Ford PSOM repair help

[Hornnumb2]

I am trying to figure this out, here is a diagram of the board.

  The part beside the mov fell off and one leg is broke off of it. I attached a pic but need help identifying it. The voltages on the transistor are B-11.61, C-1.35 and E-12.14. I should have 9 volts on C right? Thanks

[LateLesley]

It's a tantalum capacitor I think, possibly C1 in the diagram.

it looks like it's 22uf 20V

You'll find one here - https://www.mouser.co.uk/Passive-Components/Capacitors/Tantalum-Capacitors/Tantalum-Capacitors-Solid-SMD/_/N-75hr4?keyword=226&No=575

They have 25V ones which would be suitable.

[Hornnumb2]

Would the 5101 transistors give the wrong reading on the collector because of faulty transistor or something  feeding it? Thanks

[LateLesley]

It's hard to tell, without knowing the test conditions. Transistors usually need about 0.6V between the base and emitter before they turn on (this is a very rough estimate, it varies from transistor to transistor, and it's really the current that is important, not the voltage, as they a current controlled devices) . so of NPN the base needs about 0.6V above the emitter, for PNP the base is 0.6V below the Emitter. Your test showed about a 0.5V difference, so the transistor might not have turned on (IE stayed high resistance), and led to the collector voltage being low.
Your diagram has voltages measured, some which look a little off, like real world values. But it doesn't say the test conditions, and you'd have to replicate the test conditions to get similar voltages.

Transistors usually fail short, or open. so either you'd measure all 3 legs as shorted together, or no "diode drop" in diode mode between the base emitter, and base collector. It depends on the failure mode. Try diode measurement on your meter, between the base emitter, and see if you get a reading of about 0.3V - 0.7V. It'll only work one way, the other should show open. (though this can be affected in circuit by other components).

[Hornnumb2]

Yes I get .5 one way and open the other. So it should be good, right?

[Hornnumb2]

Would this one work, https://www.ebay.com/itm/KEMET-T491D226M020AS-Tantalum-Capacitor-22uF-20V-20-2917-SMD-NEW-Qty-10/191513680636?epid=0&hash=item2c971adafc:g:iqwAAOSw7aBVJqMN

[fzabkar]

AISI, Q5 is the pass transistor in a 9V linear regulator. The control circuitry for the regulator is inside IC1 which clearly has additional functions.

For some reason, IC1 is not providing sufficient drive to the base of Q5. Could this chip be in standby mode? Is the PSOM module receiving all the correct external signals/voltages? Have you linked pins 1 and 3 (Battery and Run)?

IC1 appears to incorporate a second linear regulator with an output at pin 15. This is connected to Vcc (5V). However, I would first examine the board for other possible sources for Vcc.

[Hornnumb2]

Would the ebay capacitor work, then once I get it back on the board I can do some more checking. I am just feeding it on the bench with 12v on pin 1 and 3 and ground on pin 2.

[fzabkar]

Maybe IC1 gets an enable signal for the 9V regulator from IC4

The 9V rail appears to be required by IC5. It would be helpful to know what this IC does, then we could decide if it makes sense for it to be disabled when on the bench.

[fzabkar]

Would the ebay capacitor work, then once I get it back on the board I can do some more checking. I am just feeding it on the bench with 12v on pin 1 and 3 and ground on pin 2.

Yes, that should work, if it's not a fake.

https://media.digikey.com/pdf/Data%20Sheets/Kemet%20PDFs/T491.pdf

[Hornnumb2]

got cap back on board with no change,
pin 1 is 1.6
pin 16 is 1.3
pin 15 is .7
Could the ic be bad not passing the correct current? Thanks

[Hornnumb2]

here ic ic1

[fzabkar]

If the input to IC1 pin #6 is good, then I would think that IC1 is faulty. I suppose it would be prudent to replace Q5 just to be sure that it isn't the root cause. I suppose that the 5V supply would be derived from the 9V, so that would account for its absence.

70013FB is a FoMoCo internal part number. It may be a special function IC. AFAICT, the "FB" suffix denotes that this IC is a power chip of some kind, eg regulator, power supply supervisor.

Could we see the whole PCB? Both sides?

[Hornnumb2]

Pin 6 is at 7.6v. Thanks

[Hornnumb2]

here is the front

[Hornnumb2]

Here is the back

[fzabkar]

Other than changing Q5, ISTM that IC1 would be next choice.

If replacing Q5 doesn't solve the problem, then I suppose you could remove Q5 and inject a 9V supply into the IC's 9V pin. Of course you must wait for the 12V supply to appear before you inject 9V. If this fixes the problem, then that would confirm that this section of the IC is faulty, in which case you could add an external 9V regulator. I would choose a regulator with an enable pin so that the Run signal can control it (otherwise it would drain the battery). Of course, if you find a spare IC1, then go with that.

[Hornnumb2]

Would there be any crossover to work in the place of Q5, its a 5101FB but only place I can find it is in China. Thanks

[fzabkar]

Those 5nnnFB numbers are FoMoCo internal numbers. In the past I have replaced such transistors with off-the-shelf types (in other Ford products). Just find a regular PNP transistor with the same pinout (BCE) and package. I imagine that the current requirement wouldn't be too high.

Here is an original 5101FB (?)

https://articulo.mercadolibre.com.ar/MLA-610601827-5101-fb-5101-fb-5101fb-transistor-driver-to220-_JM

The specs of 450V, 4A, TO220 seem extremely excessive. 


Edit:

You might like to check the standard transistors that were available from Motorola in 1994:

http://www.bitsavers.org/components/motorola/_dataBooks/1994_Motorola_Semiconductor_Master_Selection_Guide.pdf

The MJE1123 on page 430 seems like a suitable candidate -- 40V, 4A, PNP, TO220AB, hfe = 45/100, Pd = 75W.

There should be better modern equivalents, though.


BTW, I'm still betting on IC1.

[Hornnumb2]

Other than changing Q5, ISTM that IC1 would be next choice.

If replacing Q5 doesn't solve the problem, then I suppose you could remove Q5 and inject a 9V supply into the IC's 9V pin. Of course you must wait for the 12V supply to appear before you inject 9V. If this fixes the problem, then that would confirm that this section of the IC is faulty, in which case you could add an external 9V regulator. I would choose a regulator with an enable pin so that the Run signal can control it (otherwise it would drain the battery). Of course, if you find a spare IC1, then go with that.

So if I remove Q5 and inject 9v on pin 16 right?  That should give me life if the IC1 is at fault. Thanks

[fzabkar]

I have no experience with this particular board, but that would be my guess. I would have hoped that someone else would have chimed in with their opinion, but it's your choice. Please don't blame me if it goes wrong. Wait for the 12V supply to come up before injecting 9V, if you intend to give it a go. Even if this works, be prepared for other things to be wrong with the chip.

[Hornnumb2]

Should I start with a lower voltage and work my way up to 9v?

[Hornnumb2]

Well replaced IC1 and Q5 and have the same results, any other ideas? Thanks

[whiteboarddev]

@Hornnumb2 Thanks for the schematic on this board. I just finished debugging mine and it turned out to be a failed solder joint at pin 7 at the main plug. The speedometer was working but the computer had a code for the VSS and intermittent hard shifting. After repairing the joint the truck runs great. I'm not sure what other common failures this board has. I wanted to post up how mine broke in hopes it helps someone in the future.