Tach guts

[Dan Himan]

I removed and opened my wifeys 1988 944S tach to compare, (she was not happy about it). How much for the 87 944S tach? I have $40 in my pocket.

[desertt5]

Spots on the face are oil off my work bench. Will clean off fine.

[bens944]

Originally Posted by porsche4life

Radioshack still sells resistors, if your local store is decent...


What year cluster is that from... I've got a few I'd sell you the tach out of....

Do you still have any tach's 1985.5 944? How much?

[walfreyydo]

Originally Posted by bens944

Do you still have any tach's 1985.5 944? How much?

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=porsche+944+gauge+cluster&_sacat=0

[Monkey Wrench]

I think what you need is a clear picture of another one with no blown parts for ID.



you can just buy a kit with all the sizes and pick what you need. I'd favor the flameproof ones as they aren't that expensive.

caps and resistors have maximum values, thats the voltage they can handle. If you go a tad larger it shouldnt; matter much if the value is correct. smae wiht capacitors, they have a working voltage. if the working voltage is for example , double, it's probably not an issue.

https://www.justradios.com/reskits.html

here's another source:
https://www.digikey.com/en/products



the other blown component might be a capacitor but you'd have to see if you can find any markings or a board photo of a good one for that ID. can you read anything at all on them?

I doubt that you will find a schematic, its likely proprietary.

don't use aluminum foil as you can't solder to that, but there is thin copper foil used by people who do art glass windows , or you can just use small wires as jumpers and jump any breaks.


here is a resistor code calculator if you can't remember them all..
https://www.digikey.ca/en/resources/conversion-calculators/conversion-calculator-resistor-color-code


or you can use this to remember.

"bad boys raped our young girls but violet goes willingly"

no don't just measure that resistor, it will be a meaningless value if it's too burned to read..

I work on old radios so Ill normally lift one leg and measure them but if you want to measure it in circuit. there may be a way that current can bypass the probes via some other route in the circuit, so if you lift one leg that excludes that as a possibility.

however, a secondary path will not ever INCREASE the resistance, it can only reduce resistance, so if the resistance value is too high , you can find that in circuit without unsoldering one lead, in order to take it out of circuit. .

I sometimes work on old tube radios, in general when the resistors fail they go higher in value or open , they don't normally usually decrease in value. ( in other words they don't often become more conductive with age)


near the edge of the board there are two electrolytic capacitors. I can;t see the values in the pic. one is red and one is black. see that stripe on the black can? that is the negative side. You can replace those for reliability but I'd check that you can read the values and polarity here is important so keep track of the way they were and don't put the new ones back "bass ackwards." ;-)

what Id do whit those two caps, is clip them with pliers above the board and then take your new caps and wrap the leads around a needle to make a coil shape on the end, then you can solder to the segment of old lead that you left. if you prefer you can solder to the board. it wont matter from an electrical viewpoint, it just avoids needing to heat the circuitboard.

you can test capacitors but they are cheap so I'd just renew them. they tend to fail with age , resistors and other parts may be fine.

[Monkey Wrench]

looks like the undamaged circuit board has flameproof resistors in place of the regular ones that appear burned in the first set of board pics.

Maybe it means there was a revision or a repair on the second board? If the factory saw those two parts failing, they may have increased the watt value of the resistors to make them more reliable ?

something important here. did you alter any wiring or make any mistakes like hooking up jumper cables backwards or any unusual electrically related event that preceded the failure? short some wire by accident? "stuff" happens ! If there is an electrical problem a quick way to mess up is to replace the board before you correct the issue that caused it to blow.

sometimes boards like that have a label or a revision number. I saw there was a paper label on the microchip, perhaps with a date or rev number? if they change the way the logic works there could be other revisions of the chips. Maybe the label there indicated the rev number of the microchip.

appears they are soldered in, Ive worked on machines where a factory would send out revisions in the form of an eprom which a chip that looks similar, then we'd just have to pop out the old one and replace it and that's how they upgraded the machine to have new functionality. I think those shown are soldered in.

if you find a date code you can compare that to the year of your car and see if it is perhaps any newer.

if you have more money than time then Just replace, if you are short on cash the actual electronics parts are cheap and there is no guarantee, but if you try and fail you probably aren't much further back.. maybe you get lucky.