This unit presented with a broken cover down switch lever. It has other issues.
Power is good, clean with a scope. The turntable motor spins if I force it on by grounding the base on Q102 (motor run). The CPU clock (MN1421FPB) is running in the right range, strobe signals where they should be. I can't find a data sheet on that chip to show me any signals that put it in reset or some halt mode. The tonearm motor returns properly automatically if I rotate it out and turn the unit on.
I hate logic issues without enough clear documentation. I have the manual. Any pointers would be very helpful.
Thanks, Chris
Power is good, clean with a scope. The turntable motor spins if I force it on by grounding the base on Q102 (motor run). The CPU clock (MN1421FPB) is running in the right range, strobe signals where they should be. I can't find a data sheet on that chip to show me any signals that put it in reset or some halt mode. The tonearm motor returns properly automatically if I rotate it out and turn the unit on.
I hate logic issues without enough clear documentation. I have the manual. Any pointers would be very helpful.
Thanks, Chris
Hi, apologies in advance if you have already considered what I have to say. I'm making no assumptions (best starting point for troubleshooting).
Background: I have rebuilt and serviced about 10 Technics compact DD turntables (SL-5/SL-Q5/SL-Q6) and have never had a problem with the main PCB. I also have about a dozen of the motor units from these turntables that I have bought as parts (I repurpose them) and I have never found one with a faulty microprocessor.
Have you fixed the lid switch? The motor will not run if the lid switch is open.
Have you done the "measurements and adjustments" per the service manual? I always start with the calibration of the turntable as if any of the tonearm sensors are not calibrated correctly then strange things can happen.
Does the motor (when you force it to) run at the correct speed?
Cheers, Mike
Background: I have rebuilt and serviced about 10 Technics compact DD turntables (SL-5/SL-Q5/SL-Q6) and have never had a problem with the main PCB. I also have about a dozen of the motor units from these turntables that I have bought as parts (I repurpose them) and I have never found one with a faulty microprocessor.
Have you fixed the lid switch? The motor will not run if the lid switch is open.
Have you done the "measurements and adjustments" per the service manual? I always start with the calibration of the turntable as if any of the tonearm sensors are not calibrated correctly then strange things can happen.
Does the motor (when you force it to) run at the correct speed?
Cheers, Mike
Hi Mike,
Thank you!
The simplest suggestion can point to something I forgot, so thanks. I do the same thing. Your experience is valuable.
Yes, I fixed and verified the lid switch. This was the first thing I noticed. I glued a metal tag to replace what I think is a broken lever. I have no idea what the original looked like, but it now works. Also cleaned the switch (open when lid down).
Good point. No, I noticed that the "repeat" lamp didn't illuminate and looked at the processor after checking the power supply voltages and reset. The tone arm does return and stop if I take it out of the rest position. I assumed that meant the sensors were working there. I didn't run through the adjustment procedure as I feel I am dealing with a processor stuck in a state where it doesn't detect an album. I don't know what it normally does when you first hit play. This one does zero. I can see a red LED on up by the arm. Probably for tracking error. I'll wait for your response before diving into that. I did take the record detect lever out and made sure it wasn't damaged, then reinstalled it.
The motor runs smoothly when forced on. The waveforms look like the speed is hunting a bit, but a smooth rise and fall. The CPU clock is steady, slightly high.
I typically try to solve major faults before adjusting anything.
- Chris
Thank you!
The simplest suggestion can point to something I forgot, so thanks. I do the same thing. Your experience is valuable.
Yes, I fixed and verified the lid switch. This was the first thing I noticed. I glued a metal tag to replace what I think is a broken lever. I have no idea what the original looked like, but it now works. Also cleaned the switch (open when lid down).
Good point. No, I noticed that the "repeat" lamp didn't illuminate and looked at the processor after checking the power supply voltages and reset. The tone arm does return and stop if I take it out of the rest position. I assumed that meant the sensors were working there. I didn't run through the adjustment procedure as I feel I am dealing with a processor stuck in a state where it doesn't detect an album. I don't know what it normally does when you first hit play. This one does zero. I can see a red LED on up by the arm. Probably for tracking error. I'll wait for your response before diving into that. I did take the record detect lever out and made sure it wasn't damaged, then reinstalled it.
The motor runs smoothly when forced on. The waveforms look like the speed is hunting a bit, but a smooth rise and fall. The CPU clock is steady, slightly high.
I typically try to solve major faults before adjusting anything.
- Chris
Yep I haven't yet found an "easy" replacement for the lid switch but fortunately have always found all the broken parts and developed a repair technique. Sounds like you have successfully done the same!
I do remember that if the tonearm cover under the lid isn't installed correctly that you can have problems with the record detect switch. Sometimes this can result in the lid not closing properly or a broken record detect switch.
I usually remove the perspex lid (dust cover) per the manual so that you have better access to switches and sensors - and you can see what the tonearm is actually doing. The tonearm sensors have multiple functions so don't assume that all is OK there.
I would remove the dust cover and carry out the tonearm calibration. It is possible that the motor won't run unless the tonearm is within the tolerable error angle. You can visually check this with the dust cover removed.
The repeat lamp not illuminating is often a dirty switch - liberal amounts of Caig DeOxit usually works wonders.
Good luck!
Mike
I do remember that if the tonearm cover under the lid isn't installed correctly that you can have problems with the record detect switch. Sometimes this can result in the lid not closing properly or a broken record detect switch.
I usually remove the perspex lid (dust cover) per the manual so that you have better access to switches and sensors - and you can see what the tonearm is actually doing. The tonearm sensors have multiple functions so don't assume that all is OK there.
I would remove the dust cover and carry out the tonearm calibration. It is possible that the motor won't run unless the tonearm is within the tolerable error angle. You can visually check this with the dust cover removed.
The repeat lamp not illuminating is often a dirty switch - liberal amounts of Caig DeOxit usually works wonders.
Good luck!
Mike
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By the way, the cabinet lid switch (S702) should be closed when the lid is down.
It is common to damage the switch when removing it and reinstalling it - there is a note in the manual that says the switch must only be removed and reinstalled with the lid open.
If it is installed with the lid closed the it will be damaged the first time the lid is opened.
I would bridge out the lid switch temporarily and see what happens.
Oh, and forget what I said about the record detector switch - I don't have an actual SL-5 on hand and was looking at one of my SL-Q5 instead (which has a different method of detecting the record).
It is common to damage the switch when removing it and reinstalling it - there is a note in the manual that says the switch must only be removed and reinstalled with the lid open.
If it is installed with the lid closed the it will be damaged the first time the lid is opened.
I would bridge out the lid switch temporarily and see what happens.
Oh, and forget what I said about the record detector switch - I don't have an actual SL-5 on hand and was looking at one of my SL-Q5 instead (which has a different method of detecting the record).
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Hi Mike,
Thank you. I did set the CPU clock frequency, most signals look normal.
At the moment it looks like the CPU thinks the lid is either open, or no record is placed on the table. It doesn't matter whether the lid is up or down, exactly the same indications. The lid state signal is reaching the CPU.
I have operated the lid switch manually, no changes. Wish I had a working one I could compare states and signals to.
Thank you. I did set the CPU clock frequency, most signals look normal.
At the moment it looks like the CPU thinks the lid is either open, or no record is placed on the table. It doesn't matter whether the lid is up or down, exactly the same indications. The lid state signal is reaching the CPU.
I have operated the lid switch manually, no changes. Wish I had a working one I could compare states and signals to.
Hi Chris,
My money is still on the lid switch, short it out and see what happens?
(without a record on the table it should still spin a couple of times and then stop, so I don't think it is the record switch)
My money is still on the lid switch, short it out and see what happens?
(without a record on the table it should still spin a couple of times and then stop, so I don't think it is the record switch)
Hi Mike,
Hmmm, did that before I repaired the switch. I even measured the voltage open and closed to make sure it was actually making good contact (I had to clean it).
I thought it should at least spin a little. It doesn't, the enable signal remains in stop mode. I checked the inverter transistor. If I desolder that pin on the CPU and short the trace, the motor runs. So that information helps me Mike.
Hmmm, did that before I repaired the switch. I even measured the voltage open and closed to make sure it was actually making good contact (I had to clean it).
I thought it should at least spin a little. It doesn't, the enable signal remains in stop mode. I checked the inverter transistor. If I desolder that pin on the CPU and short the trace, the motor runs. So that information helps me Mike.
Puzzling! Ah well, process of elimination I guess.
At least you know there will be a good “Aha!” moment at the end of all this! 😁
At least you know there will be a good “Aha!” moment at the end of all this! 😁
lol!
Yes, for sure! I did find C304 (100uF 10VDC) with a badly corroded lead. I replaced it with a Poly-Aluminum since it filters the CPU supply. 20 VDC rating, I don't trust anything below 16 VDC. Didn't improve anything. This unit has some issue affecting the CPU that prevents it from allowing normal operation. I wonder if it has an AC detect? I'll go looking.
Techs get stuck on simple things they miss, or truly strange problems. A lack of complete information sometimes means it isn't worth learning everything about a unit. I am approaching that situation. If this wasn't for a very good friend, I would have dropped it a while ago.
Yes, for sure! I did find C304 (100uF 10VDC) with a badly corroded lead. I replaced it with a Poly-Aluminum since it filters the CPU supply. 20 VDC rating, I don't trust anything below 16 VDC. Didn't improve anything. This unit has some issue affecting the CPU that prevents it from allowing normal operation. I wonder if it has an AC detect? I'll go looking.
Techs get stuck on simple things they miss, or truly strange problems. A lack of complete information sometimes means it isn't worth learning everything about a unit. I am approaching that situation. If this wasn't for a very good friend, I would have dropped it a while ago.