Sounds like the TT is drawing too much current from the 5V supply, hence the drop across the cable; or the cable/connector has too high a resistance.
When I have come across this sort of thing before I use an infra-red thermometer to quickly check for any overheating chips. They're very cheap these days, and very useful.
Handheld LCD Digital Laser Thermometer Temperature Infrared Non-Contact IR Gun | eBay
One advantage is that the 5V supply is used to power all the logic, even when the platter is not rotating, so these checks can be done with the deck on its side and the under cover removed.
When I have come across this sort of thing before I use an infra-red thermometer to quickly check for any overheating chips. They're very cheap these days, and very useful.
Handheld LCD Digital Laser Thermometer Temperature Infrared Non-Contact IR Gun | eBay
One advantage is that the 5V supply is used to power all the logic, even when the platter is not rotating, so these checks can be done with the deck on its side and the under cover removed.
Dave, yes, the service manual suggests 5v at both ends. What next?
Ralph, I'm not sure if you followed the history of my problems. Basically, it was rotating backwards but locked in speed. I then shorted across C2 and C4 on the connecting board accidentally, and since then it has stopped spinning (backwards).
I think I have one of those infrared temp guns somewhere. Let me check.
Ralph, I'm not sure if you followed the history of my problems. Basically, it was rotating backwards but locked in speed. I then shorted across C2 and C4 on the connecting board accidentally, and since then it has stopped spinning (backwards).
I think I have one of those infrared temp guns somewhere. Let me check.
C2 and C4 on the connecting board. It stopped the turntable from spinning backwards.
Sucks that you won't be able to help. I have appreciated the support so far. I'm going to keep trying starting with the PS and getting the 5V line back up to 5V. I measured the current draw yesterday and it was 0.96 A on the 5V line (voltage measures 4.86V on the connecting board). Is 0.96A in the ballpark for the 5V line? The fuse is 1A.
Sucks that you won't be able to help. I have appreciated the support so far. I'm going to keep trying starting with the PS and getting the 5V line back up to 5V. I measured the current draw yesterday and it was 0.96 A on the 5V line (voltage measures 4.86V on the connecting board). Is 0.96A in the ballpark for the 5V line? The fuse is 1A.
C2 is the 5V feed, and C4 the 32.5V supply. Sadly, connecting them together is not a good idea, even for a split second.
Most likely you will have damaged/destroyed all the logic chips
With luck and skill it is possible to recover from this situation, but unless you are very adept at soldering, and have access to a professional vacuum desoldering station, you are most likely on a hiding to nothing
Have a look here for more info :-
SP10 fun - audio-talk
This is the page with the list of parts you're most likely to need to replace
SP10 Troubles - Page 5 - audio-talk
Most likely you will have damaged/destroyed all the logic chips
With luck and skill it is possible to recover from this situation, but unless you are very adept at soldering, and have access to a professional vacuum desoldering station, you are most likely on a hiding to nothing
Have a look here for more info :-
SP10 fun - audio-talk
This is the page with the list of parts you're most likely to need to replace
SP10 Troubles - Page 5 - audio-talk
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As Ralph said, C2 and C4 are the points on the connecting board where the 5V and 32.5V lines come into the table.
If there are a bunch of chips that are dead, I don't want to get into desoldering and soldering them (I do not have a desoldering iron). How do I test whether the chips are dead?
Are there donor boards from other non-working table available? Several folks here had bought two tables... maybe one was never restored. Could I borrow entire boards from them? What are my options?
Ralph, that first link is excellent. So, it can be done with some patience. Good to know! I have since bought hook clips and also separated the motor from the table, so that I don't have to work on it upside down.
If there are a bunch of chips that are dead, I don't want to get into desoldering and soldering them (I do not have a desoldering iron). How do I test whether the chips are dead?
Are there donor boards from other non-working table available? Several folks here had bought two tables... maybe one was never restored. Could I borrow entire boards from them? What are my options?
Ralph, that first link is excellent. So, it can be done with some patience. Good to know! I have since bought hook clips and also separated the motor from the table, so that I don't have to work on it upside down.
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Yeap, 1A is way too high. I had the same problem on my dead SP10-MK2. But lucky for me I have a good, working one. To fix this board you need at a minimum, scope, good desoldering hand pump, good desoldering station, and for this particular problem a lab power supply, preferably with adjustable current limiter.
If your 32V went on the 5V line, probably all the digital IC's are dead, like my own board! There is no simple way to fix this, you can isolate section of the 5V line, and sections of the digital chain, and using the lab power supply, test the board just by itself outside the table. Then measure the 5V power supply current, and touch the supplied IC. On my board, most of the Ic were too hot to touch... Normal board has low current draw, even lower with separate supplied 5V section. If you have more than let's say 100ma current draw for 1/3 of the IC, they are fried...
Now the bad news. These chips are not the usual TTL chips, but the very old, and obsolete DTL type. you neeed DTL, TTL won't work... You can probably find all the chips, as I did on ebay, but they are expensive. Second bad news, the PCB traces are VERY FRAGILE! No way to safely unsolder most of the digital IC without pcb damage. The only safe solution, using a very sharp tip cutter, cut the ic legs from the top, then gently, pull out each pin, one by one. Then using the desoldering pump, clean all the holes, install an IC socket and resolder at low temperature. Then insert the good IC.
As I said, no real point in testing at the start, you need to remove all the IC's... In my case I started from the left, clock oscillator, and move to the right of the schematic. So far i did about 4/5 of the board, testing it all the way according to the schematic voltages and waveforms, that are by the way quite accurate. Now my board is no longer toasting hot, and 5V supply current is almost back to normal.
I'm almost there and then I'll have a very nice, also recap digital board. But it is a long, delicate and somehow expensive job. AND you need to be able to work and test electronics, it is not an amateur job I'm afraid...
I'm away from home but I can post some reference readings once I'm back in October.
Once I'll be done with this repair, I think I'll install an overvoltage protection circuit into my turntable, on the 5V line (resetable fuse and transorb diode). I think that the original problem with this disaster is a defective power supply. If the 5v regulator is failed, it will passthrough the raw dc voltage before the regulator, that is sadly way over 5V, that in turn destroy the Digital board... Pitty there was no protection into the table itself, usually a good thing when you have a detachable external supply.
SB
If your 32V went on the 5V line, probably all the digital IC's are dead, like my own board! There is no simple way to fix this, you can isolate section of the 5V line, and sections of the digital chain, and using the lab power supply, test the board just by itself outside the table. Then measure the 5V power supply current, and touch the supplied IC. On my board, most of the Ic were too hot to touch... Normal board has low current draw, even lower with separate supplied 5V section. If you have more than let's say 100ma current draw for 1/3 of the IC, they are fried...
Now the bad news. These chips are not the usual TTL chips, but the very old, and obsolete DTL type. you neeed DTL, TTL won't work... You can probably find all the chips, as I did on ebay, but they are expensive. Second bad news, the PCB traces are VERY FRAGILE! No way to safely unsolder most of the digital IC without pcb damage. The only safe solution, using a very sharp tip cutter, cut the ic legs from the top, then gently, pull out each pin, one by one. Then using the desoldering pump, clean all the holes, install an IC socket and resolder at low temperature. Then insert the good IC.
As I said, no real point in testing at the start, you need to remove all the IC's... In my case I started from the left, clock oscillator, and move to the right of the schematic. So far i did about 4/5 of the board, testing it all the way according to the schematic voltages and waveforms, that are by the way quite accurate. Now my board is no longer toasting hot, and 5V supply current is almost back to normal.
I'm almost there and then I'll have a very nice, also recap digital board. But it is a long, delicate and somehow expensive job. AND you need to be able to work and test electronics, it is not an amateur job I'm afraid...
I'm away from home but I can post some reference readings once I'm back in October.
Once I'll be done with this repair, I think I'll install an overvoltage protection circuit into my turntable, on the 5V line (resetable fuse and transorb diode). I think that the original problem with this disaster is a defective power supply. If the 5v regulator is failed, it will passthrough the raw dc voltage before the regulator, that is sadly way over 5V, that in turn destroy the Digital board... Pitty there was no protection into the table itself, usually a good thing when you have a detachable external supply.
SB
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Thanks Algar_emi! That was quite detailed.
The links that Ralph provided in post 1135 have people using newer chips, unless I am mistaken.
This sounds like pretty difficult work. I am definitely an amateur and I have not done this level of surgery on an existing board. I'm sure I could do it given enough time and effort, but time is something I do not have at the moment. I do have a scope, and a desoldering hand pump, but no desoldering station or lab power supply. Apart from the desoldering station, I know how to use these tools, but I am not super skilled in desoldering several parts from a delicate PCB. I am also not an electronics technician, though again, given enough time I'm sure I can work my way through these circuits.
Can I send this board to you Algar, or Ralph, or Dave? Seriously. Are there places where you could potentially buy these boards whole from discarded tables?
The links that Ralph provided in post 1135 have people using newer chips, unless I am mistaken.
This sounds like pretty difficult work. I am definitely an amateur and I have not done this level of surgery on an existing board. I'm sure I could do it given enough time and effort, but time is something I do not have at the moment. I do have a scope, and a desoldering hand pump, but no desoldering station or lab power supply. Apart from the desoldering station, I know how to use these tools, but I am not super skilled in desoldering several parts from a delicate PCB. I am also not an electronics technician, though again, given enough time I'm sure I can work my way through these circuits.
Can I send this board to you Algar, or Ralph, or Dave? Seriously. Are there places where you could potentially buy these boards whole from discarded tables?