Vision Micro Systems VM 1000

[Guest Terry Dactil]

Well, five years of perfect operation, then the VM100 system died when turned on.

 

The aircraft had been parked overnight in below freezing conditions for the first time, which I think was significant.

 

When power was switched on, at first there was some garbage on the screen, then it went completely blank. Nothing at all after that, even if power cycled off and on.

 

However, it was fairly easily fixed, so I thought I should publish this to add to our knowledge base in case someone else encounters the same problem.

 

Fortunately, having a spare DPU to swap components around soon showed that the problem was on the digital (upper) circuit board even though its 12v and 5v power supplies were quite OK.

 

Using my brute force and ignorance technique I tried exchanging one at a time

 

· EPROM (U4)

 

· TIMEKEEPER (U5)

 

· 8085 CPU (U1)

 

All to no avail. The fault remained, so it was time to get serious and bring out the big guns, i.e. an oscilloscope.

 

This showed that

 

· The CPU was in a 1 Hz reset loop. (pin 36 R̅E̅S̅E̅T̅ I̅N̅)

 

· The high order address lines on the bus (A8 to A15) were clean, and going from the 0v to the 5v rails.

 

· However, the low order address / data lines (AD0 to AD7) were a mess with bus contention. (This is where two signals fight over an output, one wanting high, and the other low. Most chips can pull down harder than they can pull up, so the chip wanting low wins and the result is a voltage down near the low rail, as shown by one of the address / data lines below).

 

 

OK. It looks like the program is crashing because of invalid data or addresses on the bus. First up, let’s see it I can find a rogue chip that is not obeying its chip select signal and waiting for its turn on the bus.

 

I removed the programmable array chip (U3) which controls the chip selection signals. This allowed me to manually enable/disable the other chips.

 

· U7, U8 and U9 all behaved perfectly. They were not the problem. I was starting to run out of ideas.

 

However, while poking around all the chips and flexing the circuit board to try and find a broken track, I discovered that applying a clockwise torque to the EPROM (U4) caused everything to return to normal.

 

· After cleaning and straightening the pins on the EPROM and its socket everything worked perfectly again.

 

I suspect that the cause goes back to the fact that the EPROM chip had been removed and inserted in its socket many times and this reduced the contact pressure on its pins in the socket. With the temperature change causing mechanical contraction and expansion, this was enough to break one or more of the socket connections and crash the system. This just confirms that the connectors are a weak point in electronics.

 

Subsequent operation has been normal, so I think I can say problem fixed.

 

Case closed.

 

 

[LN-FRV]

Terry,

 

My name is Harald Roen from Norway. I have just flown my RV-8 with a FADEC controlled IOF-360 A1B6 using the Vision VM1000FX as a engine monitoring system. I had a JPI engineer making me a PROM with the fuel and engine parameter on. When I installed it, the fuel tot. gage shows the numerical value "03" on both tanks when they are full. When they starts to be empty, it suddenly shows the value "02" and then it trigger the fuel low alarm on the EC-100. I have the short capacitive fuel probes installed, so when we where calibrating the probes it showed full when we got 17 gal into the tanks. I have two 21 gal tanks in the RV. It seems to be indicating the correct graphical and numerical values when empty, but not in between.

 

I also have a problem with the fuel flow transducer. I got information from VMS Techsupport in 2006 that I should connect as follows:

 

P1 connector:

 

Pin 2 Red

 

Pin 3 Black

 

Pin 14 White

 

It does not work........argghhhhhh.

 

I would very much appreciate your help or advise.

 

Bstrg

 

Harald.

 

It does fly like a rocket though :)

 

 

[BobVZ]

How's this for resurrecting an old thread. Any change of getting a copy of that IO360 eprom image? I have a VM1000 programmed for a V12, of all things, and would like to repurpose it for my 360.

 

Thanks,

 

Bob