92 740 speedo sender question...

The speedometer had stopped working, although the odometer was still
running. Replaced the instrument cluster with a used one. The
speedometer then worked for the first test drive, but on the next,
the speedo needle started becoming erratic, and then died altogether.
THis time, the odometer is not working, either. I spliced test
pigtails into the pos. and negative signal wires from the
sender---right at the speedo connector. At 60 mph (more or less)
with a digital multimeter reading rms AC volts, the signal is 2.0
volts. Not much of a signal...but there may be an amplifier. I am
sure it is a pulse train, and so the indicated voltage is probably not
accurate. I don't have a scope to read the p-p voltage, to see if it
is still normal. I would like to know for sure that the signal
amplitude is still high enough to drive the speedometer OK before
telling the vendor that the speedo died the same day installed. It is
maybe not likely, but I could have had some problem with the sender
circuit (and still do) combined with a failed speedometer MPH
needle. (Boy...the hits just keep a'comin!)

I'd just as soon forget the OEM speedo altogether and install an
aftermarket one.....but they don't seem to be common and are
expensive. I found one speedo repair shop that will repair Volvo
speedos, but its very expensive. But then "pot luck" with a much
cheaper used instrument cluster sure isn't working out.

Regards, geronimo

 

What happens if you put your old one back in?

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

A lot of work to swap back to that one...but an idea!

 

The sender is a variable reluctance pickup, it consists of a coil of
wire with a magnet and it senses pips on the differential assembly.
Works exactly like the pickup on an electric guitar, the output is a low
voltage AC sine wave of varying frequency and amplitude depending on speed.

I've never seen an aftermarket speedo for a Volvo but I'd imagine it
would look like an ugly hack. Good used speedometers are plentiful and
cheap, and any TV repair shop should be able to fix the solder joints on
one to get it going.

 

I've seen cars fitted with a $5 bikecomputer glued to the fascia.
Provided you can read it at night, it served to get the car pass the
vehicle check

--

 

Here they don't care whether your speedo works or not....but I care
about not getting tickets. Does a bike speedo really work? Goes up to
75 or so? Seems like the max would be much lower. And how would sender
work? It matters not at all how rigged up the car is, as its next
stop will be the junkyard, I expect.

 

But you can't beat the cost of the job!

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)