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Onan 6.5NHD Spec M - The resurrection.


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  #141  
Old 07-05-2012, 11:46:26 PM
len k len k is offline
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Default Re: Onan 6.5NHD Spec M - The resurrection.


LK
I would NOT try to remove silver disks (~3/8 inch diameter)on the carb, I don't think there is anything under them.

Magnetite
This was a while ago, but one of the disks covers the idle mixture. I drilled it out and removed the needle. It needed cleaning and adjusting.


1) Where was the silver disk you drilled out and found a needle under.??
In the attached picture was it at arrow 1 or 2 ?? ( I also found needles in the dip tube inside the carb bowl.

2) What did you replace the drilled out disk with , and what did you use to seal it?
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  #142  
Old 07-06-2012, 04:21:32 PM
Magnetite Magnetite is offline
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Default Re: Onan 6.5NHD Spec M - The resurrection.

Quote:
Originally Posted by len k View Post

LK
I would NOT try to remove silver disks (~3/8 inch diameter)on the carb, I don't think there is anything under them.

Magnetite
This was a while ago, but one of the disks covers the idle mixture. I drilled it out and removed the needle. It needed cleaning and adjusting.


1) Where was the silver disk you drilled out and found a needle under.??
In the attached picture was it at arrow 1 or 2 ?? ( I also found needles in the dip tube inside the carb bowl.

2) What did you replace the drilled out disk with , and what did you use to seal it?
It was arrow number 1. If you look at Fig. 20 of the NHD Service Manual 965-0500 you'll see the prior version of this carb - before they covered over the idle mixture needle with a cap. You can see that they just put in a smaller head for the needle and a collar over that head to allow the seal.

The seal isn't necessary for anything other than keeping you from adjusting the mixture. I admit I wasn't sure if the needle might vibrate, so I put back the same cap, with a hole in it where I drilled it. It's not air tight. It doesn't need to be. I just pressed the cap back in place. It's easy enough to hook it back out.
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  #143  
Old 10-27-2012, 02:22:58 PM
len k len k is offline
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Default Re: Onan 6.5NHD Spec M - The resurrection.

Well.... huricane has upped my repair priority for my voltage regulator a bit. I have a 7NHMFA26105H with a voltage regulator 305-0826.
Got the potted board out of the aluminum case, got lucky ..... it's clear potting.
The bottom traces of main circuit board looks identical to Magnetite's board (middle pic of post #53. My board also says Onan ...on 1-st line , also says 332-3508.A on 2nd line (likely raw board number), but says LAC-2 2000-(then a square box) on 3-rd line.
Just as it says in Flight Systems pointman manual , it looks like they use the same circuit design in many Onan gensets.

Magnetite.....you said in future you may cleanup the circuit schematics you posted, if you did, it would be very helpfull. Also do you think the IGT can be tested in circuit without damaging rest of regulator, looks like you said 100K in series with gate of IGT

Got the datasheet on the IGT you replaced it with, got to learn how to test the old IGT.

To test IGT, I'm thinking maybe 9 or 15 vdc across IGT CE leads ,with light bulb in series , then a pullup resistor to either + or -. (I have the datasheet)
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  #144  
Old 11-07-2012, 10:32:49 AM
Magnetite Magnetite is offline
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Default Re: Onan 6.5NHD Spec M - The resurrection.

Quote:
Originally Posted by len k View Post
To test IGT, I'm thinking maybe 9 or 15 vdc across IGT CE leads ,with light bulb in series , then a pullup resistor to either + or -. (I have the datasheet)
I answered your email on this, but late. I've been offline for long periods. Let us know how you did, as I'm interested.
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  #145  
Old 11-09-2012, 01:45:18 AM
len k len k is offline
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Default Re: Onan 6.5NHD Spec M - The resurrection.

Really nothing much to report. Started working on it just before huricane, I assumed igbt was shorted, makes sense. Figured out leadtimes were going to be an issue, learning about igbt, shipping, rework, gen shealter, powerleads to house. Huricane turned away from me, priority dropped.

I have to give some thought on how to test an IGBT, would like to test it incircuit before I de-pot more. Concerned about damaging ceramic daugther board circuits with electrical igbt tests. Did you test it incircuit, if yes, how. What do you recomend? Is my idea on above post (bat+bulb) OK?

I tried some tests just now with ohmmeter, I'll PM the results to you. Don't want to clutter up thread with technical garbage that may not be right. Want to do some tests on igbt first , want to minimized ammount of de-potting.
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  #146  
Old 11-09-2012, 10:36:34 AM
Magnetite Magnetite is offline
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Default Re: Onan 6.5NHD Spec M - The resurrection.

I had two problems on mine. One was multiple bad solder connections between the ceramic daughter boards (the outer board was the main problem) and the other was the blown IGBT.

Initially I just pulled the IGBT and tested it. It was bad. I then ran the VR on the bench. I found the info in this thread on the Basler regulator to help:
http://www.smokstak.com/forum/showthread.php?t=80209

I realized that the IGBT gate wasn't seeing the PWM signal from the outer ceramic daughter board, and looking closely, I then realized that several solder connections were broken between the two boards. I tried (unsuccessfully) to resolder using conventional Pb-Sn solder. Eventually, I went to specialty solder used when I do surface mount rework.

At that point I retested the VR with a pot hooked across the voltage adjust leads, 120VAC hooked to the monitor leads and watched the gate signal on the scope. As I cranked up voltage adjust, I would eventually cross the threshold where the VR would be trying to boost output above 120VAC. Of course, since it was sitting on my bench and the VR was monitoring the "fake" 120VAC derived from line (I actually used a variac so I could adjust it), the increased duty cycle of the PWM signal wouldn't actually do anything.

I expected the gate PWM signal to jump from 0%-100% DC quickly as I crossed the threshold by turning the adjust pot, but instead it would slowly increase to 100% even without any additional rotation of the pot. The time delay was about 1/2-1 second to go from 0-100% - presumably to prevent oscillation and add stability.

I hope that helps.
IIRC, I never actually drove a load with the IGBT when testing. I had a new one and I'd tested out of circuit that the old one was bad and I'd tested
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  #147  
Old 02-13-2014, 03:47:19 PM
len k len k is offline
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Default Re: Onan 6.5NHD Spec M - The resurrection.

Was thinking about the IGBT. For thermal reasons likely would be better if replacement did not have an internal free wheeling diode, (assuming same Vce). This diode free wheels every time the IGBT shuts off (~120 times /sec). A seperate one would lower the watt disapation in the IGBT package allowing it to run a little cooler, as Onan designed it. Ignoring duty cycle, ~3amps times .7 volatge drop is ~2 watts of heating.

My experience with these To-220 packages is it's 100 watt rating is VERY UNreasonabe in typical usage, would require a POWERFULL active liquid cooling system to keep IGBT temperature within specs at 100W. It's heat sink is pretty pathetic.

Last edited by len k; 02-13-2014 at 04:20:17 PM. Reason: typo
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  #148  
Old 07-12-2015, 03:56:57 PM
len k len k is offline
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Default Re: Onan 6.5NHD Spec M - The resurrection.

Thought others repairing this AC voltage reg may like to know an easy way to get potted board out of the aluminum box. Easier to unpot and reuse the box. My AC voltage reg is # 305-0826 but it's same design as Magnetite's , my gen is 7NHM spec H

I carefully drilled a hole in back of aluminum box using a tile cutting carbide tip (end mill type bit) so it wouldn't grab and drill thru board. Board is held about 3/16 inch off bottom of box. I put head of a nail down the hole and pushed potting off of box, so air pressure could act over a larger area, more force. Then pushed a tire valve stem against hole to make a air seal, applied 150 psi air and it popped right out, like a piston. Between a little oxidization of aluminum, and/or mold release that I think they used, the potting doesn't stick to the box.

http://www.smokstak.com/forum/attach...6&d=1387862252


So far I've used a razor blade to cut and peel back potting on solder side of board only in area of IGBT leads to test it, I think it's shorted. I don't intend to unpot whole board, I suspect that is what broke Magnetite's ceramic daughter board connections to main board.

Will be a bit of trouble to unpot the IGBT and resistor assembly board. It's not designed for easy unpotting. On junk computer boards for easy mass unsoldering of many joints at once I just scan hot exhaust of a propane torch across the joints( at a large distance so they melt but don't burn. Got lucky my potting is clear, so I can see what I'm doing.
.

Last edited by len k; 07-13-2015 at 02:25:49 PM.
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  #149  
Old 02-28-2016, 02:52:26 PM
len k len k is offline
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Default Re: Onan 6.5NHD Spec M - The resurrection.

Took the IGBT out of my reg yesterday. It's number is SGP30N60. Googling that number shows it's specs are 600 V , 30 amp Vce = 2.5 . I'll start a separate thread on my rebuild later, just wanted to post that # here so others can compare it's specs to Magnatite's IGBT.

That reg goes on my 7NHM, and is very likely the same board as they used on Magnatite's NHD reg.
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  #150  
Old 02-28-2016, 03:08:27 PM
KPack KPack is offline
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Default Re: Onan 6.5NHD Spec M - The resurrection.

I wonder how Magnatite is he was pretty sharp.
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