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1965 BJ8 Tach
- Thread starter John Egan
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RAC68
Darth Vader
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Hi John,
As many have, In the 1990s, I experienced eratic readings on my Smiths tachometer caused by a deteriorating electronic component. If I remember correctly my replacement of the diode did satisfy my issue. However, your description seems to point to a part called a thermistor that adjust the circuit to changes in temperature (see circuit below). The problem with replacing this unit is that I was unable to find the specifications for gaining a replacement so, if it is the cause, hopefully you will be able to gain some information from printing on the unit.
Hopefully this helps,
Ray(64BJ8P1)
As many have, In the 1990s, I experienced eratic readings on my Smiths tachometer caused by a deteriorating electronic component. If I remember correctly my replacement of the diode did satisfy my issue. However, your description seems to point to a part called a thermistor that adjust the circuit to changes in temperature (see circuit below). The problem with replacing this unit is that I was unable to find the specifications for gaining a replacement so, if it is the cause, hopefully you will be able to gain some information from printing on the unit.
Hopefully this helps,
Ray(64BJ8P1)
Bill Young
Senior Member
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John
I have been doing some work to reverse engineer the Smith's RVI tachometer. I have done a couple of rebuilds using new transistors, capacitors and thermistor and have achieved linear indication from 0 to 7000 RPM. The thermistor is not easily identified. Tom Haydon of the Sunbeam Club has done a lot of work to identify this device and we think the 330 ohm 3560k rating is close to the original. I am currently working on a temperature controlled box to see what low and high temperatures do to the calibration. Send me your email address and I will send you a .pdf of the attached .jpg drawing. This is a preliminary drawing as I work through design and bill of materials. I am planning a 3 part article for the Healey Marque magazine starting in January showing repair and calibration.
Bill Young, BJ8, BN2, AN5
sjahc.com
I have been doing some work to reverse engineer the Smith's RVI tachometer. I have done a couple of rebuilds using new transistors, capacitors and thermistor and have achieved linear indication from 0 to 7000 RPM. The thermistor is not easily identified. Tom Haydon of the Sunbeam Club has done a lot of work to identify this device and we think the 330 ohm 3560k rating is close to the original. I am currently working on a temperature controlled box to see what low and high temperatures do to the calibration. Send me your email address and I will send you a .pdf of the attached .jpg drawing. This is a preliminary drawing as I work through design and bill of materials. I am planning a 3 part article for the Healey Marque magazine starting in January showing repair and calibration.
Bill Young, BJ8, BN2, AN5
sjahc.com
