m22 room temp display

[ruggy]

I'm new to the sight and you guys seem to have the info I'm looking for. My heater failed last winter in Maine and the pipes froze.(-31deg.) I replaced the mat and all necessary gaskets. The room temp. display is erratic. It may say 45 and fly up to 84 and in a split second drop down to any temp in between. So the burner doesn't have a clue on how it should act. Also the flame is perfect on low and med. burn but, on high burn it flashes every few seconds. As far as the temp issue; I've read the t'shooting charts. They ask if theres 2.8v @ TP4. Easy enough, I'm assuming neg. ground. Is this correct? Causes could be failure of R12, R13, C11, or microprocessor IC1. I can check and replace electronics. Where in the world or who in the world has the processor?
Any help or diretion on this would be MUCH apprecated, before it gets to cold.
Ruggy in Bridgton,ME

[HayZee518]

replace the temperature thermistor. this is giving you erroneous readings. when the connection is broken to the thermistor, the temp on the room temp goes down to 42 degrees. a loose connection will do it too!

[ruggy]

m22 temp display

thanks for the reply hayzee, What I failed to say is, that was the first thing I thought of and exchanged my thermistor with my neighbors and my temp display was still all over the place. Next, I will check the connections at the socket and go from there.

[HayZee518]

the m41 and m22 has a molex plug in back two wires from there go to the motherboard. the system defaults to 42 when there's an open thermistor or connection

[ruggy]

m22 room temp display

That's helpful info. The heater is in Maine and I won't be there for a couple of weeks. But I will trace the connections back to the mother board. With the thermistor unplugged, it will hold that default temp. 42deg. but, when I plug in the thermistor, as I said, It goes anywhere from 42 to 84 or anywhere in between. rapidly. Even with a different thermistor plugged in. Has to be a bad or loose connection. I'll let you know. thanx.

[HayZee518]

has to be a loose connection -or- the motherboard temperature section is on the way out. I hate to think the cost of a rebuilt mb from monitor products -if- they even make them anymore.

[adnadeau]

TP4 measurement

As near as I can tell from the schematic, TP measurements should be made to point EP which is the DC return. As far as IC1 goes, it's probably long out of production. The spec sheet on it implies it has some firmware burned in for specific OEM applications.
BTW, Thurlows in Bridgton will order parts for Monitors and Toyotomis.

[ruggy]

tp measurments

Thank you for the reply on the test point measurements. I will do some more snooping around inside the heater in a couple weeks. You've given me some good information.

[ruggy]

m22 room temp display erratic

has to be a loose connection -or- the motherboard temperature section is on the way out. I hate to think the cost of a rebuilt mb from monitor products -if- they even make them anymore.

Ok, so I ran the m22 all weekend with the cover off looking for loose or bad connections pertaining to the erratic temp display. nada! Voltage measurement taken at tp4 (5v) Flow chart states approx. 2.8v. Lable next to tp4 on circuit board says " tp4 5v". If that's not confusing enough, flow chart states, failure of r12 or r13 as possible cause. The schematic states the value of these resistors at 1k for r12 and r13 is illedgable. Measured value of these resistors is approx. 25k, and the code on both these resistors is 23k. Anyway, the heater ran fairly normal all weekend. I have a digi. thermometer on top of the heater for reference. The heater reading differed by 2 or 3 deg. hi or low. but didn't go squirrely like it had before. I'm replacing the thermistor for starters.
[IMG]file:///C:/Users/Bruce/AppData/Local/Temp/moz-screenshot-2.jpg[/IMG] [IMG]file:///C:/Users/Bruce/AppData/Local/Temp/moz-screenshot.jpg[/IMG][IMG]file:///C:/Users/Bruce/AppData/Local/Temp/moz-screenshot-1.jpg[/IMG]

[HayZee518]

mouser electronics in texas has thermistors. resistors probably have a 20% tolerance no band = 20%, silver = 10%, gold = 5%.
25K = RED, GREEN, ORANGE - 23K = RED, ORANGE, ORANGE
MPI says it is normal for the set point to be overshot by 2 or four degrees. the display will not show odd digits