This Tuner is an integral part of my Mum's system.
It has stopped responding to most of the buttons.
Free download pioneer fx 88 zl service manual
From the schematic, the buttons, all tactile switches not capacitive, all connect to the micro-controller.
I suspect the limit of my ability will be to ensure the mcu is receiving +5V.
Is there anything else I can possibly test for?
When on a station it appears to work perfectly.
It has stopped responding to most of the buttons.
Free download pioneer fx 88 zl service manual
From the schematic, the buttons, all tactile switches not capacitive, all connect to the micro-controller.
I suspect the limit of my ability will be to ensure the mcu is receiving +5V.
Is there anything else I can possibly test for?
When on a station it appears to work perfectly.
Make sure no switches are stuck on or are leaky and so shorting out the 'keyscan' from the uP.
Look for any backup caps that may have deteriorated. Sometimes removing any all time 5v backup cap and shorting the main uP can fix issues of a uP that is stuck in a loop. Make sure all power is off (mains plug removed) before doing that.
Look for any backup caps that may have deteriorated. Sometimes removing any all time 5v backup cap and shorting the main uP can fix issues of a uP that is stuck in a loop. Make sure all power is off (mains plug removed) before doing that.
Thanks.
Seems to respond to same 5 or 6 switches but none of the remainder.
I read 4.4V on the 5V test point.
Is that the sort of low volts that could cause these symptoms?
There are only 3 elcos around the 12 to 5V regulator transistor & one around the reset circuit (whatever that does). Plus a huge 22000μF backup cap, that works, as V remains for at least a couple of minutes after removal of power.
If it seems a sensible plan I might as well replace the 4 elcos (I think I can do from stock parts).
I could remove the backup cap if that might be the problem. I could fit a temporary 1000μF from stock if necessary.
Seems to respond to same 5 or 6 switches but none of the remainder.
I read 4.4V on the 5V test point.
Is that the sort of low volts that could cause these symptoms?
There are only 3 elcos around the 12 to 5V regulator transistor & one around the reset circuit (whatever that does). Plus a huge 22000μF backup cap, that works, as V remains for at least a couple of minutes after removal of power.
If it seems a sensible plan I might as well replace the 4 elcos (I think I can do from stock parts).
I could remove the backup cap if that might be the problem. I could fit a temporary 1000μF from stock if necessary.
I would have thought a backup cap should retain power for a lot longer tbh. Remember though that your meter is a drain. If you monitor the voltage you will see it fall. You have to come back a little while later and quickly connect the meter to see.
4.4v sounds slightly low. The Zener in the regulator is a 6V2 which should give about 5.6v on the emitter of the series pass transistor. D114 losses another 0.6v leaving about 5 volts. So you need to investigate that.
If in doubt over the cap then take it out as a test. It should all still work without it.
The same switches working could be a fault on a switch. There are two PCB's witch a couple more switches. Try disconnecting those. If you haven't a scope then you could try looking at the voltage between two of the keyscan lines in the matrix eg pin 64 and pin 40 and seeing if you detect any change in voltage (its not definitive without a scope) but if you do then it points to the switch working. You have to do that for all 4 lines (pins 64 to 61) and the inputs at pins 36 to 40. You are trying to see if any switch is leaky or short.
4.4v sounds slightly low. The Zener in the regulator is a 6V2 which should give about 5.6v on the emitter of the series pass transistor. D114 losses another 0.6v leaving about 5 volts. So you need to investigate that.
If in doubt over the cap then take it out as a test. It should all still work without it.
The same switches working could be a fault on a switch. There are two PCB's witch a couple more switches. Try disconnecting those. If you haven't a scope then you could try looking at the voltage between two of the keyscan lines in the matrix eg pin 64 and pin 40 and seeing if you detect any change in voltage (its not definitive without a scope) but if you do then it points to the switch working. You have to do that for all 4 lines (pins 64 to 61) and the inputs at pins 36 to 40. You are trying to see if any switch is leaky or short.
'At least a couple of minutes' meant that I hadn't tested over a longer period. As the voltage showed zero drop over this time then it bodes well for a much longer backup charge.
I actually do have a very underused scope.
If testing with a DMM, I test between pin & pin while operating the appropriate switch; eg pin 40 & 64 switch S101. Most easily done using the exposed switch pins.
If testing with a scope I would test each pin separately to ground?
Would it also be appropriate to put 5V from an external supply to TP33 and see if the correct voltage made a difference?
I actually do have a very underused scope.
If testing with a DMM, I test between pin & pin while operating the appropriate switch; eg pin 40 & 64 switch S101. Most easily done using the exposed switch pins.
If testing with a scope I would test each pin separately to ground?
Would it also be appropriate to put 5V from an external supply to TP33 and see if the correct voltage made a difference?
For the 5 volts I would say try and see why it is lower than expected. Look at the Zener voltage and the output of the reg and also the volt drop across the series diode in the 5v supply to the uP.
The Zener should have 6.2v across it, the emitter should be at about 5.6 volts and another 0.6 vlts should be lost across the diode leaving 5v for the uP.
Measure those voltages and see where it falls down.
Tact switches can in rare instances become leaky and that is very hard to spot. If you use a scope then make sure both lines on the uP have identical signals on them. These are probably not static voltages but will be a random looking pulse waveform.
The Zener should have 6.2v across it, the emitter should be at about 5.6 volts and another 0.6 vlts should be lost across the diode leaving 5v for the uP.
Measure those voltages and see where it falls down.
Tact switches can in rare instances become leaky and that is very hard to spot. If you use a scope then make sure both lines on the uP have identical signals on them. These are probably not static voltages but will be a random looking pulse waveform.
And use the scope to look at the rails. Maybe the input to the regulator has lots of ripple on it that a DVM might not resolve as being a problem.
OK, that's enough to be going on with.
One scope channel on each pin - I hadn't thought of that.
I am attempting to test independent of main unit with 12V smps.
It's a non-separate seperate.
Sits on top of main amp/cassette unit with ribbon umbilical.
I don't know what the AC supply or AC wave form shaping is/does and if it is essential to the operation.
One scope channel on each pin - I hadn't thought of that.
I am attempting to test independent of main unit with 12V smps.
It's a non-separate seperate.
Sits on top of main amp/cassette unit with ribbon umbilical.
I don't know what the AC supply or AC wave form shaping is/does and if it is essential to the operation.
The AC does look essential. It seems to go to the filaments on the VFD (vacuum fluorescent display) and also is used to tell the uP that AC is present.
In the meantime then I would discharge that backup cap (use a 100 to 1k) and then add a shorting link across the cap. Use a bit of tinfoil if you want to be quick.
Put a note on the unit as a reminder to remove it before powering up again...
Put a note on the unit as a reminder to remove it before powering up again...
Gosh! I can't believe I put this on the back burner since May!
Just got round to re-looking at it.
Sometimes the obvious faults are the correct ones.
Umpteen switches (at least 8) are not making contact when pressed, presumably oxidised. I suppose most never got used so were unnoticed until the couple of station switches that are used became faulty.
I am working on the hypothesis that replacement is the right medicine as I doubt any contact cleaner would actually get in and do any good.
Anyway, original Omron switches sourced from Ebay in the UK, straight and Right Angle, enough to do the lot. I just hope NOS switches are not also oxidised!
Just got round to re-looking at it.
Sometimes the obvious faults are the correct ones.
Umpteen switches (at least 8) are not making contact when pressed, presumably oxidised. I suppose most never got used so were unnoticed until the couple of station switches that are used became faulty.
I am working on the hypothesis that replacement is the right medicine as I doubt any contact cleaner would actually get in and do any good.
Anyway, original Omron switches sourced from Ebay in the UK, straight and Right Angle, enough to do the lot. I just hope NOS switches are not also oxidised!
That sounds like a good result. I guess they have all deteriorated fairly equally over the years... no idea why though.
An old fashioned kind of a fault 🙂
An old fashioned kind of a fault 🙂
Switches replaced.
Replaced the lot as they were sold in multiples of sufficient quantity.
Old style electronics - through hole parts & single side pcb.
Sometimes things pop in my head after the event and it occurred to me that the simplest way of testing would have been to solder a couple of flying leads to the pcb to clip a DMM or to short together to act as a switch.
Holding 2 test probes while operating the switch was near impossible.
This technique could be applied to many testing situations.
I bet the pro's do it all of the time. I bet lots of kit is damaged by amateurs like myself from slipping probes.
Replaced the lot as they were sold in multiples of sufficient quantity.
Old style electronics - through hole parts & single side pcb.
Sometimes things pop in my head after the event and it occurred to me that the simplest way of testing would have been to solder a couple of flying leads to the pcb to clip a DMM or to short together to act as a switch.
Holding 2 test probes while operating the switch was near impossible.
This technique could be applied to many testing situations.
I bet the pro's do it all of the time. I bet lots of kit is damaged by amateurs like myself from slipping probes.
Erm... well you do get used to holding two probes with one hand with practice but you need to be sure you won't damage anything with a slip. Stuff like 5 volt logic is pretty safe, its a bit more scary on a live SMPS 😉
Mini clip leads on either on the tact switches, or relevant solder pads works to confirm if they connect when activated.
Sometimes, Deoxit, carefully dribbled on the button area can seep down into the mechanism, and working the button helps clean the contacts.
Lord knows, I've had to replace hundreds of them over the years as well.
Sometimes, Deoxit, carefully dribbled on the button area can seep down into the mechanism, and working the button helps clean the contacts.
Lord knows, I've had to replace hundreds of them over the years as well.