Hi again

I found a manual with the impedance vs temp graph in it. The temp senders
did not match this profile (despite being oem replacements). However, the
wire that connects the lot (to my understanding) is supposed to be putting
out 5 volts.

This wire fluctuates between 0-10 volts. Is this normal or have I found why
I have been getting spurious temp readings during long drives? If so, my
plan was to find the start of the wire, put a new wire in and connect
straight to the sender as there are so many potential places the wire has
become compromised.

Cheers

Hammo

In article <C15D1432.EDF6%hbaj2006@aapt.net.au>
hbaj2006@aapt.net.au "Hammo" writes:

> [...] However, the wire that connects the lot (to my
> understanding) is supposed to be putting out 5 volts.
>
> This wire fluctuates between 0-10 volts. [...]

I have not seen the circuit, so this wild-ass guess may be 100%
wrong. But it smells like a 5-volt stabiliser chip is not doing
its job. Either it has blown (and AFAIK semiconductors usually
fail short-circuit, meaning the unregulated input is being sent
straight through to what should be the 5v regulated output) or
the ground connection has become open-circuit (which could be
caused by (eg) a mechanical break or corrosion).

The physical form of stabilisers depends on the power handled:
either what looks like a low power transistor (three wire leads
going into a plastic blob) or a medium-power transistor (three
robust wires going into a flattened package, whose other edge has
a metal tab screwed onto metalwork, commonly with some insulation
between the tab and metalwork).
--
Andrew Stephenson

"Hammo" <hbaj2006@aapt.net.au> wrote in message
news:C15D1432.EDF6%hbaj2006@aapt.net.au...
> Hi again
>
> I found a manual with the impedance vs temp graph in it. The temp senders
> did not match this profile (despite being oem replacements). However, the
> wire that connects the lot (to my understanding) is supposed to be putting
> out 5 volts.
>
> This wire fluctuates between 0-10 volts. Is this normal or have I found
> why
> I have been getting spurious temp readings during long drives? If so, my
> plan was to find the start of the wire, put a new wire in and connect
> straight to the sender as there are so many potential places the wire has
> become compromised.
>
> Cheers
>
> Hammo
>

The voltage at the connector for the temp sender should not be fluctuating.
If the voltage going to the temp sender is fluctuating and the impedance of
the temp sender changes with temp, then the gauge will be inaccurate.

There are 2 possible causes for the voltage fluctuation, and Andrew
Stephenson's is probably the most likely, with a damage wire between the
back of the instrument cluster and the sender being second most likely.

The repair manual has specifications for checking impedance at the back of
the gauge, and I'd bet that the impedance is incorrect. If it is within
specs, then you can run a new wire between the gauge and the sender.
--

Ray O
(correct punctuation to reply)

On 19/10/06 12:42 PM, in article 1161225750snz@deltrak.demon.co.uk, "Andrew
Stephenson" <ames@deltrak.demon.co.uk> wrote:

> In article <C15D1432.EDF6%hbaj2006@aapt.net.au>
> hbaj2006@aapt.net.au "Hammo" writes:
>
>> [...] However, the wire that connects the lot (to my
>> understanding) is supposed to be putting out 5 volts.
>>
>> This wire fluctuates between 0-10 volts. [...]
>
> I have not seen the circuit, so this wild-ass guess may be 100%
> wrong. But it smells like a 5-volt stabiliser chip is not doing
> its job. Either it has blown (and AFAIK semiconductors usually
> fail short-circuit, meaning the unregulated input is being sent
> straight through to what should be the 5v regulated output) or
> the ground connection has become open-circuit (which could be
> caused by (eg) a mechanical break or corrosion).
>
> The physical form of stabilisers depends on the power handled:
> either what looks like a low power transistor (three wire leads
> going into a plastic blob) or a medium-power transistor (three
> robust wires going into a flattened package, whose other edge has
> a metal tab screwed onto metalwork, commonly with some insulation
> between the tab and metalwork).

Thanks for the help/suggestion.

Cheers

H

On 19/10/06 2:55 PM, in article
d3a75$4537063b$180ffe52$15888@msgid.meganewsserver s.com, "Ray O"
<rokigawaATtristarassociatesDOTcom> wrote:

>
> "Hammo" <hbaj2006@aapt.net.au> wrote in message
> news:C15D1432.EDF6%hbaj2006@aapt.net.au...
>> Hi again
>>
>> I found a manual with the impedance vs temp graph in it. The temp senders
>> did not match this profile (despite being oem replacements). However, the
>> wire that connects the lot (to my understanding) is supposed to be putting
>> out 5 volts.
>>
>> This wire fluctuates between 0-10 volts. Is this normal or have I found
>> why
>> I have been getting spurious temp readings during long drives? If so, my
>> plan was to find the start of the wire, put a new wire in and connect
>> straight to the sender as there are so many potential places the wire has
>> become compromised.
>>
>> Cheers
>>
>> Hammo
>>
>
> The voltage at the connector for the temp sender should not be fluctuating.
> If the voltage going to the temp sender is fluctuating and the impedance of
> the temp sender changes with temp, then the gauge will be inaccurate.
>
> There are 2 possible causes for the voltage fluctuation, and Andrew
> Stephenson's is probably the most likely, with a damage wire between the
> back of the instrument cluster and the sender being second most likely.
>
> The repair manual has specifications for checking impedance at the back of
> the gauge, and I'd bet that the impedance is incorrect. If it is within
> specs, then you can run a new wire between the gauge and the sender.

Yep, that'll be the plan!

Many thanks

H

"Hammo" <hbaj2006@aapt.net.au> wrote in message
news:C15E8F5A.2AF6%hbaj2006@aapt.net.au...
>
>
>
> On 19/10/06 2:55 PM, in article
> d3a75$4537063b$180ffe52$15888@msgid.meganewsserver s.com, "Ray O"
> <rokigawaATtristarassociatesDOTcom> wrote:
>
>>
>> "Hammo" <hbaj2006@aapt.net.au> wrote in message
>> news:C15D1432.EDF6%hbaj2006@aapt.net.au...
>>> Hi again
>>>
>>> I found a manual with the impedance vs temp graph in it. The temp
>>> senders
>>> did not match this profile (despite being oem replacements). However,
>>> the
>>> wire that connects the lot (to my understanding) is supposed to be
>>> putting
>>> out 5 volts.
>>>
>>> This wire fluctuates between 0-10 volts. Is this normal or have I found
>>> why
>>> I have been getting spurious temp readings during long drives? If so,
>>> my
>>> plan was to find the start of the wire, put a new wire in and connect
>>> straight to the sender as there are so many potential places the wire
>>> has
>>> become compromised.
>>>
>>> Cheers
>>>
>>> Hammo
>>>
>>
>> The voltage at the connector for the temp sender should not be
>> fluctuating.
>> If the voltage going to the temp sender is fluctuating and the impedance
>> of
>> the temp sender changes with temp, then the gauge will be inaccurate.
>>
>> There are 2 possible causes for the voltage fluctuation, and Andrew
>> Stephenson's is probably the most likely, with a damage wire between the
>> back of the instrument cluster and the sender being second most likely.
>>
>> The repair manual has specifications for checking impedance at the back
>> of
>> the gauge, and I'd bet that the impedance is incorrect. If it is within
>> specs, then you can run a new wire between the gauge and the sender.
>
> Yep, that'll be the plan!
>
> Many thanks
>
> H
>

You're welcome! Let us know what you find.

--

Ray O
(correct punctuation to reply)