Testing PCB 70's Car Instrument Cluster

Thread Starter

GVPCB

Joined Nov 6, 2022
1
Hi,

Please be aware I am a bit of a noob when it comes to PCB's, electronic circuits... thanks for the patience in advance...

Over the past years I've collected a few instrument clusters from 70's Alfa Romeo Cars (different hobby ;-) ) Before reselling, I want to make sure the basics are working. All of these clusters have basically the same PCB in use. For now I only want to test if all instrument lights are working / coming up.

Please find picture attached, some basic questions:

(All lights basically work the same way, see picture for details)

1 I assumed taking a look at the patterns would tell me which Pin (3) would match with which light. I was able to get a few tested but majority failed.
2 This board seems to have 2 'grounds' ? Why would that be?
3 What would be the best approach to verify if all connections are still working?
4 General: Why are these patterns widening / narrowing (see 1 for example), a simple line would work as well?

(For now I am using a bulb I know is ok, just replacing the position every time)

Once again, thx for the patience/replies in advanceVintage PCB.png!

Vintage PCB.png
 

LowQCab

Joined Nov 6, 2012
2,650
Surface-Corrosion of the Printed-Circuit,
and the Plastic-Substrate starting to turn brittle,
are the 2 main problems You will see.

Usually, if the Plastic-Substrate is not cracked, you'll be ok with just
polishing the Copper to regain a clean connection.

Don't forget that the Bulb-Sockets can corrode as well.
You might solve this by replacing all the Bulb-Sockets with
aftermarket LED replacements.

Your Printed-Circuit, and Bulb-Sockets, look like the
exact same design that General-Motors was using during that era.
The Bulb-Sockets may interchange.
.
.
.
 

geekoftheweek

Joined Oct 6, 2013
916
1 I assumed taking a look at the patterns would tell me which Pin (3) would match with which light. I was able to get a few tested but majority failed.
2 This board seems to have 2 'grounds' ? Why would that be?
3 What would be the best approach to verify if all connections are still working?
4 General: Why are these patterns widening / narrowing (see 1 for example), a simple line would work as well?
1 - You should be able to trace from the pin to the light. If it doesn't seem to work right then I would suspect corrosion.
2 - It was probably just easier that way. Since the plastic sheets are a single layer circuit there probably wasn't any way to combine all the grounds into one pin. It may also be they needed to use two circuits to break up the combined current into manageable levels to not melt the plastic.
3 - The best would be to connect them as they normally would be used with lights and gauges installed. The gauges will take a few more parts and information to properly test, but simple potentiometers will work for fuel, temperature, oil pressure, and the like. You will just need to know what values match up with what resistance. RPM may be a bit of a challenge depending on it's internal circuitry. You may be able to get by with switching 12V on and off, but I would guess it would be more likely you would need something much higher to simulate the spike that happens on the "-" post of the coil during the ignition cycle.
4 - It's just a guess, but I'm thinking it's just to add some rigidity to the membrane. It may also help with managing heat in the sense the wider areas will allow for more current, and sink a bit of heat from the narrower areas. I really don't know and have wondered about this myself before.
 
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