'91 740 Speedo Problem...Again

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Old 11-15-2016, 10:48 PM
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Default '91 740 Speedo Problem...Again

I just followed the repair tips

https://www.volvoclub.org.uk/faq/Ele...eterRepair.htm

on replacing classic, leaking capacitors on my speedometer and it seems to work well now, except for 1 nagging problem. When I first turn the ignition on the needle jumps to 50 mph, then when the car starts it drops to zero. It will do this for the first 3 or 4 starts then it doesn't do it anymore and works the way it's suppose to. I don't know but it seems to be "charging" something - maybe the capacitors? Is there a resistor that's burned out that should mute that initial signal? Any electricians out there that might know what's happening? Thanks
 
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Old 11-16-2016, 02:54 AM
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I replaced all the caps on my 92 740, using high quality tantalums bought from digi-key.com (electronics component vendor), and it didn't fix mine... the speed won't read above about 45mph 90% of the time, although once in a blue moon it works normally.

My understanding is there's a speedo chip that fails. You can apparently buy this chip from China (the originals were made by ITT), but I never bothered, and just relied on GPS speed when on the freeway.
 
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Old 11-16-2016, 10:07 AM
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Originally Posted by pierce
I replaced all the caps on my 92 740, using high quality tantalums bought from digi-key.com (electronics component vendor), and it didn't fix mine... the speed won't read above about 45mph 90% of the time, although once in a blue moon it works normally.

My understanding is there's a speedo chip that fails. You can apparently buy this chip from China (the originals were made by ITT), but I never bothered, and just relied on GPS speed when on the freeway.
Hey Pierce, are the chips the 2 black, rectangular objects in this pic?
 
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Old 11-16-2016, 10:21 AM
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oh wait.... never mind, the Yazaki speedo on the 91/92 740/940's uses different chips, not the UAF2115 that was used on many VDO speedos :-/
 
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Old 11-17-2016, 10:40 AM
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You know either way, resoldering those chips looks like an incredibly tough job. I think I'll wait for Pick n Pull to get some inventory. Thanks.
 
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