91 Marathon rehab questions

[joej85a]

Still at it guys. Guess im talking myself through it! So i was reading this thread:
http://www.buggiesgonewild.com/elect...ontroller.html
and i did all the tests. The B+/B- test passed, the M-/B+ test passed, the pot 0-6k test passed, but the B- to M- test did not act as it was described:

B- to M- gave me 24 volts when the solenoid first clicked, then went to 0 as the pedal was pressed. So while the other tests are showing 36+ volts, B- to M- only gave me 24. Any ideas as to the Controller? I want to test the motor to rule it out, and the f/r switch looks like it has been messed with, could that cause the 24 volt reading instead of the 36 or is the controller shot?

Thanks guys, almost there. I just dont want to invest a ton of money in batteries to find out the controller or motor are bad.

[JohnnieB]

You've gotten the solenoid clicking now. Great news.

Neither the diode across the solenoid's small terminals nor the resistor across the big ones is needed to troubleshoot cart. You want to install them after you get the cart running because they reduce arcing on some contacts and make them last longer, but it's okay to run without them for a little while.

The fact you have a voltage between M- and B- and it drops to about zero when the pedal is pushed are good signs, but only being 24V when solenoid first clicks isn't.
It should be full battery pack voltage the moment the solenoid clicks and then smoothly decrease to nearly zero as the pedal is slowly pushed to floor.

Could be the battery pack is wired wrong, or a bad cable/contact in the high current circuit, or bad contact in F/R switch, or motor issues.

Here is a schematic with High Current circuit traced. Just attach your DVM negative test lead as shown in the battery layout drawing I posted earlier and start at M- terminal with Positive test lead, the go back to C terminal on F/R, then to B terminal, Then to S1 on motor, then to S2 on motor and so on until you find full battery pack voltage. The problem will be between the test point where full voltage was found and the preceding one.

The high current path looks like a plate of spaghetti on the schematic, but it is simply a series circuit with an single wire from B+ at the battery pack back to b- at the battery pack with a few limps in between. Here is a drawing that lays it out more clearly.

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Battery pack is sick if it only charges to 36.8V, but it was only on charge for 3 hours.
Put on charge until charger shuts itself off, or at least 12 hours if it is a manual charger.

Let rest for at least a couple hours, then measure pack voltage and individual battery voltages.
Pack voltage = ??.?
If any of the battery voltages are 0.5V or more lower than the rest, they are most likely bad.

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36.8V should turn wheels, especially if they are off ground, but a battery or batteries might be failing completely under load and the motor might not spin if that is happening.

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Hang in there, the cart probably has several problems and they may have to be identified and fixed one at a time.

[joej85a]

JohnnieB, Thanks for the explanation. I ran out to the garage, put the negative probe on the negative lead on the batter it shows in the drawing and began to test the points.
M- = 18+ volts
C = 18+
A = 18+
B = .3 volts (it was a small number)
D = .3 volts
S1 = .3
S2 = .3

I didnt find 36 volts anywhere?

[JohnnieB]

Looks like you've got two problems.
1. Bad connection between C and B on F/R switch. Might be able to just clean contacts and adjust, but considering age, the whole F/R assembly probable needs to be replaced.

2. Low voltage. For this, I would start at main positive terminal on the battery pack and work towards the F/R switch.
That should be 36 to 38 volts or so. If not the battery pack is miswired, or there are some dead batteries.
If battery voltage is in normal range, chack at battery side main terminal of solenoid.
Then the controller side main terminal (when solenoid first clicks from this point on)
Then continue on step at a time to motor and on to the F/R, which I'm pretty sure has problems.

It is also strange that you are getting 18V, or 1/2 the battery voltage, in two different spots with no (very little) voltage in between. Like I said before, the high current circuit is a single current path, which means you should have all or nothing when the solenoid first clicks.

Technically, MS-3 ought to close the NC contacts, activating solenoid, before the throttle pot tells the controller to pass current from its B- terminal to its M- terminal. So, with the MOSFETs not conducting, full battery pack voltage ought to be measured at all test points from M- all the way back to the main positive battery terminal.



There is something going on here that I don't understand yet.

[joej85a]

JohnnieB, thanks for your help here, i will go back and retrace over everythign. I think your point about the FR switch is well placed. I looked at it further and it looks like it has been completely dismantled at one point, and if it was by the same guy that wired it, that could be the problem. There was a forum member here that had a verified working FR switch, controller box, and solenoid for my model, so i went ahead and picked them up. Great price too. I will keep you posted as i chase down these ghosts in the machine.

PS great possibility the 2 or more batteries are shot. I am going to take them all up to autozone and let them do a load test on them.

[joej85a]

SUCCESS! the cart is running, a big thanks for JohnnieB. I found that the FR switch was only engaging bridging one set of wires at a time instead of two. Cleaned and reassembled and bam! i rode it down the street!! Guess i didnt need those extra parts anyway.
Thanks, now that i know it runs, its time to start cleaning her up.

[Bmw2074]

are you interested in possibly selling your extra control box? im haveing a lot of problems with my 91 marathon, and i think it could be the control box.???

[woodrow256]

I would make sure its ur controller before u buy a new one.

[Bmw2074]

I have been trying to get help diagnosing my cart to make sure that my control box is the problem, but have not gotta definite answer on it yet. From what I have read on this site, all my test seem to point to a bad control box though.