I'm loving this series. The collaborative effort and feedback from other viewers and your ability to interpret the circuit design, explain what has gone wrong and what you think may have gone wrong together with minor circuit improvements along the way keeps me glued to the screen.
Glad to see you made good progress! The back EMF snubber diodes seem to be a great idea to prevent future issues with the IC11 chip, it's an inexpensive mod that should in no way affect any other functionality. My unit has one quirk when using the Leakage/Ohms function, as it seems to be accurate enough when set to leakage, but, when set to ohms, on anything fairly low in resistance it just displays "0 Ohms", but if measuring with the ESR function it gives a fairly accurate measurement comparable to the actual DC resistance. I noticed in the user and service manuals, that, there are no specs' as to the range of "Ohms" for the resistance measurement function, nor is there any mention of a specific cal procedure for the ohms measurement function, so, seeing that I have a bunch of ways to measure resistance, I am not going to sweat it.
Great progress! Just wanted to mention that an analog switch feeding a cap to ground followed by a voltage follower is a classic "sample and hold" circuit. This is grabbing the initial voltage across the cap due to the applied current, before it starts charging, which is how they measure the ESR.
Fantastic work and persistence, Tony. Definitely the relays needed back EMF protection for the drivers. It sounds like the MCU was exposed to electrical stress which caused its port outputs to fail. Given the number of other failures you have found, maybe that is not a surprise. Keep going, you will get there.
Take it easy Tony do what you got to do first... with that said I seen a few phillips chips in there .... check those as phillips was crap with making ic's very high failure rate... Love your video's always learn something so thank you for what you do .
Used to confuse the hell out of me when I was tinkering with 803x chips. PSEN is to select internal or external program memory, ALE is to enable the latch which demuxes the address/data bus for when you're using the external :)
Hi again Tony 9:30 careful now 74cxxx and 74hcxxx dont't have the same logic levels as I told you before. 74c= 0 max 1.5v, 74hct= 0 max 1.35v. It's not a lot; but it has hit me several times. Keep up the good work.
Excellent progress. The snubber diodes on the relays are a good idea, I'm surprised they weren't part of the original design. Seems like they were relying on the intrinsic diode in the MOSFETs to handle the back EMF. The lead short test failing is a good clue to resolving the ohms/esr problem. Regards, David
as the circuit is fairly dynamic, it will be hard to do solid measurements, I would suggest to use a 3 channel scope measurement on each of the reed relays, chan #1 on contact input, chan #2 on output of contact, chan #3 on coil to serve as trigger, then do a single shot measurement on relay activation and then see if the relay doesn't have any contact resistance which could be cause of your error 4, alternative way to measure relays static is to pull the mcu and put power on the output associated with te relay and measure it dc resistance, this may differ from the dynamic behaviour
Did you happen to clean those toggle switches on the front panel? Have chased my tail many times before and turned out to be poor contact on a switch... Good luck!
This machine is an early example of a MIXED analog-digital circuit design and all the problems associated with it. Without a proper description or block-diagram of the MCU control firmware it is going to be very difficult to repair. For obvious reasons, manufacturers never release firmware source code or specs to protect their IP
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I'm loving this series. The collaborative effort and feedback from other viewers and your ability to interpret the circuit design, explain what has gone wrong and what you think may have gone wrong together with minor circuit improvements along the way keeps me glued to the screen.
Glad to see you made good progress! The back EMF snubber diodes seem to be a great idea to prevent future issues with the IC11 chip, it's an inexpensive mod that should in no way affect any other functionality. My unit has one quirk when using the Leakage/Ohms function, as it seems to be accurate enough when set to leakage, but, when set to ohms, on anything fairly low in resistance it just displays "0 Ohms", but if measuring with the ESR function it gives a fairly accurate measurement comparable to the actual DC resistance. I noticed in the user and service manuals, that, there are no specs' as to the range of "Ohms" for the resistance measurement function, nor is there any mention of a specific cal procedure for the ohms measurement function, so, seeing that I have a bunch of ways to measure resistance, I am not going to sweat it.
The saga of the Sencore continues!
The unit could really stand to have a backlight for the LCD displays… or retrofit some 7-segment LED displays for better visibility.
Wonderful content…it ‘s like binge watching a Netflix series
Great progress! Just wanted to mention that an analog switch feeding a cap to ground followed by a voltage follower is a classic "sample and hold" circuit. This is grabbing the initial voltage across the cap due to the applied current, before it starts charging, which is how they measure the ESR.
Yes, very useful !
Fantastic work and persistence, Tony. Definitely the relays needed back EMF protection for the drivers. It sounds like the MCU was exposed to electrical stress which caused its port outputs to fail. Given the number of other failures you have found, maybe that is not a surprise. Keep going, you will get there.
Take it easy Tony do what you got to do first... with that said I seen a few phillips chips in there .... check those as phillips was crap with making ic's very high failure rate... Love your video's always learn something so thank you for what you do .
Great series. I will be referring to this a lot for my own repair. Thank you!
Used to confuse the hell out of me when I was tinkering with 803x chips.
PSEN is to select internal or external program memory, ALE is to enable the latch which demuxes the address/data bus for when you're using the external :)
Clean the fuse contacts behind the BNC connector. This can cause problems with lead zeroing
At first it seemed to me that I wanted such a device. But now I clearly understand that I DO NOT want 😁
Hi again Tony 9:30 careful now 74cxxx and 74hcxxx dont't have the same logic levels as I told you before. 74c= 0 max 1.5v, 74hct= 0 max 1.35v. It's not a lot; but it has hit me several times. Keep up the good work.
Excellent progress. The snubber diodes on the relays are a good idea, I'm surprised they weren't part of the original design. Seems like they were relying on the intrinsic diode in the MOSFETs to handle the back EMF. The lead short test failing is a good clue to resolving the ohms/esr problem. Regards, David
Didn't those relays have a LED attached when you got the unit? Maybe that was an EMF mod.
Back emf diodes are hooked up in reverse with respect to the coil. LED indicators were same polarity.
When you do get it completely working, you can add some lighting to those LCD's as the frosting on the cake. 👍
as the circuit is fairly dynamic, it will be hard to do solid measurements, I would suggest to use a 3 channel scope measurement on each of the reed relays, chan #1 on contact input, chan #2 on output of contact, chan #3 on coil to serve as trigger, then do a single shot measurement on relay activation and then see if the relay doesn't have any contact resistance which could be cause of your error 4, alternative way to measure relays static is to pull the mcu and put power on the output associated with te relay and measure it dc resistance, this may differ from the dynamic behaviour
Excellent. Do you keep field notes? Handy for remembering where you left off...
Did you happen to clean those toggle switches on the front panel? Have chased my tail many times before and turned out to be poor contact on a switch... Good luck!
Cheers !
I remember Sencore had a problem with those and the replaced mine with the 103
This machine is an early example of a MIXED analog-digital circuit design and all the problems associated with it. Without a proper description or block-diagram of the MCU control firmware it is going to be very difficult to repair. For obvious reasons, manufacturers never release firmware source code or specs to protect their IP
Hi everybody
The Error 4 turn out to be a dirty contact on the white relay. Look at the email I sent you. Hopefully that will cure that problem.
Jay
Hi Tony, did you go for the 17 release version of the EPROM in this video. Did you try the old 13 release version with the new microprocessor ?
It is currently running on V17. I also tested it on V15 and it seemed to work as well. I could not tell any difference between the two.
I don’t know this machine, but don’t you have to select a capacitor type with the buttons on the left? Maybe those are used for ESR or leakage tests?
Back on track! I can wait for when you have more time. Nice work, enjoyed;thanks.