digital dash trouble shooting questions on '85 GN

[Evans Ward]

Helping a friend work on his digital dash on his '85 GN. He has an intermittent cutting in and out on display of his MPH speedo reading. Other features work as intended on the read out. My question is regarding the black plug that the digital dash plugs into. This the the plug that comes throught the blue green circuit board piece that the tin plated ears from the module connect at. Should the black connector have two lock/ locator tabs at both the 12 and 6 o'clock positions to center it outward and level? Asking that as my friend's car only has the lower 6 o'clock lock tab present/ intact . We cleaned the fingers on the tin plated parts with a pencil eraser and did the same for the rear of the printed circuit board (after removal) with the copper contact areas. Used compressed air to blow out all the connectors too. Car still has the same problem after what we did and I'm wondering if he may have a bad VSS buffer? Next question is how to test for that? Thanks!

 

[GNVenom]

When you say the display cuts out, do you mean that it goes to zero, then back to the MPH, or does the display blank out completely, then back on?

 

[Evans Ward]

When you say the display cuts out, do you mean that it goes to zero, then back to the MPH, or does the display blank out completely, then back on?

The latter of the two scenarios John and just the MPH feature doing it. Just wondering if that if the connector at harness end is not level, would it contribute to this issue due to not having proper connectivity?

 

[GNVenom]

It's not the connector. That one self-aligns at an angle. It's the dimmer resistor for the MPH VFD on the display board. Read about it here:

http://www.installationinstructions.com/FYI/digitaldash.pdf

 

[Evans Ward]

It's not the connector. That one self-aligns at an angle. It's the dimmer resistor for the MPH VFD on the display board. Read about it here:

http://www.installationinstructions.com/FYI/digitaldash.pdf

Thanks John for offering up your help here. We've downloaded that article and have read it a few times. Thanks for the time you spent in authoring this and others which so many of us have used over the years. Can you tell us what VFD is an acronym for? What does the repair entail?

 

[GNVenom]

VFD = Vacuum Fluorescent Display. The readouts are actually vacuum tubes that are very fragile. They break if you exert too much force on the reset knob (usually the trip odometer) and aren't available from anywhere. So if you break one, you need to cannibalize a known good used dash for parts - gets very expensive at that point.

The repair involves removing the microprocessor chip and replacing it with a new one, programmed to display true MPH above 85. If you send us the complete cluster, we go thru the flex board, and add a VOLTS charge resistor right on the flex board along with normal repairs of the resistor traces and power supply if needed. We also go thru the lamps and replace non-functioning bulbs, which is very common on these dash clusters. Once it leaves our plant, the dash is completely reconditioned and ready to go.

The VOLTS resistor assures that your alternator will charge in the event of a burned-out bulb.

 

[Evans Ward]

VFD = Vacuum Fluorescent Display. The readouts are actually vacuum tubes that are very fragile. They break if you exert too much force on the reset knob (usually the trip odometer) and aren't available from anywhere. So if you break one, you need to cannibalize a known good used dash for parts - gets very expensive at that point.

The repair involves removing the microprocessor chip and replacing it with a new one, programmed to display true MPH above 85. If you send us the complete cluster, we go thru the flex board, and add a VOLTS charge resistor right on the flex board along with normal repairs of the resistor traces and power supply if needed. We also go thru the lamps and replace non-functioning bulbs, which is very common on these dash clusters. Once it leaves our plant, the dash is completely reconditioned and ready to go.

The VOLTS resistor assures that your alternator will charge in the event of a burned-out bulb.

That's great info and again, thanks John! I will pass this info along to Billy. He and his Dad may even see this as I directed them here (not sure if either is a member?) earlier today. I'm familiar with the volts resister from my analog dash in my '87 and problems with that circuit on my flex board from a few years ago. I actually had to find another flex board (make that 3 until I got a good one) as many of my copper ribbons traces had delaminated. Eric Fisher from this board was kind enough to help me out and sold me a super nice used one he had personally stored in his attic. I do know that Billy wants his '85 dash to function correctly and this is the only non-functioning thing on his pristine low mileage '85 GN! Have a Happy New Year John!