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the actual Meter Movement is not a Meter at all such as the D'Arsonval/Weston that most folks are used too.. it is a Stepper Motor and the back bearing pod is the damper..... so fluctuating movement is generally from Bad Filtering as this should be taken care of by the electronics.
So attempting to set the needle perfectly, I have a feeling those 2 little dots around zero have something to do with it. The needle driver does move when ignition gets turned on. I’ve got it to where it’s off maybe 1mph at 30, and maybe 2mph at 60+. Although I’m happy,
sidenote. While I was clocking the needle, I had the “cap” off the needle base. The needle was bouncing heavily at all speeds. Perhaps the bouncing speedo issue could be resolved by adding some weight (in the milligram range)....
That needle cap needs to be on to balance out the needle. It will bounce around as the truck moves.
The 2 little dots are some kinda of calibration when the speedometer was manufactured, there are two more points around the 55 to 60 on the dial I recall.
You can reset the lockout on the PSOM, but you will need to be able to read and rewrite the EEPROM on it. I unsolder the EEPROM to read/write it but others on here have used a special IC programming socket that clips over the EEPROM. As for changing mileage, you can copy that from one EEPROM to another but so far I havent figured out the encoding.
Originally Posted by lonewolf_
the actual Meter Movement is not a Meter at all such as the D'Arsonval/Weston that most folks are used too.. it is a Stepper Motor and the back bearing pod is the damper..... so fluctuating movement is generally from Bad Filtering as this should be taken care of by the electronics.
The meter movement on these speedometers are a sine/cosine driven meter. It is a magnet core mounted to needle with two windings at 90deg of each other. The PSOM micro sends out data to a driver IC that moves the meter. No stepper motors in the 92 to 96/7 trucks.
Ahhhh OK I can agree with that... I just called it a stepper due to lack of words
"The meter movement on these speedometers are a sine/cosine driven meter. It is a magnet core mounted to needle with two windings at 90deg of each other. The PSOM micro sends out data to a driver IC that moves the meter. No stepper motors in the 92 to 96/7 trucks."
I have never actually taken the Movement apart ... and I still wonder IF they in fact have Damping Fluid in the rear bearing Pod.
There have been several others who reversed these things over the years too .. the big issue is the Motorola IC's I can get sources for them BUT no data sheets other than the EEPROM itself.
I use an old Willem Programmer myself... works fine and mount a socket on the PCB for ease of swapping out the EEPROM.. I do have the Test clip with my programmer but I seldom use it
So I got the needle to read pretty close to dead nuts. Mileage is perfect. But I scooped that cluster with rpm gauge. So I swapped my PSOM with the newer face/motor assembly. Now it’s really dead-nuts.
Bonus is that a have fully functional cluster for sale now. I basically swapped a pretty close, for a dead-nuts model lol. Avoided having to pay to have mileage programmed. Only drawback, is I still only have one calibration left lol
P.S. That calibration count is ridiculous. I suppose there’s some limit before the chip runs out of memory. It’s probably not replacing the constant but adding a number and addressing a particular memory block.
