Technics Sp10 Woes
#1 Technics Sp10 Woes
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?
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?
#2
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.
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.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#4
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.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#6
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.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#9
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
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
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#10 Re: Technics Sp10 Woes
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
Regards
Wolfgang
#11 Re: Technics Sp10 Woes
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.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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#12 Re: Technics Sp10 Woes
Will try that tonight, thank you.
Wolfgang
Wolfgang
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#13 Re: Technics Sp10 Woes
Hi Nick, can you please point me in the right direction, possibly a Transistor number and a resistor number.
#14 Re: Technics Sp10 Woes
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.
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.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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#15 Re: Technics Sp10 Woes
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?