Technics Sp10 Woes

Love it or hate it, it just won't stop
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chris78
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#1 Technics Sp10 Woes

Post by chris78 »

Ok here goes,

I acquired an sp10 p/l and psu a while back and have recently been trying to get it going.

The Psu which I should point out is an 'A' version was the first to sort which was easy enough, a refresh of the capacitors and zeners was enough to get this going, voltages correct and nice and stable.

So on to the table itself, its been completely recapped and TR5 was found to be faulty on the drive pcb, I wanted the start stop to work as intended on a domestic sp10 and after a long search I found someone with a spare logic board from a regular sp10, anyway long story short the board was confirmed working, but has had IC8 replaced with a 74hct73 to my annoyance the start/stop button needs to be held in to make the motor spin, thinking that this IC maybe faulty I replaced it with a 74LS73 now the start/stop still needs to be held in but this time to stop the platter, everything else voltage wise seems to check out so I'm at a loss, does anyone have any ideas?
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Nick
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#2

Post by Nick »

Yes, I had to fix the same problems when replacing all the logic. I don;t have time now but I will check the schematic and see if I can remember what the problem was and the fix.

I think the problem was the input conditions were different so the older slower logic saw one pulse, now it sees two so end up where it started.
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chris78
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#3

Post by chris78 »

Nic you are a gent.

I have seen a few posts of yours and others on the forum about replacing the logic chips, great work!
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Nick
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#4

Post by Nick »

If its the same as my MkII circuit, the problem is the 43k load resistor of the transistor that drives the flip flop. In input to the flip flow and the high load causes a double trigger. Change the 43k to a 4k7 or something of that order (or just add it in parallel) and see if that helps.
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chris78
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#5

Post by chris78 »

Hi Nick, thanks for the reply,

With the load resistor on TR207, its R221 which is 4k7 already, value wise lower this to less to 1K?

Thanks
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Nick
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#6

Post by Nick »

Yes, try it, I can't remember off hand what values I used. I will check on the other (also modified) logic board I have somewhere.
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chris78
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#7

Post by chris78 »

Ok, thanks
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Nick
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#8

Post by Nick »

Yep, 1k in parallel with the original 4k7
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chris78
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#9

Post by chris78 »

Thanks for the reply,

tried the 1K in parallel, no change, should I go lower?

Just to check we are increasing the current to the drive transistor?

Also do you know why the LS and the HCT chips are behaving in reverse with the fault, i.e. the LS applies the break whilst the button is held, and the HCT spins whilst the button is held
Wolfgang Felber
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#10 Re: Technics Sp10 Woes

Post by Wolfgang Felber »

Hi all, tried the 1.5K resistor in parallel with 4.7k resistor no 221, success, got it to stop and start when required. Will try a few other values around that mark to see if I get a better response. My next problem is it still runs at hyperspeed, no control over speed. the speed switches are working correctly as I checked the voltages as per manual. Any help will be greatly appreciated. I am so close to fixing this thing, just one more step.

Regards

Wolfgang
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Nick
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#11 Re: Technics Sp10 Woes

Post by Nick »

I don;t have the schematic in front of me, but the logic circuit has a similar NPN driving a flip flop at he bottom of the diag, the bit on the right at the bottom that drives the phase comparator. Try doing the same 1k resistor across the 4k7 in that as well, that may help.
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#12 Re: Technics Sp10 Woes

Post by Wolfgang Felber »

Will try that tonight, thank you.

Wolfgang
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#13 Re: Technics Sp10 Woes

Post by Wolfgang Felber »

Hi Nick, can you please point me in the right direction, possibly a Transistor number and a resistor number.
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Nick
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#14 Re: Technics Sp10 Woes

Post by Nick »

R264 on TR221

Beyond that, I would use a scope to check the waveforms are as shown on the diag. You will need a scope to setup the phase lock anyway.
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Wolfgang Felber
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#15 Re: Technics Sp10 Woes

Post by Wolfgang Felber »

Hi Nick, I tried what you suggested last night, unfortunately it did not make a difference, I looked at the circuit diagram again and noticed there are two transistors that feed IC 9 and 10. do you think it would be a good idea to do the same to the resistor that feeds tr 220 as well?
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