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Rectifier Question

  • Brzn
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Rectifier Question was created by Brzn

 '72 DT2, brand new battery put in while doing the refresh this past winter and charging system's working fine.
I just noticed I've blown my second rear tail light bulb in 600 miles. The first bulb was 50 years old, so not a big deal. The second however, was in for only one month before it went out. The rectifier converts AC to DC so would only be in use for those items that require the key to be in the second position, correct? Headlight and gauge lights in the second position. Those items that operate in the first key position; horn, turn signals, brake light and tail light operate off the battery only, correct?
So I may have gotten a bad bulb or vibration made it go out, the rectifier has nothing to do with it. Someone tell me I've got this right please.
Last edit: 05 Jul 2022 06:54 by Brzn.
05 Jul 2022 06:50 #1

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Replied by alnarv on topic Rectifier Question

Put a meter on it and check voltage. (especially at higher revs) Also can verify if AC is rectified. If normal, vibration would be the ikely cause.
05 Jul 2022 07:36 #2

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Replied by Andy L on topic Rectifier Question

Brzn, whilst I'm not familiar with the specifics of a DT2 with regards to key positions, but assuming it follows typical Yamaha wiring notation then off is 0 and then the position 1 is no lights running, position 2 is lights running. Okay, by re-reading your stated logic that the rectifier is relevant in  key position 2 well the rectifier is relevant and needs to operate in position 1 aswell.  This is because it needs to be charging the battery in position 1 so the battery doesn't draindown from the use of all those DC loads you listed correctly in your overall logic process. Hope this helps. Andy
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05 Jul 2022 08:16 #3

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Replied by Gr8uncleal on topic Rectifier Question

Was it the same filament both times? 

Might be worth checking that there isn't an intermittent short in the bulb holder.
05 Jul 2022 08:39 #4

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Replied by MarkT on topic Rectifier Question

Wording of question is a little confusing for me. (What else is new? 

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Rectifier is there to provide rudimentary DC output charge the battery and prevent the battery from draining through the stator coils.

In 1972 a US market model brake and tail light both would run off the battery as required by law here...  earlier US models (change happened around 1970) and other countries had the taillight run off the engine. 

My guess is vibration killed the bulb?
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
05 Jul 2022 09:31 #5

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Replied by Andy L on topic Rectifier Question

Bzrn, I maybe stating the obvious here but are you using the correct replacement rear bulb? It should be a 6V 5.3Watt taillight and 17Watt brake light.   The reason I ask this is because your DT2 model wiring diagram doesn't show a voltage regulator.  Yamaha will have therefore carefully 'balanced' the electrical loads during design and hence why it is so important to fit the correct rear bulb. Andy.
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06 Jul 2022 01:21 #6

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Replied by Brzn on topic Rectifier Question

MartT, you're correct, the taillight operates in the second key position, not the first as I'd stated above. However it operates off the battery, with the motor off. Sorry for the confusion to my question. I'm trying to figure if my rectifier may be faulty and causing the taillight bulb to burn out.

alnarv, Meter on the battery positive terminal shows 6.1 volts with the key in the off position. 5.87 volts with the key in the second position with the taillight on and the engine off. At idle with the key in the first position 6.05 volts and at high rpm's 6.74 volts. At idle with the key in the second position and high beam on (which is where it's at when I'm riding) 6.01 volts at high rpm's 6.95 volts. I'm asking because I don't want to blow the unobtanium headlamp if all I need is a new rectifier.

AndyL, With the bike running and the key in the first or second position the battery should be the voltage regulator, I believe. The 1970 DT2 doesn't have a voltage regulator. It appears the battery is charging fine, my issue is if the rectifier is operating correctly and not blowing out my taillight. I replaced the original 1154 bulb with another of the same picked up at a local auto parts store; Sylvania Longlife 1154 6.4/7V, 6.8/5.3W

Gr8uncleal, Yes, the same filament, the brake light filament was fine on both bulbs. only the taillight one blew. I don't suspect an intermittent short. The inside of the taillight housing looks like new, the socket's in great shape, the rubber around the bulb's socket is in good condition and I'd replaced the wire pigtail between the bikes main harness and the taillight last winter with one I bought from DEET.
06 Jul 2022 10:58 #7

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Replied by alnarv on topic Rectifier Question

The numbers you reported look perfect. I'm with MarkT, likely vibration.
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06 Jul 2022 11:05 #8

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Replied by Gr8uncleal on topic Rectifier Question

As an aside from your current issue (no pun intended! 

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), I strongly recommend fitting a 6v regulator.

I have attached a link to the official Yamaha bulletin on this topic and there are lots of threads on the forum regarding this.

Vintage Yamaha Enduro Fans - Service Bulletin #M5-084 re Voltage Regulators (yamaha-enduros.com)
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06 Jul 2022 11:41 #9

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Replied by Brzn on topic Rectifier Question

Got one!
 
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10 Jul 2022 07:24 #10

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