75 280Z Clock Repair?

[dutchzcarguy]

7 hours ago, HusseinHolland said:

since it clearly won't jump start itself. Not sure where that leaves me.

My 240z clock does not run but when i adjust it and i set it some to the left and right a few times it will start and run for some time! It stops after i stop the engine or inabout 15 minutes or so.. you can try this.. just wiggle the knob in the middle of the clock.. mine starts if i do that..

[Captain Obvious]

10 hours ago, HusseinHolland said:

 I'm going to assume I helped it. Not sure where that leaves me.

Well I think that leaves you in a not-too-bad spot. If it started all by itself sitting loose with a 9V, but then would NOT start all assembled off the car battery, then that would be more of a problem and mystery. If it never starts by itself but will run indefinitely if given a push, that's easier to deal with.

My quick hit "from my armchair" would be to try a slightly lower value resistor in place of the 2 Meg. Maybe try 1.8 Meg instead. Just to test things, you could parallel another high value resistor (like a 2M or 1.8M) across the existing 2Meg resistor. Just clip it across to see if it will start by itself then. If that works, then you could desolder the 2M and replace it.

[HusseinHolland]

6 hours ago, Captain Obvious said:

Well I think that leaves you in a not-too-bad spot. If it started all by itself sitting loose with a 9V, but then would NOT start all assembled off the car battery, then that would be more of a problem and mystery. If it never starts by itself but will run indefinitely if given a push, that's easier to deal with.

My quick hit "from my armchair" would be to try a slightly lower value resistor in place of the 2 Meg. Maybe try 1.8 Meg instead. Just to test things, you could parallel another high value resistor (like a 2M or 1.8M) across the existing 2Meg resistor. Just clip it across to see if it will start by itself then. If that works, then you could desolder the 2M and replace it.

Thank you for the suggestion - easy enough to parallel another resistor & drop the resistance on that leg of the board. I'll give that a whirl!

[zclocks]

Hussein, 

 After you replace the transistor did the clock start on it's own when power was applied? How long did you let it run before you assembled back in the housing?

My thought is that if it was running and then stopped when you reassembled the wiring (ground and power wires) might have touched the mechanism and caused a problem.

You could have a lot of resistance in the spring and or the pivots of the balance wheel.

Check the spring shape, teeth condition of the pink wheel, and the pivots. If the bearing are worn to excess the wheel will not run smoothly. If you push the wheel it should take several seconds for it to stop. 

Please post another picture of the circuit board mounted in the assembly.

Ron

 

 

 

[zclocks]

Another question . Did you use a second 3904 transistor or is that the original one?

[HusseinHolland]

2 hours ago, zclocks said:

Hussein, 

 After you replace the transistor did the clock start on it's own when power was applied? How long did you let it run before you assembled back in the housing?

My thought is that if it was running and then stopped when you reassembled the wiring (ground and power wires) might have touched the mechanism and caused a problem.

You could have a lot of resistance in the spring and or the pivots of the balance wheel.

Check the spring shape, teeth condition of the pink wheel, and the pivots. If the bearing are worn to excess the wheel will not run smoothly. If you push the wheel it should take several seconds for it to stop. 

Please post another picture of the circuit board mounted in the assembly.

Ron

 

2 hours ago, zclocks said:

Another question . Did you use a second 3904 transistor or is that the original one?

Hello Ron

Thank you for chiming in

I think I had to jump start it when I did the transistor. The wheel moved when power was applied (which it did not after just the cap replacements), but it did not cycle/swing of its own accord. I ran it for a few days out of the housing.

I checked that the shaft/spindle was able to move freely without binding or excessive end play - I had thought perhaps the shaft might have been restrained by the end adjuster, because I had to recenter the shaft when I first took it apart & didn't pay attention to keeping my fingers away from the shaft.

When I assembled it in the housing I was very careful to gradually feed/pull the two wires out through the casing as I placed the clock in the housing.

There is no signs of wear or degradation to the spring, balance wheel, gears or shaft / shaft tips or pivot caps. If I spin the wheel manually, it cycles for a few seconds.

I will take another pic of the clock with the circuit board in place. I was careful to center the coils in-between the wheels.

I did not re-use the mis-wired transistor

Edited September 10, 2023 by HusseinHolland

[zclocks]

Have you used  your car battery to power your clock. I really don't like using the 9 volt battery as they degrade very quickly. You might power the clock from a car battery and see if thing change.

Everything looks good. It acts as if the transistor is not working correctly. When power is applied the transistor is turned on quickly activating the coil which pushes the wheel and everything starts moving.

It might be that a cap that was replaced is not the correct value. It might say 10uF , but in reality it could be wrong. I have a cap meter and measure everything I replace because of the poor quality caps on the market. As the Captain suggested you might check the value of the 2Meg resistor.

I did some checking on the coil values you have, 490 and 153 ohms, and that is right in line with several circuit boards I have so I don't think that 's the problem.

 Ron

[HusseinHolland]

43 minutes ago, zclocks said:

Have you used  your car battery to power your clock. I really don't like using the 9 volt battery as they degrade very quickly. You might power the clock from a car battery and see if thing change.

Everything looks good. It acts as if the transistor is not working correctly. When power is applied the transistor is turned on quickly activating the coil which pushes the wheel and everything starts moving.

It might be that a cap that was replaced is not the correct value. It might say 10uF , but in reality it could be wrong. I have a cap meter and measure everything I replace because of the poor quality caps on the market. As the Captain suggested you might check the value of the 2Meg resistor.

I did some checking on the coil values you have, 490 and 153 ohms, and that is right in line with several circuit boards I have so I don't think that 's the problem.

 Ron

I did connect the clock directly to the car battery (inside the case), made no difference. The caps, I bought one of those sets that has a large range of values.  I replaced all three - 2 x 10uf, 1 x .22uf. I presume all I can do play with the high value resistor, since I can't check the actual values of the caps. 

 

Edited September 11, 2023 by HusseinHolland
typo

[zclocks]

I just measured several ckt boards I have and all are above 2M ohm  by 30% !

[HusseinHolland]

21 minutes ago, zclocks said:

I just measured several ckt boards I have and all are above 2M ohm  by 30% !

Doesn't that mean the voltage drop would be even greater? I assumed reducing the value of the resistor would be the goal, to increase the stimulus of the transistor on the coil?

[zclocks]

Your correct it would be reducing the voltage there by making the transistor turn on harder. The C828 could have different characteristics compared to the replacement values we use today. It could be that the transistor you used needs a slightly higher Base voltage to turn on. 

I think there was more than one  problem here and something isn't right between the 10uF cap on the base of the transistor. Replacing the caps and the transistor usually corrects the problem 90% of the time. If the coil values were off that could be the problem, but they look good. 

If changing the 2Meg resistor with a slightly lower value doesn't work send the board to me. I have a 280 test mechanism that I know works and that can be eliminated.  I have seen problems with the mechanism that don't work like they should and suspect the magnets on the fly wheels have degraded. I can also check the component values and see if they are correct.

 Ron

 

 

 

 

[zclocks]

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.