VR setup trouble

[rug]

Board: 3.0
processor: MS-II

I am trying to get my engine started today. I thought I had a good RPM signal, but I didn't, so I found this guide to tune the pots for VR sensor:

Adjusting R52;
With MS 'OFF', Using digital multimeter;
poke -ve test lead at pin1 of U7 and
+ve test lead to pin 3 of U7. Adjust R52 to get 100k. (or the closest possible).

Adjusting R56;
With MS 'ON', VR sensor connected;
Poke -ve lead to 'GND' at proto area and
+ve lead at 'base' (centre lead) of Q23.
Adjust R56 to get 0 (zero) volt. (or closest possible).

When I measure resistance on pin 1 and 3 on U7, I get around 45k as max. I can't get more. What did I do wrong? Or is the pot broken? I also tried measuring the resistance at the pot, and I get 45k there too. It works fine on the jimstim.

/Carl

[Peter Florance]

I am trying to get my engine started today. I thought I had a good RPM signal, but I didn't, so I found this guide to tune the pots for VR sensor:

Adjusting R52;
With MS 'OFF', Using digital multimeter;
poke -ve test lead at pin1 of U7 and
+ve test lead to pin 3 of U7. Adjust R52 to get 100k. (or the closest possible).

Adjusting R56;
With MS 'ON', VR sensor connected;
Poke -ve lead to 'GND' at proto area and
+ve lead at 'base' (centre lead) of Q23.
Adjust R56 to get 0 (zero) volt. (or closest possible).

When I measure resistance on pin 1 and 3 on U7, I get around 45k as max. I can't get more. What did I do wrong? Or is the pot broken? I also tried measuring the resistance at the pot, and I get 45k there too. It works fine on the jimstim.

/Carl

Sometimes I have to rotate R52 and R56 CW a turn or two from max CCW (turn CCW until you hear clicking)

[rug]

Doesn't help. I get a nice linear decline of resistanace from around 45k down to 0.

I am going to go buy a new pot and see if it works better...

/Carl

[Peter Florance]

Doesn't help. I get a nice linear decline of resistanace from around 45k down to 0.

I am going to go buy a new pot and see if it works better...

/Carl

If VR sensor output is too low, 0 volts for R56 will not work. That's the one you want to rotate CW to raise it, maybe by one volt.

Sorry I had forgotten which was which.

[rug]

I will try tuning R56 a bit.

But that still does not explain why I do not have 100k on R52. I even replaced R52 and still get 45k on that one. Off the board, both pots show 100k, so somewhere on the board, I loose 55k ohms?!

/Carl

[Peter Florance]

I will try tuning R56 a bit.

But that still does not explain why I do not have 100k on R52. I even replaced R52 and still get 45k on that one. Off the board, both pots show 100k, so somewhere on the board, I loose 55k ohms?!

/Carl

What is the value of R53?

I jiust check a board (turned R52 until it clicked) and got 105K ohms

[rug]

R53 shows 9,89 kohms on my meter.

Playing with R56 did not help at all. When cranking my engine I sometimes see RPM spikes, but nothing constant at all. Still works fine on the stim.

/Carl

[rug]

The pot has a total of 100k resistans. So, when I had it off the board, I see 100k between the middle pin and the top pin, and 0 on the lower. If I change to 50k, I have 50k on both sides. But when I put this on the board, I see 45-50k on the top one, and 0 on the lower. Hope that makes sense. It doesn't make any sense to me

/Carl

[rug]

I still have the issue of 45k, but I changed switched polarity on my VR sensor and got a much better RPM signal. Either the picture of what was + and - on a ford sensor was wrong, or I was just stupid at the time of wiring it all up

Recharging the battery ones again... will try starting again later this afternoon

/Carl