 7
Joined: Tue Jul 16, 2019 8:34 am

#4 Re: Technics SP10 mk2 - no electronic brake...

Post by Shovel_Knight »

How do I check it? :)

I know that the mechanical brake engages perfectly (I can hear the solenoid clicking and the platter stops immediately), but how can I check if the electronic brake engages? The service manuals advises to simply check the voltages on the drive PCB.

The electronic brake circuit should be controlled by TR210 on the logic board and the voltage there drops as expected when the turntable is stopped.
Shovel_Knight
User
Posts: 7
Joined: Tue Jul 16, 2019 8:34 am

#5 Re: Technics SP10 mk2 - no electronic brake...

Post by Shovel_Knight »

This is what the service manual says about the electronic brake.
Screenshot 2019-10-28 at 11.03.43.png
User avatar
Nick
Site Admin
Posts: 15711
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#6 Re: Technics SP10 mk2 - no electronic brake...

Post by Nick »

Ok, so we are talking about slowwing down, not a break other than a signal to the electronics. Did you see how the phase lock operated when slowing?

How long does it take to go from 45 to 33?
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Shovel_Knight
User
Posts: 7
Joined: Tue Jul 16, 2019 8:34 am

#7 Re: Technics SP10 mk2 - no electronic brake...

Post by Shovel_Knight »

Nick wrote: Mon Oct 28, 2019 11:33 am Ok, so we are talking about slowwing down, not a break other than a signal to the electronics. Did you see how the phase lock operated when slowing?

How long does it take to go from 45 to 33?
Yes, slowing down - Matsushita themselves call it "electronic brake". I believe it uses the reverse drive circuit.

When I go from 45 to 33, the speed unlocks and it may or may not eventually lock again when the platter slows down to 33 RPM on its own. It usually takes upward of 30 seconds.

If I try to slow the platter down with my finger, it locks the speed immediately.
User avatar
Nick
Site Admin
Posts: 15711
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#8 Re: Technics SP10 mk2 - no electronic brake...

Post by Nick »

Ok, its not a problem I have seen before, so I think you are doing what I would do. Possibly check the transistors after removing them component checkers normally can't be used in circuit.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
Nick
Site Admin
Posts: 15711
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#9 Re: Technics SP10 mk2 - no electronic brake...

Post by Nick »

T37 seems the odd one, I would check that out of circuit. The collector voltage seems odd, and may be the cause of the following voltages veing slightly higher than expected. Bit confused how 36b and 37c can be that different, maybe check the 47k resistor between them.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Shovel_Knight
User
Posts: 7
Joined: Tue Jul 16, 2019 8:34 am

#10 Re: Technics SP10 mk2 - no electronic brake...

Post by Shovel_Knight »

Thanks!
Wolfgang Felber
User
Posts: 75
Joined: Wed Nov 08, 2017 10:18 pm

#11 Re: Technics SP10 mk2 - no electronic brake...

Post by Wolfgang Felber »

Hi Nick, interesting, reading the last post, I have set up the non working, now working SP10 with an arm and cartridge. I have been listening and enjoying but every so often, the platter slows down, not slowly but quickly and then returns to normal speed. It is as if there was a brake put on it. I can not hear the brake solenoid click, so I am wondering if the internal motor brake is activating. I know that should not happen but it seems odd because as soon as it slows it returns to normal speed. From my understanding the motor goes into reverse to brake as well as using the solenoid. Is there any possibility that a reversing current could be going through the system? Possibly caused by bad logic voltage?
Regards
Wolfgang
User avatar
Nick
Site Admin
Posts: 15711
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#12 Re: Technics SP10 mk2 - no electronic brake...

Post by Nick »

Its possible, how often does it do it?
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Wolfgang Felber
User
Posts: 75
Joined: Wed Nov 08, 2017 10:18 pm

#13 Re: Technics SP10 mk2 - no electronic brake...

Post by Wolfgang Felber »

Hi Nick, once possibly twice per side.
User avatar
Nick
Site Admin
Posts: 15711
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#14 Re: Technics SP10 mk2 - no electronic brake...

Post by Nick »

Ok, maybe worth watching the break signal while its playing and see if it goes high.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Shovel_Knight
User
Posts: 7
Joined: Tue Jul 16, 2019 8:34 am

#15 Re: Technics SP10 mk2 - no electronic brake...

Post by Shovel_Knight »

Long story short - the issue was with TR210 on the logic board. I replaced it and now the turntable runs perfectly.
Post Reply