Tach stepper motor replacement info needed.

[Yeti_Owner]

Holy crap, I'm a moron, lol.

LD=Line Driver.

9638LDX is the one. Looks like it drives both the tach and the speedo.

CTS9645 is a analog to digital converter - odd, you think that it would be the other way around on analog gauges.. wonder what analog signal it's making digital for the dash?


Ok - now here is the $50 dollar question. Which resistors are different on the boards? One of them is going to be, and that resistor is the one we need to swap.

Anyone have a good photo of the frontside of a v6 tach cluster's circuitboard?

 

[great white]

Holy crap, I'm a moron, lol.

LD=Line Driver.

9638LDX is the one. Looks like it drives both the tach and the speedo.

CTS9645 is a analog to digital converter - odd, you think that it would be the other way around on analog gauges.. wonder what analog signal it's making digital for the dash?


Ok - now here is the $50 dollar question. Which resistors are different on the boards? One of them is going to be, and that resistor is the one we need to swap.

Anyone have a good photo of the frontside of a v6 tach cluster's circuitboard?

Working on the assumption you're correct; I'm going to guess the analog to digital is out to the PCM. Probably takes the PPM signal from the VSS and converts it to digital for the PCM.

Although, it would make more sense to design the PCM to take the vss ppm signal directly and convert it on board, so I may be way out in left field on that one....

 

[Yeti_Owner]

Working on the assumption you're correct; I'm going to guess the analog to digital is out to the PCM. Probably takes the PPM signal from the VSS and converts it to digital for the PCM.

Although, it would make more sense to design the PCM to take the vss ppm signal directly and convert it on board, so I may be way out in left field on that one....

It would, lol. Then again, didn't the older ones have a module outside of the PCM that did it? The VSS and the coil reference are pulses, the driver IC chips convert that to a solid state DC voltage to move the gauge motors. Maybe the VSS and Coil pulse are kind of sloppy, more sine than square wave, and that chip clips/cleans them into a pure digital pulse?

 

[great white]

It would, lol. Then again, didn't the older ones have a module outside of the PCM that did it? The VSS and the coil reference are pulses, the driver IC chips convert that to a solid state DC voltage to move the gauge motors. Maybe the VSS and Coil pulse are kind of sloppy, more sine than square wave, and that chip clips/cleans them into a pure digital pulse?

My diesel has a VSSB (DRAC in older trucks) because the PCM is setup differently than a gasser, but I believe the newer (96+) gassers do not have a separate VSSB. My understanding was the processing happens inside the PCM, but maybe it goes to the cluster first like the older trucks (88-91) that incorporate the DRAC in the cluster.

I'm off my familiar ground though when talking about the later gassers (96+) and I may not be correct....

*edit*

The grey matter just kicked in. 96+ trucks correct speedo in the PCM. It was that way when I swapped my 89 over to TPI, a vortec headed block, a vortec harness and a 411 PCM. No VSSB or DRAC. So I'm going to say the speedo signal is driven by the PCM on 96+ trucks.

I still used a drac in my 98 to drive the cruise and cluster though. It was a bit of a mutt....

 

[sewlow]

Wow! You guys are discussing stuff way over my pay grade!
Got some pix of this stuff & maybe a solution.
Here's the pix of the steppers.

Escalade stepper.

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V6 stepper.

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Escalade circuit board.

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V6 circuit board.

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As far as I can see, the steppers are the same. There are no numbers or any other markings on them.
The circuit boards 'look' the same, except for the numbers at the top.
The Escalade's number is, 16183928J
The V6's number is, 16183928E
The only dif.'s are the letters at the end.
So, my 'Q' is, seeing as the only visible differences I can see are the letters at the end of the numbers, do you think that swapping the gauge faces with the back piece that contains the circuit boards would be the solution. The circuit board, to my way of thinking, is the brains of the operation.
The one glitch in my theory. The circuit board posted by Dylan is for a V8 100mph Gauge cluster, & it's wearing the same number as my V6 cluster!
The Escalade cluster I have is a 120mph model!
Do you think that a swap of the circuit boards between the faces is too simple to work? The odds of that being the case would be too good to be true! Lol!

 

[great white]

Don't think swapping hte board will work.

Lots of different component number between the two boards. Since the circuit traces and resitors/caps/diodes all look to be the same, the difference is probably flashed on to one of those ships somewhere. The solution might be as simple as lifting a chip from the V6 board to the escalade's, but that's beyond what I can tell you over a web board and a couple pics.

You'll probably have an incorrect speedo or tach depending on which board you put on which face...

 

[Yeti_Owner]

I'll check it when I get back at work. I'm more interested in the ohms on the resistors.

 

[great white]

I'll check it when I get back at work. I'm more interested in the ohms on the resistors.

Quick gander at the pics looks like they're the same banding code....unless you mean the SMT ones on the back.

 

[Yeti_Owner]

Bingo - different uni-d Resistor (or is it a diode? hard to see), one driver chip is different. The others have different identifiers, but that's ok, they are different manufacturers.

Try these:

Swap the logic boards, plug it in. It can't hurt to try, lol.

You should be good to go.

Edited: Actually, if that doesn't work, it's PCM based, and you're up the creek.

Could have saved me some time knowing you had both clusters, lmfao!!

 

[sewlow]

I have a re-programmer that I can use to recalibrate the speedo via the tire size input. I 'may' be able to do something with that. Maybe!
Thanks a bunch for all the input! Later tonight, I'll try the stupid simple approach first & see what happens when I swap the boards. Fingers crossed! Who knows! It may work! I'll post up the results!