VM1000 Replacement Chips

[walkman]

Originally Posted by Omega232Devils

John,
Glad you solved your problem. I am sure Reggie would have helped if he were not on vacation.

Do you have more information on what you were seeing that made you suspect the IC chips? Are they individual chips for each indicator? I have fluctuating fuel flow indications. I have replaced the fuel flow meter with the newer style that is suppose to be more accurate, but it is not. Generally ranges about 2-3gal per fill up off. Or about 0.8gal/hr more than it actually burns.

Thanks,

Dan

Dan mine is off by that amount at fill up, or roughly 5-8% burn. I think it might be typical. Wish there was a k factor adjustment.

[Omega232Devils]

I would think the same thing, but my old fuel flow meter was accurate to within 0.1gal at fill up regularly.

At least it is inaccurate on the safe side as there is always more fuel than the quantity gauge indicates.

Dan

[johnp19]

Dan,

I had problems with MAP, fuel flow and oil pressure. The readings would fluctuate or stop working altogether. In the case of the oil pressure it would often read 20 or more pounds low. I plumbed in a mechanical gage and used pneumatic pressure to help work the problem. After trouble shooting the wiring, d-sub connectors, transducers, ground, board solder joints, changing out the onboard battery, etc I decided to swap out the three processor IC's on the analog board. These IC's are in sockets which makes the process fairly easy. I highly recommend the right tools for working with these IC's, especially for removal.

Just prior to swapping the IC's I suddenly lost pretty much every indication except for EGT and CHT. As soon as I swapped the IC's around I regained all indications but now did not have EGT and CHT indications. Based on this I ordered the new IC's from Digi-Key. I replaced the two IC's that appeared to have traces running back to the EGT and CHT inputs and now everything is working.

The point I take from this is that the IC's can apparently fail intermittently, or in the case of my oil pressure only partially fail.

I hope this helps,

John

[walkman]

Originally Posted by Omega232Devils

I would think the same thing, but my old fuel flow meter was accurate to within 0.1gal at fill up regularly.

At least it is inaccurate on the safe side as there is always more fuel than the quantity gauge indicates.

Dan

I meant, typical for the VM1000. I've had an EI gauge, which was usually accurate to with .1-.2 gal and a GRT HXr which was almost as accurate.

[Glas467]

I am back from vacation, good to see VMS discussion is still going strong!

FYI, bus control (or signal processing or A/D ... all names are synonymous with the same component) chip replacement is the second most common repair I do. In my article "Brains, Batteries, and Busses" http://eaaforums.org/showthread.php?...ies-amp-Busses
part of what I discuss is the analog board and the bus chips. The bus chips are the first processing component in the DPU to encounter the raw analog signal coming from the various sensors and transducers. As such, they are the most suseptable to voltage spike damage (static discharge, starter kickback, intermittant shorts, etc). It is possible for only one or a couple of channels on the bus to be damaged, in this case for example you may have one cylinder where the EGT graph is blank but all others work fine.

When replacing these chips, its important to match the original component as closely as possible. In the case of the bus chips, older (screw terminal type) DPUs use a different chip than the later serial type DPUs. As one poster from above noted, in the case of the serial DPU, exact replacements may not be readily available (I maintain a stock of the correct chips) from the common electronics shops like Digikey or Mouser. For this case it was critically important to get a chip rated for the same or lower amperage draw which the individual did.

The other recommendation I have is to make sure you have the right tools and equipment to do the job. i have lost count of the number of repairs I have done for folks who tried to DITY and damaged their DPU worse either from static discharge (they did not have a static free workstation and/or failed to take static precautions) or from using a hardware store soldering iron on an IC and ruining it and/or burning up the copper etching on the PC board.

Quick note also on the fuel flow accuracy issue ... FYI my EPI-800 totalizer is typically within 0.1 - 0.3 gal of actual fuel at fillup, it has never been more than 0.7 gal off so the EPI-800 and VM1000 systems are fully capable of very accurate fuel computing based on flow. Errors come into play from 3 sources 1) air bubbles or excessive turbulence in the fuel system 2) K factor variations 3) Power or signal interruptions.

Here I will address K factor variations ... for carb engines, FloScan manufactured the model 264 with an integral pulse damper in the unit with a K factor approx 47k (I dont have the tech specs in front of me so I am typing from feeble memory) ... Production ceased on this unit and the replacement is the 201B-9 with an external pulse damper and K factor approx 44.7k ... So you do the math and see that from the get go you have a 4.9% error when you replace a 264 with a new 201B-9. The newer serial type DPUs with software rev 2.0 and higher have a K factor adjustment feature, older DPUs do not and cannot be upgraded.

All the best,
Reggie