So when the device runs, it stops working after maybe 10-30 minutes of use, beeps, flashes a red LED, and shows the error message "E76" on the LCD. Unplugging it & plugging it back in will get it to work for maybe 1-3 more minutes, then it fails again.
Attached is the error code from the service manual, as well as the relevant circuit shown in the service manual. I think the device is 10+ years old (I bought it off ebay), it is a discontinued model. Interesting that the service manual for this error code says to replace the entire PCB for the "failed" battery, when the replacement PCB retails over $1000!
Also attached are some relevant excerpts from the AT91M55800A datasheet.
The coin cell battery measures 2.83V, and it should work for the AT91M55800A all the way down to 1.8V.
I think either C10, C11, or R32 are not working? Maybe the circuit is designed to fail this way? I am no expert, I can read these datasheets but I am very novice with circuitry. Can you help direct me at what to test/replace?
R32 measures 0.99MOhm.
C10 no resistance reading (over 2MOhm).
C11 measures 16.45kOhm. Capacitors shouldn't have resistance right?
When I measure voltage over either C10 or C11 it starts around 2.1V-1.8V and rapidly drops to 1.4V then slowly drops to 1.2V.
The coin cell battery has two electric welds holding it in place, I am reluctant to replace it because it should work.
NRSTBU activates low, and I think it is what drives that error message and stops the device from working. The use for the battery in this device is so that when the grid power goes off, it will alarm (wake the person up) in addition to stop blowing. NRSTBU appears to be used to detect when the battery is low.
I think either C10 or C11 is discharging faster than the current through R32 can charge them, thus NRSTBU lowers and activates?
Some datasheet links:
Atmel Arm Microcontroller AT91M55800A
BAT54
The service manual for this device (and dozens more CPAP machines) is on apneaboard.com, behind a registration wall and a maze of links. I believe I've attached everything necessary though. I think the standard warranty for CPAPs is 2 years, and many people buy them second hand out-of-warranty (including me, I can't afford $4000+ retail new machine & service).
Attached is the error code from the service manual, as well as the relevant circuit shown in the service manual. I think the device is 10+ years old (I bought it off ebay), it is a discontinued model. Interesting that the service manual for this error code says to replace the entire PCB for the "failed" battery, when the replacement PCB retails over $1000!
Also attached are some relevant excerpts from the AT91M55800A datasheet.
The coin cell battery measures 2.83V, and it should work for the AT91M55800A all the way down to 1.8V.
I think either C10, C11, or R32 are not working? Maybe the circuit is designed to fail this way? I am no expert, I can read these datasheets but I am very novice with circuitry. Can you help direct me at what to test/replace?
R32 measures 0.99MOhm.
C10 no resistance reading (over 2MOhm).
C11 measures 16.45kOhm. Capacitors shouldn't have resistance right?
When I measure voltage over either C10 or C11 it starts around 2.1V-1.8V and rapidly drops to 1.4V then slowly drops to 1.2V.
The coin cell battery has two electric welds holding it in place, I am reluctant to replace it because it should work.
NRSTBU activates low, and I think it is what drives that error message and stops the device from working. The use for the battery in this device is so that when the grid power goes off, it will alarm (wake the person up) in addition to stop blowing. NRSTBU appears to be used to detect when the battery is low.
I think either C10 or C11 is discharging faster than the current through R32 can charge them, thus NRSTBU lowers and activates?
Some datasheet links:
Atmel Arm Microcontroller AT91M55800A
BAT54
The service manual for this device (and dozens more CPAP machines) is on apneaboard.com, behind a registration wall and a maze of links. I believe I've attached everything necessary though. I think the standard warranty for CPAPs is 2 years, and many people buy them second hand out-of-warranty (including me, I can't afford $4000+ retail new machine & service).
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