Welder Dave
Senior Member
Tried it again today and ran perfect. Flipped the switch to high idle and no burping or hesitation at all even even when it only ran for 20 seconds.
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Engine only runs with full choke
- Thread starter Welder Dave
- Start date
I seemed to have to flash the old miller on the service truck I was using back in the day, don't know why it would not hold the magnetism. Either a crusty mess carburetor, or fuel pump/ restriction and its not filling it all the way.
Welder Dave
Senior Member
There could have been crap in rubber fuel line (that came loose) after the inline filter. That would also explain why it would only run on starting fluid until I blew air through the line. Maybe what ever was blocking the fuel got caught in a jet in the carb. It would be nice if it just needs to be flashed but it was welding good. Maybe a little corrosion or dirty slip rings??
LCA078
Senior Member
Glad you got one problem solved. To keep the carb clean, I'd change out the inline filter and replace the hose between the filter and carb. As said above, old fuel lines will release garbage internally...and it doesn't take much to gunk up a jet.
Welder Dave
Senior Member
I did put a new filter and hose on. The hoses that came with the filter were too short to use both of them but the existing inlet hose (before the filter) was in decent condition. I have some new hose at my property and will change the inlet hose when I get a chance. I also want to put a shut off valve on the gas tank. It's kind of dumb someone took the original sediment bowl/fuel shut off off. The welder engine is running good now so the first priority is to get it welding. Then I'll clean up to get it ready to sell.
Tugger2
Senior Member
Im no welder repair guy,but we ran big 40 s on our camp welding trucks a lot. The only welding end failure i saw was the diodes .Especially when they just sudenly quit welding for no reason. They are right on the end and easy to change.
Welder Dave
Senior Member
They are generally pretty reliable. I hope it's something simple like diodes. One of the guys at the repair shop thought the brushes might need to be changed if it was sitting for awhile.
A couple things. I have decades in small engines. You were most certainly not getting enough fuel. One thing that will continue to bite people is WATER! You go buy E10 fuel, but Ethanol is high hygroscopic! Meaning in a tanker with 70% humid air sloshing around, it's sucking up water, and water is heavier than the fuel. This sits at the bottom of the bowl and absolutely IS a lack of fuel, because it's trying to run on water! Fuel sampling is a big part of my madness! Always have a glass mason jar around.
Other is actual blockage in a jet. Do NOT go changing carb settings! If it ran perfect before, it's NOT a setting issue! Always examine passages before the "cleaning" so you know where the issue is. I can't even tell you how many carbs I fixed that were "just cleaned" via DIY.
Yes, you should have a filter without question, just before the carb!
Welder Dave
Senior Member
It could have been a little water in the float bowl but I'm more inclined to think it was some deteriorated rubber or crap in the fuel line. When I first tried to start it it would only run on starting fluid for a few seconds. When I blew air through the fuel line to the carb after the filter it ran properly. At first anyway then it acted up again so I got a new filter. Still would only run on choke but ran good after draining some gas from the float bowl. I think some crap came out but could have been a couple water droplets.
Welder Dave
Senior Member
Repair shop did an inspection and the no weld condition was due to bad diodes. All 6 of them! Updated Miller part number was $400/each!!! Old part number was $135 or $165/ea. I can't remember. I was still in shock at a $2500 repair bill! The guy even said the $400/ea. was ridiculous. They had a used parts machine with good diodes they'd sell for $500 so I went with that. Fan belt was cracking so they'll put on a new one. It was $50! The engine had a front seal leak but Continental is no longer. They don't do aftermarket but said if it's not used all the time to just check the oil. They also said the engine didn't rev. high enough but I told them it did weld good before the diodes blew. Maybe more crap in the float bowl? They'll be able to tell better once it's running with the working diodes. No rhyme or reason for diodes to go bad. Hopefully the used replacements last a long time. About $800 with labour to fix. I won't make much but should make a little profit if I sell it. $1300 into it and will try to get 17-$1800 for it. I want to keep the trailer for my SA200 but would sell it for the right price, $1500 or so. It's a nice compact tandem axle.
Post pics of the diodes. I'm deep in electronics and I find today's repair shops just aren't, they are parts changers. It's common for OEMs to put some stupid, proprietary feature in a part. On a diode pack, that would likely be easy enough to convert to off the shelf parts. Diodes are selected based on values and specs. Generally the new stuff would be far superior.
Diodes don't typically just 'go bad', but they can take certain damage that shortens their life. Most common is over voltage, which smokes them instantly if high enough, then over current. Usually over current can be prevented with system CTs and alarms.
Diodes don't typically just 'go bad', but they can take certain damage that shortens their life. Most common is over voltage, which smokes them instantly if high enough, then over current. Usually over current can be prevented with system CTs and alarms.
If this is right, page 39, top of page is output stage. KMART simple system! 3 phase welding generator with multi tap secondary, which is your variable voltage. You can see all the rectifier diodes as D2-D7. It would be absolutely critical to probably just replace C2-C7 caps and VR1 as well. In a welding application, those caps can help protect the diodes from odd reverse voltage spikes. VR is varistor, that is also there to help as snubber to protect the diodes.
LCA078
Senior Member
I'm with Fastline on this one. Diodes don't just fade, they die quickly because of something...usually heat from over-voltage causing over-current that fries them. I'm willing to bet dollars to donuts, when you lent out the welder, they cranked up the current which overloaded one diode (from a failed snubber or cap) that then cascaded the load on the other diodes....and then poof...there went the electric ghost.
Should be easy to source aftermarket parts for a lot cheaper.
On Page 55 of that manual, it shows two diode parts: 037 957 and 037 956. You need three of each to rectify the 6 halves of the 3-phase set up. I see those for sale on ebay for less then $50 each. Are they genuine? No idea but then again, it's just a diode...
Should be easy to source aftermarket parts for a lot cheaper.
On Page 55 of that manual, it shows two diode parts: 037 957 and 037 956. You need three of each to rectify the 6 halves of the 3-phase set up. I see those for sale on ebay for less then $50 each. Are they genuine? No idea but then again, it's just a diode...
I have my own theories, and much of it comes from coming in AFTER the "techs". If the 6 are ALL actually bad, that is rare, and losing one will not overload the others because as part of a 3 phase system, each diode pack is limited as a function of the generator. Willing to bet the generator is designed to reach full saturation before a diode blows up. Like when you weld your hot stick to the metal. What is maybe more likely is a high voltage event, like welding on something that has power. DC voltage can stack up when a series circuit is created.
Who knows, but what I commonly see is the "replace them all" approach. I'm NOT saying that is bad in this case, but I would sure want my old parts back, even if bad. I always trying to do my best in failure analysis, to prevent future drama.
Other is a total misunderstanding, in which a meter was used with all diodes and caps in circuit, one is bad, but others can 'read' bad in circuit. This is why you do both in circuit and discrete testing. As just an example, I hunt electrolytic capacitors like a bloodhound on gophers in circuit. I'm not looking for a specific value, but I know how the meter should respond.
LCA078
Senior Member
I hear you that one bad diode shouldn't cause the others to fail but in a 3 phase system, when one diode goes bad, the other two on that half-wave side can still source/sink current to make up for the one lost one. The three phases overlap...unlike a single phase. But yes, I agree a good electrical design that has buffer in sizing components should be able to handle a single bad diode with ease.
And yes I wholeheartedly agree, most modern "trouble shooters" can only read the troubleshooting checklist from the manufacturer. True electronic troubleshooting skills are rare these days. It's more of a guessing pluck-n-chuck method. It's definitely frustrating....
And yes I wholeheartedly agree, most modern "trouble shooters" can only read the troubleshooting checklist from the manufacturer. True electronic troubleshooting skills are rare these days. It's more of a guessing pluck-n-chuck method. It's definitely frustrating....
Pluck-n-chuck...... LMAO
But why should I care, I've made some solid buys on equipment with electrical issues. However, tell me it was hit by lightning, but "it's minor", and I'm out! Or that Harold the hack already had a go but ran out of wire nuts.
But why should I care, I've made some solid buys on equipment with electrical issues. However, tell me it was hit by lightning, but "it's minor", and I'm out! Or that Harold the hack already had a go but ran out of wire nuts.
Welder Dave
Senior Member
The guys that borrowed the welder were running low amps welding some trailer axle brackets on overhead. The weldor even ran a bead before they headed out and said it welded really nice. Got everything tacked in place and the welder died part way through the first bead.
The welder is a 1974 (HE prefix) so likely a little different than the one referenced but similar. The shop fixing it specializes in engine drives but can't warranty aftermarket parts. They said they've had issues with aftermarket parts in the past so won't use them. They probably had 30 engine drives in their shop and over 40 in the yard for parts. I'd guess a lot in the yard were too expensive to fix and the owner either didn't want it back or the shop paid a small amount for it for the parts. I've read when one diode goes bad the opposite one usually goes bad too. Apparently moisture, rust, overheating or just old age can kill diodes. The welder sat outside and was hardly used for 25 or 30 years. Hopefully the used diodes will last a long time. The engine runs great so I figured the welder is worth $800 in repairs. $2500+ not so much.
The welder is a 1974 (HE prefix) so likely a little different than the one referenced but similar. The shop fixing it specializes in engine drives but can't warranty aftermarket parts. They said they've had issues with aftermarket parts in the past so won't use them. They probably had 30 engine drives in their shop and over 40 in the yard for parts. I'd guess a lot in the yard were too expensive to fix and the owner either didn't want it back or the shop paid a small amount for it for the parts. I've read when one diode goes bad the opposite one usually goes bad too. Apparently moisture, rust, overheating or just old age can kill diodes. The welder sat outside and was hardly used for 25 or 30 years. Hopefully the used diodes will last a long time. The engine runs great so I figured the welder is worth $800 in repairs. $2500+ not so much.