I have attached a pic of my tach that is not working. (sat for 37 years). I have read all the posts re: troubleshooting and have followed all instructions. Resistors all read within specs. All soldered terminals check ok. The blue capacitor, (at left of pic) apparently, is often the culprit. It’s the first time I have checked a capacitor, but my DVM has the capability to do so, but I get no uf reading at all. If I try straight resistance, I get no resistance at all and it shows complete continuity.
I was unable to get a close enough shot, but I can only make out “64V” and a “2.5”, but I can not make out any uf value markings?
I do not know what the round (grey/black marked) component is to the right of the transistor?
Does anyone know/recognize the blue capacitor and know what I would want to order to replace it. I am good at soldering, so if that is the problem, I can easily fix the tach if I know what to buy. If that is not the problem, then I will send it to someone!
The two input white wires and the green wire all have the proper voltages and the circuits are wired correctly. It is very clean, internally, and the needle is free without any corrosion, etc.
I’m assuming this is the same type as is on my '68…it’s an inductive pickup from the white wire that is coiled up? If this is the case then have you checked that you actually have power coming to the white wire “coil” from the ignition source? The tach uses that to detect the ignition pulses and so provide a reading on the tach. The aforementioned is my understanding of how these later tachs work, but I aint no engineer!
Yes, I have checked that the voltages are all good. The green wire is 12V with key on and the white wires do carry 12 v from the fuse box to the dizzy. When the tach connector is undone, no start condition due to the white wire to dizzy no longer hot.
Mark,
its very common for that Capacitor to fail. Offhand I cant recall the value, but I think I replaced it with a 2.2uf electrolytic. I dont recall the voltage off hand, but I dont think it was much over 12 volts. A lot of people use a Tantalum cap. either way, its a repair you can do.
I am sure someone will pop in with a proper value.
That must be the 2.5 that I see. I just don’t see a uf after it?? I think the 64V is see just means a MAX load it can take. I will do some searching for the capacitor!
