Jump to content
Indianajohn

A 520H oil light question with a twist!

Recommended Posts

Okay folks, I am dealing with the typical Onan oil pressure light switch issue, but with a bit of a twist. A DPO apparently got tired of seeing the light on and cut the leads and removed the LED! So, I'm wondering if anyone has ever replaced any of these LEDs, and what the correct replacement part would be? Would really prefer not to have the expen$e of replacing the whole light module just for lack of a single LED.

BTW, I believe I have a found a cheap replacement for the high $ Onan oil pressure switch. I won't know for sure that it works properly tho until I can replace the LED. If it does work, I'll do write-up here on it with pics.

  • Like 1

Share this post


Link to post
Share on other sites

LEDs are standardized electronic parts. The ones in the light module are probably common 5mm panel-mount LEDs. I haven't needed to take my panel apart, so I don't know the details of how it goes together. Typically, panel-mount LEDs have a "shoulder" molded on the back side which keeps the LED from poking too far out of the hole it's inserted in. Once in a while, you'll see a plastic or rubber grommet with a groove on both the inside and outside edges used to hold the LED in position in a panel hole, but usually the LED is just soldered to a board which is mounted behind the panel. The LED is inserted into the board to a specific depth on the leads and soldered on, and the excess length of the leads is cut off -- so it's held in place and positioned by how it's soldered in. It's easy to do, especially with the others present as a guide. The only trick is to watch the orientation of the leads -- you have to orient them correctly for + / - in the circuit or the LED won't light up. Look at the other LEDs to tell. One edge of the back of the LED is flat, and the lead that's next to it is the "-" lead. Circuit boards should also be marked for polarity of LEDs, and sometimes have the outline of the base of the LED, including the flat edge, printed on to help you orient it.

 

I'll guess and suggest that the LED to use is probably a 5mm panel-mount, diffused type. "Diffused" means the translucent plastic has a slightly frosted appearance to make the whole LED glow nicely, not just show a tiny pinpoint light. You'll also have a choice of normal or "super-bright" LEDs. The super-bright ones are more visible in daylight, but depending on how the light panel was designed, WH might have used slightly less-expensive standard LEDs. If you want to be sure you can spot the oil pressure light, you could try a super-bright one, although it might be really bright if you look at it in the garage!  Either way, LED's are cheap so try whatever you think is best.

  • Like 2

Share this post


Link to post
Share on other sites
Posted (edited)

Well, the biggest problem is that not all LEDs use the same voltage. That's where I'm running into an issue. I've tried getting a voltage reading off the left over leads still sticking up, but have no success there. These are the clear/white LEDs that light up red, and they are potted into the module, so you can't just unsolder one to take into Radio Shack and match it up. In fact it's going to be a bit tricky replacing this one, because I'll have to carefully solder the new leads onto the stubs of the old leads.

But at least I can report that the hour meter is now working properly, so I know that at least that side of the new switch is working as it should.

IMG_2482.JPG

Edited by Indianajohn

Share this post


Link to post
Share on other sites

Well, most LEDs run between 1.8 and 3 - 3.3 volts, depending on the resistor in the circuit and the current it's supposed to carry. There are other ranges, but that's the common range. Those, a little surprisingly, look like super-bright LEDs (They're more commonly packaged in clear housings) -- which means Wheel Horse was OK with higher-priced components. Most manufacturers will try to shave fractions of pennies, since it adds up in production!

 

Unfortunately, the previous owner didn't do you any favors by cutting the old LED out of a potted board. The potted board is a good thing since it will hold up better on a tractor, but it makes component-level repairs next to impossible with all that thick epoxy.

 

If you can clip a digital voltmeter's leads onto the exposed LED pins left in the panel, you might be able to catch the voltage being applied when you turn the ignition on and the light test runs. That will give you the voltage to the LED after the dropping resistor; from there you can estimate an appropriate voltage tolerance for the LED -- it should be somewhat higher than the reading you get on the meter. LEDs are cheap and might be worth experimenting with to see if you can repair it.

Share this post


Link to post
Share on other sites

We'll, I did try a clear/red LED touching it across the leads ( observing the same polarity as the other LEDs in that row), and it did not light when I turned the key on. I was using a 3 volt 35ma LED. I then tried connecting my Fluke DMM across the leads and trying again. Not a flicker of voltage. I'm starting to wonder if they didn't somehow damage something on the board when they removed the old LED. I'm assuming there has to be some sort of driver circuit for these things. Of course, with everything potted in the way it is, that pretty much makes repairing anything on the board an impossibility. May end up having to replace the whole unit after all......

Share this post


Link to post
Share on other sites

Is this the newer style without the test switch ?

 

If so I have one you can have for the cost of postage.

 

Cleat (in Canada so postage will be a bit more).

 

  • Like 1

Share this post


Link to post
Share on other sites

Thank you! Yes, it is the newer type (no test switch). I would very much appreciate it! Really want to know if this new o.p. switch is working properly, then I will do a write-up here on how I did it. Hopefully this will save someone else a lot of money over the stock Onan switch. I will PM you with my info.

Share this post


Link to post
Share on other sites

Any updates on this oil pressure switch, IndianaJohn? I'm struggling with this myself right now...

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Recently Browsing   0 members

    No registered users viewing this page.

×