75 280Z Clock Repair?

[HusseinHolland]

20 hours ago, zclocks said:

OOPS! that didn't come out right. The 2M ohm resistor provides bias for transistor so it is almost turning on. The higher the resistor value the lower the voltage(bias) and the transistor might not turn on . The first coil detects the magnets on the flywheel as it passes and generates a small electrical pulse in the first winding. This pulse passes through the 10uF cap going to the base of the transistor and turns it on. Current then flows through the 2nd winding through the 680 ohm resistor. This current produces a small magnetic pulse which gives the magnets a "push" when they pass through the coil and keeps the flywheel turning.

If you can push the flywheel to start the motion and the flywheel continues to move then the transistor is working . However, it 's just barely working.

That being said I'm not sure that the transistor is turning on hard enough to get the ball rolling , so to speak. 

 

Thanks again for the functional description - it's nice to understand the sequence of events taking place on the board 🙂

I have some M- range resistors coming. If playing with that doesn't produce positive results, I think I'd just as soon buy a refurbished board from you. 

[Dave WM]

hmm did you happen to test those caps before replacing, specifically the .22? that looks like its function is to kick off the process.

fyi, I ALWAYS check parts before installing them. I have found while rare, new parts can be bad and lead you down rabbit holes. Try tacking on a known good (assuming the replacement is open) cap there and see if that will get it going. 

[HusseinHolland]

11 hours ago, Dave WM said:

hmm did you happen to test those caps before replacing, specifically the .22? that looks like its function is to kick off the process.

fyi, I ALWAYS check parts before installing them. I have found while rare, new parts can be bad and lead you down rabbit holes. Try tacking on a known good (assuming the replacement is open) cap there and see if that will get it going. 

I didn't test the new caps, I wouldn't have a clue how to even do that. I could swap them out for other new caps, but what I have is all from the same batch I bought off Amazon.

[zclocks]

You need a capacitance meter to check caps. 

 

 

 

[SteveJ]

10 hours ago, HusseinHolland said:

I didn't test the new caps, I wouldn't have a clue how to even do that. I could swap them out for other new caps, but what I have is all from the same batch I bought off Amazon.

As @zclocks said, you need a meter that can read capacitance. I prefer to use my Fluke for that. However, if you don't want to spend $200 for a Fluke, you can always try a cheaper alternative like this: https://www.amazon.com/AstroAI-Multimeter-Ohmmeter-Voltmeter-Non-Contact/dp/B0842HTN8C

It's just as easy as putting the meter on the capacitance setting and touching the leads to the two wires on the capacitor. By the way, having a capacitance meter can be handy for testing your home AC. I've used it to find a dead run capacitor for both of my units and a friend's unit. Having a good meter saved me a few hundred in service calls.

Edited September 13, 2023 by SteveJ
Fixed callout to Ron

[HusseinHolland]

1 hour ago, SteveJ said:

As @dutchzcarguy said, you need a meter that can read capacitance. I prefer to use my Fluke for that. However, if you don't want to spend $200 for a Fluke, you can always try a cheaper alternative like this: https://www.amazon.com/AstroAI-Multimeter-Ohmmeter-Voltmeter-Non-Contact/dp/B0842HTN8C

It's just as easy as putting the meter on the capacitance setting and touching the leads to the two wires on the capacitor. By the way, having a capacitance meter can be handy for testing your home AC. I've used it to find a dead run capacitor for both of my units and a friend's unit. Having a good meter saved me a few hundred in service calls.

 

7 hours ago, zclocks said:

You need a capacitance meter to check caps. 

Yeah, My OTC multimeters are from the 80's. I guess it may be time to invest in newer tech. 😄 

[Dave WM]

Trouble is sometimes stuff you buy is counterfeit junk, not saying this is the case for you, but its why I tend to get my electronics from mouser and stick with namebrand stuff like Nichecon, also on caps I look for high temp ratings since I do a lot of vacuum tube stuff. Its a long shot that the new cap is bad, but not unheard of.

[HusseinHolland]

51 minutes ago, Dave WM said:

Trouble is sometimes stuff you buy is counterfeit junk, not saying this is the case for you, but its why I tend to get my electronics from mouser and stick with namebrand stuff like Nichecon, also on caps I look for high temp ratings since I do a lot of vacuum tube stuff. Its a long shot that the new cap is bad, but not unheard of.

I did look on Mouser, doesn't look like .22uf is available except surface mount. In any event, I've ordered a new OT multimeter that has the CAP feature. Should be here Friday, so I'll test the components I have.

[zclocks]

I bought one of the capacitance meters on Amazon for $22 . I  compared it with my old B&K 820 and it's very accurate. For $22 I thought it was junk , but wanted to see how good it was. Don't think I would check large power caps with it, but a vary nice unit. I check all caps before use for the simple reason I have been burnt several times. Installed what I thought was a new good cap only to find that the part was WAY out of spec.  

 

[dutchzcarguy]

17 hours ago, HusseinHolland said:

  19 hours ago, SteveJ said:

As @dutchzcarguy said, you need a meter that can read capacitance. I prefer to use my Fluke for that. However, if you don't want to spend $200 for a Fluke, you can always try a cheaper alternative like this: https://www.amazon.com/AstroAI-Multimeter-Ohmmeter-Voltmeter-Non-Contact/dp/B0842HTN8C

???

Zclocks said that haha..

I only thought it!  Yes it's handy to have a capacitance meter..  And i realy like Fluke meters!  I got myself a Beckman many years ago, you can throw it against the deck and then in a bucket of water and measure your threefase system while in water.. haha.. never tried that!  (with it's own correct leads ofcourse..)

These days there are a lot of good measuring tools.. get yourself a quality product!  I still got my fully working analog meter of 1978!!   ANALOG! I still use it from time to time.. i sometimes use it measure capacitance with the ohms-meter.. (Can't tell the capacitance but i can see if the capacitor is dead ..)

[dutchzcarguy]

My 45 year old analog multimeter..

[Dave WM]

Since we are talking cap testers, my cap tester is very old school, uses a  bridge circuit and a vacuum tubes (inluding the eye tester). good for checking leakage on high volt stuff. I also have a multimeter that I use for testing low voltage stuff..

The main point of the video was not to just test caps, but to show how to use this tester to make sure you dont make orders of magnitude errors when replacing caps, especially considering how values are represented differently throughout the years.

 

Edited September 14, 2023 by Dave WM