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65 CLASSIC 770 INSTRUMENT CIRCUIT BOARD

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Alfa Tech. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Alfa Tech. Quote  Post ReplyReply Direct Link To This Post Topic: 65 CLASSIC 770 INSTRUMENT CIRCUIT BOARD
    Posted: May/14/2022 at 3:59pm
Does anyone know what the function and/or purpose of the devices the bridges the ignition power supply from pine number 6 of the instrument cluster to power input pin on circuit board    of the voltage regulator? 
Its located below the voltage regulator and appears to be a simple copper winding. Mine is working (resistance measured across the two connection spades) and looks like a flat coil on cardboard backing with plastic overlay in the center?
Just trying to understand the technical function?
Forum does not allow me to attach the pictures, can email it you you like.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote george w Quote  Post ReplyReply Direct Link To This Post Posted: May/14/2022 at 4:42pm
Probably the noise suppression choke on radio equipped cars. If it is, it’s there to suppress electrical “clicks” coming through the radio speaker that’s caused by the IVR switching the 12 volt power on and off rapidly to effectively feed the fuel and temp gauges at a 5 volt level.
Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: May/14/2022 at 4:53pm
Originally posted by Alfa Tech. Alfa Tech. wrote:

Mine is working (resistance measured across the two connection spades)
It shouldn't be more than a few ohms. As long as the temperature and fuel gauges are working, this choke is good. You can short it out and the gauges will still work, but there may be noise heard in the radio as george w said.
69 Javelin SST BBO 390 T10
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Alfa Tech. Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2022 at 11:52am
Thank you for your collective responses.
Actually the gauges are not working and that is the reason I took out the instrument cluster.  I will remessure the resistance again, if I recall correctly last quick check was around 150 ohm

I have replaced the voltage regulator, cleaned the contacts on all of the pins, checked continuity of all connections and everything is good, however the gauges do not work as well as instrument light.  only lights that do work are oil pressure , parking brake and indicators.  I do have 13.5 volt coming to pin # 6 when ignition switch is on. the car is equipped with factory AM radio which works but not being used.

Regards,

Victor
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Alfa Tech. Quote  Post ReplyReply Direct Link To This Post Posted: May/20/2022 at 6:53pm
updating root cause of the problem for general information:

checked every component and printed circuit board imprinted copper line and everything except the gauges are working as they should. The resistance across the noise suppression device was only 0.9 ohms and voltage out of new regulator measure at gauge positive connection is steady 5 volts.  Installed old regulator and voltage is 12.7 volts at same measuring point, I reasoned that the high voltage from time the old regulator was active may have damaged the gauges.  Removed the gauges and dismantle them  , internals of Both are fried and the very fine wire internal winding is burnt out black and wires are broken.

I have to replace both of them as there is no easy way to repair them given the nature of their very primitive construction (may have been the norm in 1965 for a US car).  
I can say from personal experience that European gauges, VDO for example are much better made devices and operation at 12 Volts negating the need for a voltage regulator.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: May/21/2022 at 10:29am
You will never see a steady state voltage on the output of a working IVR. It opens and closes at a slow rate so the output is either 12V or 0V. The average output voltage is around 5V, but that is just a mathematical number. which cannot be measured with a hand-held voltmeter due to the slow switching speed.

If you have done the 7805 regulator conversion, then you will see a steady 5V. The RT Engineering units use electronic switching rather than the OE mechanical switching. You will not see a steady state on those either.

If your old regulator was stuck closed as your test suggests, it may have burned out the gauges. If you put an ohmmeter across the gauge, you should read a few ohms. Open circuit is bad.

If the gauges are similar to the later Javelin/AMX gauges, they use the mounting posts as the electrical connection as well. I found the connection can oxidize over time and that simply backing off the nuts, then re-tightening them can break the oxidization and restore the connection.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Alfa Tech. Quote  Post ReplyReply Direct Link To This Post Posted: May/21/2022 at 11:37am
Thank you for the comprehensive response, the regulator was stuck closed resulting in burned gauges.

the replacement regulator I have installed looks identical to the old one and not sure about its internals, it does however putout steady 5 volts

I have found a 65 fuel gauge and 64 water gauge on ebay, hope installing them will take care of the issues.

do you know what the resistance across the fuel sending unit may be, like to test that one as well.
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