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Re: LDR for the SCC

Saw this on one of the other Saab forums, so I made a quick note of it:

Photo cell for trip computer- available from Maplins, part no.:N47AY (range 16k-23k Ohms LDR)

Hope this helps.
 

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Hmm, that doesn't match the impedance I measured which was circa 400kOhm in bright direct light to circa 7MOhm in darkness...

I've tried searching but haven't found anything in that range.
 

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Got me thinkng and I re-visited the old discussion here? .

The impedance I've just quoted is when it's fully enclosed in the SCC case.

Measured without the case around it, under very bright light it gets down to about 8kOhm
 

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Hi I saw that hinted at in the Archives.

Could you use the Dash adjust switch as a variable resistor??
I was thinking of possibly attaching it to the current Dash lights adjuster or putting in another one

Cheers C
 

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Originally posted by Mark E:
[qb]Hmm, that doesn't match the impedance I measured which was circa 400kOhm in bright direct light to circa 7MOhm in darkness...

I've tried searching but haven't found anything in that range. [/qb][/b]
Mark, was that the resistance of a correctly functioning LDR. I stripped my SCC to look for serial numbers yesterday to no avail.

It seems like this is a common fault with the SCC. I checked the analogue clock on my other 9k, and the LDR was physically different. I may just buy a selection for the SCC from RS and play around. I'll let you all know if I get is sorted out....

Simon
 

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Ok, my SCC now works correctly.

I used an LDR N49AY LDR from Maplins it was £0.99 for the LDR and around £2.50 for next day delivery

Its a 10 minute job to remove the SCC and re-solder the LDR in. You can connect it either way round. There are 3 holes in the PCB, so make sure you push the LDR legs through the same 2 holes that are currently used.

The old LDR was open circuit (over 20 MOhms), so the display was maximum dim. It works very well now and reacts even when driving through tunnels.

Hope this helps- it was annoying me for around a year and only cost £3.50 to fix

Simon
 

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simonf,

superb info, I've been trying to source this info for ages. Just one question, what model and year is the car, and do you know if the type of resistors varies from year to year ?
 
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