#76
Posted: Tue Oct 30, 2012 10:50 am
Me back again...
Some more experience with the SP10s. I was given two, one in sad condition and the other in fair condition, both without power supplies (no SH10s). I intended to make one good one out of the pair.
I built a power supply using a scrap-box transformer (15-0-15v 2a and 6v 3a) with voltage regulator chips: 5v 1a for the 5v rail and scrap box 20v 1a plus a zener or two and a high power NPN transistor to get voltage up to 32.5v and current up to 3a). A couple of suitable electrolytics on each rail and I was in business. In fact, all scrap-box except the 5v regulator and the 4pin connector. NB. No 140v rail because I was going to replace the failing or dud neon strobe tubes with LEDs.
The first table to go on the bench was the suspected dud.
In my earlier posts I have outlined my accidental shorting of the 5v rail to the 32v rail. 20 hours, 16 sockets and a few TTL chips later...
It responded to additional care but I couldn't get the signals on my scope to line up like the manual when adjusting VR101 and VR102. In fact, I discovered that, when I connected the scope probes (an old Philips dual beam scope) it actually influenced the signal shapes and timings, there must be some probe capacitance/resistance issues. I eventually found that adjusting VR101 while watching the strobe LEDs seemed just as effective (at 33.3 turn VR101 until table increases speed, then turn pot back until table decreases speed and then turn pot to central point of stable speed. Repeat on 78 with VR102. Please advise if you think this is shaky advice...
WATCH OUT for shorted probes. Probe points 0v, S and T are direct connections to the circuitry and are not isolated by resistors or whatever. I had to replace one transistor due to probe shorting (scrap-box again, thank goodness).
Apart from that, and a moment when a badly soldered +5v wire broke off and shorted on the plate, all went well. I went from happiness to despair about 4 times that afternoon.
I carefully oiled and cleaned up the bearings and it works 100%. The Technics label is gone long in the past (anyone know where I can get one?) but the table itself is essentially good.
The second SP10 responded well to a wiser and poorer man and I managed to get it humming, also with new LED strobe, without much difficulty.
So now I have one I use and a spare. Looks like my old Garrard 301 will not be missed so much any more...
Thanks for listening, I appreciate any comments if you think I have missed something.
Some more experience with the SP10s. I was given two, one in sad condition and the other in fair condition, both without power supplies (no SH10s). I intended to make one good one out of the pair.
I built a power supply using a scrap-box transformer (15-0-15v 2a and 6v 3a) with voltage regulator chips: 5v 1a for the 5v rail and scrap box 20v 1a plus a zener or two and a high power NPN transistor to get voltage up to 32.5v and current up to 3a). A couple of suitable electrolytics on each rail and I was in business. In fact, all scrap-box except the 5v regulator and the 4pin connector. NB. No 140v rail because I was going to replace the failing or dud neon strobe tubes with LEDs.
The first table to go on the bench was the suspected dud.
In my earlier posts I have outlined my accidental shorting of the 5v rail to the 32v rail. 20 hours, 16 sockets and a few TTL chips later...
It responded to additional care but I couldn't get the signals on my scope to line up like the manual when adjusting VR101 and VR102. In fact, I discovered that, when I connected the scope probes (an old Philips dual beam scope) it actually influenced the signal shapes and timings, there must be some probe capacitance/resistance issues. I eventually found that adjusting VR101 while watching the strobe LEDs seemed just as effective (at 33.3 turn VR101 until table increases speed, then turn pot back until table decreases speed and then turn pot to central point of stable speed. Repeat on 78 with VR102. Please advise if you think this is shaky advice...
WATCH OUT for shorted probes. Probe points 0v, S and T are direct connections to the circuitry and are not isolated by resistors or whatever. I had to replace one transistor due to probe shorting (scrap-box again, thank goodness).
Apart from that, and a moment when a badly soldered +5v wire broke off and shorted on the plate, all went well. I went from happiness to despair about 4 times that afternoon.
I carefully oiled and cleaned up the bearings and it works 100%. The Technics label is gone long in the past (anyone know where I can get one?) but the table itself is essentially good.
The second SP10 responded well to a wiser and poorer man and I managed to get it humming, also with new LED strobe, without much difficulty.
So now I have one I use and a spare. Looks like my old Garrard 301 will not be missed so much any more...
Thanks for listening, I appreciate any comments if you think I have missed something.