1 reply to this topic

[mreibman]

So a friend of mine recently got a Koford M700 controller. That's the electronic one with a full choke. (you can see a pic here: https://www.koford.c...ontrollers.html) These controllers run $589 MSRP.

 

So when he got it in a box of stuff we found it did not work.

 

I saw him Saturday and he gave the the controller to work on if I could find what was wrong.

 

Well, Sunday morning I start looking at it, and poking to see if anything is obvious like a broken wire or something. Nothing was apparent, but the board with the meter kept getting in the way. I marked and cut the two wires to the meter just so it wouldn't be annoying.

 

The meter (Marked slot car meter on the back) does not work, even when hooked up directly to a power supply. (clue #1) It's two-wire, so even I can hook that up correctly. :-)

The controller suddenly worked.

 

I retested by using some clips, but putting the meter back on made the controller not work.

 

I put in one of the meters I typically use which is a three-wire, but it did not cause the controller to not work.

 

Some cosmetic work and cable management and I was in business.

 

Question(s):

- What on earth could cause a meter to keep a controller from working? 

- Obviously the meter is bad, is it something Koford might replace (or even sell the part?)

- Should I just say "ok, all set"?

- Does anyone have any kind of diagrams for the Koford electronic controllers? Mostly what wire goes where, and what components are end user replaceable?

 

[Bill Seitz]

I looked up the Koford description, and this is a PWM controller using MOSFETs. I don't see it in your photo, but there's going to be at least 1 IC generating the pulse drive which could be a digital microcontroller, and a bad meter might have caused a short making it not work. As you have your meter connected across V+ and ground, I can't see how the meter could stop the controller from working, but there's not enough of the circuit wiring to give a more definitive answer. Koford hasn't made this controller in a while and doesn't sell a replacement voltmeter. You'd need to contact them to see if they can repair this controller.

 

What's interesting to me is that the photo appears to be the 2 MOSFETs, and these are TO-247 devices that are now obsolete. The currently available MOSFETs are in smaller package/case sizes and would been some finagling to fit in the TO-247 pad spacing. Guessing from what I can tell from the configuration in the photo, the FET on the left is the electronic choke, and the one on the right is the actual output transistor.

 

I have the electronics background that I can usually figure out how to repair or sub parts on most analog controllers. Where a digital microcontroller is used, replacing one of those usually requires programming the part which I don't have the facilities or expertise to do. You'd probably be able to replace the MOSFETs and passive devices without too much difficulty, though as I mentioned with the transistors, there might not be drop-in parts that would require some extra work to make fit.