MC2100LT Speed increases randomly with stable PWM input

Thread Starter

BobRF

Joined Dec 16, 2022
7
Looking at a MC2100LT motor control board out of a Proform / Icron treadmill. The controller, from time to time , inexplicably , and dangerously surges or decreases the motor speed. Removed controller and motor from treadmill and placed on a workbench in my lab. Used a PWM controller ( 20Hz/18%.. ) to bypass the console input and have added a series resistor ( 480 ohms ) to the PWM input to the FD817 optocoupler to respect the data sheet. I have a 2 channel scope ( 222 )( ground isolated ) and DMM to check most of the likely places of reported issues. Motor controller comes up from soft start fine, runs at speed, varies with the change in PWM percentage input. After a few minutes it will suddenly increase the pulse width to the MOSfet driver with the same input PWM on the input ( pin 4 - HD2 ) . This also can occur right after powering up the board. Pretty much with the wealth of information provide on the MC2100 threads, I have found nothing out of order, Voltage regulators on the money, SCR motor pos voltage seems stable while running, so it comes down to what I believe to be the micro, which is outputting the PWM signal to the MOSfet driver. While there is some documentation on the reverse engineered schematic and MC2100/MC2100E motor control document posted, It is unclear to me what is affecting the micro to vary the PWM signal in this way. Has anyone seemed the same thing on a MC2100 ?
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
Don't remember seeing that issue, but could it be the FD817 itself?
There is also a small calibration pot on the HD2 end of the board that may give a similar effect if defective?
 

Thread Starter

BobRF

Joined Dec 16, 2022
7
Thanks MaxHeadRoom. I'll double check those items. I'm pretty sure I scoped the output of the F817 at the emitter side, but will recheck. The Cal pot seems to be an analog input to the micro.. I check it again to be sure it is going to the Floating 5, ground and the wiper has a stable voltage on it. Thanks again. Cheers,
 

Thread Starter

BobRF

Joined Dec 16, 2022
7
Back again and thanks... I did rechecked the F817 emitter side, nice stable PCM signal from the opto coupler that reflects the test PCM input to the Led. Checked the Cal pot and it has the+5V F rail, gnd and wiper can be moved with a range of voltages, currently set for 3.6 Volts. I did adjust it while the unit was operating and really had no effect on anything that I noticed. The treadmill this was in had no TACH reed input ( F/W most likely will ignore ) so there is nothing going it o HD7. So just to be safe I put a 100K across the pins to attempt to remove noise from the picture. This made no difference. Being the Micro has so many inputs to it from various sense points, I'm starting to wonder if a issued with one of these inputs from the motor voltage or current sense. I'll look closer at these areas, maybe it is an RC thing and there is a bad cap or something. Thanks again for your help.
 

Thread Starter

BobRF

Joined Dec 16, 2022
7
With the time available to me, I did a fair amount of checking in the areas of motor sense, etc.for obvious issues. No dice. I decided to get the old freeze spray out to see if I had a issue that could be made to happen with changes in temperature. It did. I think that I have isolated it down to C20, a 100 ufd on the silkscreen on my PCB, possibly C17 on the reverse eng'd schematic. This definitely speeds up the motor, which to me It doesn't make sense, in that this cap and a parallel .01 ufd smd seemed to only provide a bypass for the rail of the MIC4227 MOSfet driver. With that said, I'm still mot sure what is going on here. I'll monitor the pre-regulator voltage from the bridge input circuit ( before Reg1 ) while doing the freeze thing to see if the cap is loading this rail down. Something still bothers me about the U8's grounding arrangement with the .01 ohm tied to the pin 3 of U8 the low side driver, the source pin of the MOSfet and the 10K, 4.7 ufd going to pin 4 of the micro. The PCB I have has not been the most friendly to tracing with its thick solder mask applied. I will report back. Any comments will be appreciated. Cheers..
 

Thread Starter

BobRF

Joined Dec 16, 2022
7
To anyone still interested, I spent some more time with the MC2100LT board, to no avail.. Still temperature sensitive ( cold spray ) in the area of what the schematic calls out as C16. The Micro is definitely thinking it needs to increase the pulse width with drop in temperature in that area . Unfortunately, I Will have to defer any further time spent on it for a few days to work on other more pressing projects. The dang circuit, the current sense , is still not making sense to me. I would give my eye teeth to get a hold of the source or object code for the Cypress part :-}}..
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
I would give my eye teeth to get a hold of the source or object code for the Cypress part :-}}..
I am not sure if it is locked by blowing the read fuse, but the fact that the chip has the 5 pin programming header present, may indicate it is readable??
 

Thread Starter

BobRF

Joined Dec 16, 2022
7
That's a thought.. I'll have to investigate the CY8CxXXX data sheet and figure out the read method. If I can pull out the hex then I'll need a disassembler. I think the Cypresss uses a MC8 8 bit processor so maybe there is something floating around to do this. When I get time I'll see if I can read the flash memory. Cheers
 

Thread Starter

BobRF

Joined Dec 16, 2022
7
I ran out of time on this investigation. Needed to make the MC2100 reliable and get the treadmilll backing service. While replacing the two caps on the motor sense to pin 4 of the micro made things a lot more stable, there is still some thermal drift that does cause some unexpected variation in the motor speed. With that said I was able to find a used out of a working treadmill ( motor NG ) inexpensive MC2100LT on Ebay and it was plug and play. I will revisit this MC2100 in the future to see if I can understand the cause of the instability. Cheers
 
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