Already posted this in the massive SP10 tread but worried it may not get seen in a 146 page thread and have a customer who uses this professionally losing money on its "down time" so hoping for a quick-ish answer from a specialist on the SP10. If not OK then sorry mods just delete it.
Have a Mk2 in from a customer and its got me pulling my hair out! The service manual is about the most arcane document I've ever seen for a start... but I digress....
It is used almost all day every day apparently and left running continuously. The customer reported that when returning to the TT he found it had stopped rotating and noticed that the PSU was much warmer than normal.
When delivered to me and set up well lo and behold it worked perfectly... for about 10 mins then it simply stopped.
Seems to be that worst of all faults, probably an intermittent IC or transistor which is neither S/C or O/C.
Following the fault finding chart got me nowhere. Everything checks out as it should when going through the "platter fails to start" flow chart. This flow chart is incredibly misleading as many of the voltages it asks you to check in fact vary widely depending on platter position! It says A1 to 3 should be 23V DC but in fact they are the drives to the motor and go from around say 3V to 28V ish as the platter completes a rotation pushed by hand. The PSU, drive heatsink and even motor all get warm as they are sitting there with a load on them but "stalled". Yes the brake is not stuck on and works as it should!
If you manually push the platter it seems "to want to go" and sometimes will rotate a few turns on its own.
The PSU is fine and recently recapped and all voltages correct.
I presume there should be a permanent frequency presented to the phase comparator/control board for comparison with the FG signal but there is nothing but DC levels on its edge connector. The manual seems designed to protect Matshusitas IP rather than aid fault finding and I cannot find any reference to eg "the reference signal from the oscillator divider board enters the control board on pin E11..."
Also, what is the input to the drive board? It's not clear if there should be an AC signal which is the drive to the motor after being split into 3 phases or or if the drive board takes a DC level and speed is proportional to this?
"a2" looks like an input but the fault flow chart says this should simply be 22V DC, which it is. Is there a simple way of feeding a signal from a signal generator to the drive board as a mock drive signal just to see if it eliminates this board? Or alternatively a point which can be either grounded or have a specific DC level applied to do the same thing?
I've spent about 7 hours on it so far with no results other than everything checked so far looking fine other than a suspicion that I should be seeing waveforms on the PLL/control board but there are non. It doesn't help that the manual shows loads of waveforms which should be there WHEN THE PLATTER IS REVOLVING but as it's a closed loop system it's a fault finding nightmare! I repair hi fi for a living but it's decades since I last took on a DD TT and I took a chance in accepting the job that it would likely be something obvious like a faulty PSU or S/C output transistor etc but it was not to be and in fact it seems to have one of those faults from hell.... can't win 'em all eh...
Edit: The crystal oscillator works fine, a square wave which changes in frequency when 33, 45, 78 are selected is present at "P2". The 50KHz oscillator on the drive board is working and all the "feedback phases" from the "sensing/commutating coils" give a DC signal proportional to platter position as they should via their respective rectifiers etc. It just sits there pulling current but not commutating and very much "still life".
Have a Mk2 in from a customer and its got me pulling my hair out! The service manual is about the most arcane document I've ever seen for a start... but I digress....
It is used almost all day every day apparently and left running continuously. The customer reported that when returning to the TT he found it had stopped rotating and noticed that the PSU was much warmer than normal.
When delivered to me and set up well lo and behold it worked perfectly... for about 10 mins then it simply stopped.
Seems to be that worst of all faults, probably an intermittent IC or transistor which is neither S/C or O/C.
Following the fault finding chart got me nowhere. Everything checks out as it should when going through the "platter fails to start" flow chart. This flow chart is incredibly misleading as many of the voltages it asks you to check in fact vary widely depending on platter position! It says A1 to 3 should be 23V DC but in fact they are the drives to the motor and go from around say 3V to 28V ish as the platter completes a rotation pushed by hand. The PSU, drive heatsink and even motor all get warm as they are sitting there with a load on them but "stalled". Yes the brake is not stuck on and works as it should!
If you manually push the platter it seems "to want to go" and sometimes will rotate a few turns on its own.
The PSU is fine and recently recapped and all voltages correct.
I presume there should be a permanent frequency presented to the phase comparator/control board for comparison with the FG signal but there is nothing but DC levels on its edge connector. The manual seems designed to protect Matshusitas IP rather than aid fault finding and I cannot find any reference to eg "the reference signal from the oscillator divider board enters the control board on pin E11..."
Also, what is the input to the drive board? It's not clear if there should be an AC signal which is the drive to the motor after being split into 3 phases or or if the drive board takes a DC level and speed is proportional to this?
"a2" looks like an input but the fault flow chart says this should simply be 22V DC, which it is. Is there a simple way of feeding a signal from a signal generator to the drive board as a mock drive signal just to see if it eliminates this board? Or alternatively a point which can be either grounded or have a specific DC level applied to do the same thing?
I've spent about 7 hours on it so far with no results other than everything checked so far looking fine other than a suspicion that I should be seeing waveforms on the PLL/control board but there are non. It doesn't help that the manual shows loads of waveforms which should be there WHEN THE PLATTER IS REVOLVING but as it's a closed loop system it's a fault finding nightmare! I repair hi fi for a living but it's decades since I last took on a DD TT and I took a chance in accepting the job that it would likely be something obvious like a faulty PSU or S/C output transistor etc but it was not to be and in fact it seems to have one of those faults from hell.... can't win 'em all eh...
Edit: The crystal oscillator works fine, a square wave which changes in frequency when 33, 45, 78 are selected is present at "P2". The 50KHz oscillator on the drive board is working and all the "feedback phases" from the "sensing/commutating coils" give a DC signal proportional to platter position as they should via their respective rectifiers etc. It just sits there pulling current but not commutating and very much "still life".
