Psom circuit help

[Hornnumb2]

I am trying to figure out where I am losing voltage, the center pin (c) on transistor should be giving me 9v but I am only getting 1.3. Which goes to pin 16 on IC1. B on transistor is outputting 11.8 but I only get 1.7 on pin 1 of IC1. Thanks Michael

https://imgur.com/2pML3nc
IC1 is a Motorola 70013FB
I have replaced the IC and transistor with no change in symptoms.

[redwire]

Re: Psom circuit help

Did you connect IGN to +12V (conn pin 3) to turn on the module? Otherwise I think it stays asleep. IC1 pin 6 should have 7V then and see if 5V is also present.
Ford 1995 PSOM schematic
https://www.youtube.com/watch?v=vPbsvX2EIWc

[stj]

Re: Psom circuit help

what is this for?
i see it has an unmarked SPI device on the schematic, an eeprom??

[eccerr0r]

Re: Psom circuit help

programmable speedometer odometer module ... the EEPROM probably keeps the odometer reading.

Looks like Ford dropped the ball on design of the power of this board, seems the protection circuit was not properly designed. Still very odd why ford designed it the way that they did, but oh well...

[Hornnumb2]

Re: Psom circuit help

I purchase a working board with wrong mileage and MPH (80 Compared to 120)
Working board voltages on IC1
1) 11.67 16) 9.01
2) 12.29 15) 5.1
3) .005 14) 113mv
4) .005 13) .005
5) .005 12) .005
6) 7.85 11) 1.06
7) 5.02 10) 1.06
8) 4.33 9) 5.1

Non working

1) 1.75 16) 1.3
2) 12.3 15) .7
3) jumping 14) .7
4) .003 13) .003
5) .003 12) .003
6) 7.75 11) .85
7) .79 10) 333mv
8) 104mv 9) 139mv

[Hornnumb2]

Re: Psom circuit help

All parts in that video have been replaced also.

[Hornnumb2]

Re: Psom circuit help

If I transferred the eprom to working board any idea if it would correct the 2 different MPH?

[Hornnumb2]

Re: Psom circuit help

I am guessing the eprom is the 8 pin chip,
working boards number is:
B53AN
89 Ford
Psom.01

Non
B47AH
89 Ford
Psom.01

[sam_sam_sam]

Re: Psom circuit help

Are all of the other ic chip number same on each board and do they have the same exact configuration if they do you might be able to put your ic chip from your controller and put it in the other controller and it might work

[Hornnumb2]

Re: Psom circuit help

The only difference I see is there is an a adjustable pot on the original board. The working board is marked with an X.

[redwire]

Re: Psom circuit help

On the non-working board, there is no power making it to IC1 pin 2. Check diode D1 is open, or a bad trace/solder joint. You can beep it out with multimeter.

The EEPROM would store mileage and axle ratio/tire size. So swapping it would fix that. I would read the EEPROM contents in the interest of science.

[Hornnumb2]

Re: Psom circuit help

Pin 2 is showing 12v on both, is that the wrong pin?

[redwire]

Re: Psom circuit help

If IC1 pin 2 is at 12V, but non-working board pin 1 is 1.75v then the big transistor Q5 has open-circuit E-B junction. Sorry I got mixed up with your list of measurements.

[Hornnumb2]

Re: Psom circuit help

Could I have got a bad transistor, I do have one more that came from a different provider. They are 5101FB

[redwire]

Re: Psom circuit help

Transistor Q5 Ford 5101FB is a house-number. Ford has custom numbers and parts everywhere in this PSOM.
It should test as a PNP, not NPN. Pinout should be B-C-E and tab/heatsink is C.
There is some problem with it, I wonder if the parts you got are OK or fakes.

For a substitute I would use an 80-100V transistor (because of transients, even with MOV) tough such as D45H11, D45H11G, KSE45H11. 80V 10A.

[Hornnumb2]

Re: Psom circuit help

So would I be better off taking the transistor and ic off the working board and putting on the non working one. I added a socket on the ic so that wouldn't be to bad to do. Or just swap eprom (IC2) over to working one with out the pot. Thoughts?

[Hornnumb2]

Re: Psom circuit help

If IC1 pin 2 is at 12V, but non-working board pin 1 is 1.75v then the big transistor Q5 has open-circuit E-B junction. Sorry I got mixed up with your list of measurements.

I don't have it in front of me to verify till I go back to work Friday, but i have been studying the pics and it looks like the trace is broke in the lower left hand of the photo above the through hole that has some black around it.

[redwire]

Re: Psom circuit help

Use your multimeter to test the trace continuity, and also the E-B junction on the transistor Q5. The black corrosion is weird and might have etched the trace.

When I fix stuff I try to find the bad part because changing parts doesn't always work or can make it worse if a bad part kills new parts.

[RJARRRPCGP]

Re: Psom circuit help

Did you connect IGN to +12V (conn pin 3) to turn on the module? Otherwise I think it stays asleep. IC1 pin 6 should have 7V then and see if 5V is also present.
Ford 1995 PSOM schematic
https://www.youtube.com/watch?v=vPbsvX2EIWc

"666 Hz" -> LOL!

[Hornnumb2]

Re: Psom circuit help

Trace was broke, now the only voltage I am missing is 4.3v on IC1 at pin 8, currently 277mv. Any Clue