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Re:Re:1988 DT50 Electrical

13 Sep 2020 17:36 13 Sep 2020 17:43 by Dave in WI.
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Re:Re:1988 DT50 Electrical #1
I've been slowly bringing an '88 DT50 back to life this summer. It was stored in a shed for 6-8 years so I've had to do the usual- clean it up, de-rust the tank, rebuild the carb, new battery, and I had to get a new petcock. I've got it running pretty good now and I want to get it on the road so I can run around the neighborhood.

The issue I'm up against now is getting the headlight to work. The lights DID work years ago. I am only getting a fraction of a volt at the headlight connector. Switch continuity checks good.

I have a factory service manual pdf I got off Ebay which has been very helpful. It has some good electrical diagnostics which I have been following.

It gives a procedure for checking the charging voltage which is good. at 7.2v. It also give a procedure for checking the charging and lighting coil resistances. The charging coil, which I believe is good because it charges :-) is supposed to have a resistance between .26-.34 ohms. My check is .6-.7 ohms. But as I said, it works.

The lighting coil resistance is supposed to be .20-.24 ohms, I get .5-.7. The manual does not give a procedure for checking the lighting coil voltage output. I checked it by back-probing the connector where the coil resistance is checked, with the bike running, and I get a fraction of a volt.

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I was originally was thinking the regulator/rectifier might be bad. But I get the same fraction of a volt before the regulator that I do at the headlight connector.

Having said that I believe the lighting coil is bad. If anyone has any words of wisdom I'm all ears. The lighting coil is NLA but with some Googling I think I can find one. But before I fire the parts cannon, am I missing something here?

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13 Sep 2020 19:12
MarkT
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Re:Re:1988 DT50 Electrical #2
I'd test the lighting coil output with the wire out of the stator with it not connected to anything... engine running of course.

If regulator is bad and it's connected, the voltage will be low anywhere in the circuit... before OR after the regulator.

It's not like the wire before the regulator will have 9 volts and after the regulator the wire will have 6 volts. It doesn't work that way.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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14 Sep 2020 05:12 14 Sep 2020 05:47 by Dave in WI.
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Re:Re:1988 DT50 Electrical #3
Thanks Mark. I can do that by disconnecting the CDI magneto connector, and running wires between the white and black (so it will supply power to the ignition and run), start it and test for voltage between the yellow/red and black. Sound right?

Edit- if it helps here is the wiring diagram and the test for the charging coil.

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14 Sep 2020 11:15
MarkT
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Re:Re:1988 DT50 Electrical #4
Just unplug the regulator/rectifier (three wire plug at regulator.)

Just don't rev the engine too much. Should have decent voltage at white and yellow/red at regulator plug even at idle.

If not, then unplug the handlebar switch and see if that changes anything...

Finally, with reg and switch unplugged, probe the wires as close to stator as you can.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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14 Sep 2020 11:29
Dave in WI
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Re:Re:1988 DT50 Electrical #5
Thanks I’ll give that a shot.

In related news, I have tested the existing headlight and I know the bulb is blown. It appears to be a sealed-beam type, NLA of course.

I’m about to take a flyer and buy the below off ebay. It doesn’t show dimensions or voltage, but it sure looks like it’s close enough. The connector is not quite right but I can make that work.

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14 Sep 2020 12:02
MarkT
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Re:Re:1988 DT50 Electrical #6
That headlight is probably not a sealed beam. Looks like the "replaceable bulb" type?

Would be great if it fits!!!!

P.S. I have a couple of new original headlights... bought a couple for spares right before they went "NLA". They were like $93 each at a "special price" if I bought them all! List price was well over $100.

They are kind of more like an "assembly" if I remember correctly... comes assembled with rim and adjuster. If you can't make something work, I can spare one. Or try going to your local Yamaha Dealer. They have a "parts locator" where they can check stock at other dealers (even though Yamaha might not stock them) and maybe find you one? Sometimes I've been put in touch with a dealer someplace that has some parts and will sell and ship at a great price... (Unfortunately these headlights weren't one of those deals... but they were the last ones showing up in the US database at the time.)

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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14 Sep 2020 13:56
MarkT
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Re:Re:1988 DT50 Electrical #7
Also, are you using the meter on AC volts? Headlight circuit is AC.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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14 Sep 2020 20:33
Dave in WI
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Re:Re:1988 DT50 Electrical #8
Now THAT’s a good question. I was indeed using the DC setting. I never thought of that. My meter has 200 and 600 volt settings for AC, when I get the chance I’ll test it and see what I’ve got. Wouldn’t it be cool if there’s no problem, just operator error.


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15 Sep 2020 10:01 15 Sep 2020 16:49 by Dave in WI.
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Re:Re:1988 DT50 Electrical #9
So one of the benefits of working from home is, I can pop out to the garage and do stuff on my lunch break.

I put my meter on the 200v AC setting and checked the voltage at the headlight connector.

The readings I got were 3.5v at idle, 4.6v at 5,000 rpm. Lower than specified. I guess that’s why the high beam indicator light works.

So is this good enough? If not where do I go from here?

Edit- next step, I’ll disconnect the regulator/ rectifier and check the output with it running.

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15 Sep 2020 19:25
MarkT
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Re:Re:1988 DT50 Electrical #10
You can wait and see what happens with new light... I'd clean all the connections, especially the contacts in the hi-lo switch.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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