Lister LT1

[mobile_bob]

send me your pictures
front and back, and try to clean the board up as best you can, use a heat gun on low heat and carefully remove the wax, so we can see the color codes on the resistors and maybe some other components,

keep the heat away from the ic chip, that little rectangular thing with all the spider legs coming out of it, and also there is a round can that i would try to keep the heat off of too.

you might try mineral spirits and an old tooth brush, it may soften the wax and remove it without heating.

heating can be done safely, if you are careful and use some finesse, that usually comes with experience, so if you are not comfortable doing that, try the mineral spirits, if you are from across the pond i think they call it "white spirits" or somesuch, it is available at the paint stores.

while you have a couple of electrolytic capacitors that have either died or dieing, i don't think they are causing the problem you are having.

in the last picture i think i see one of the slip rings over the top of the board in your hand, in the background, it looks to be in need of a good polishing up.  use some fine grit wet/dry paper (around 400grit) and make the rings bright and shiny again. 

i can't tell you how many generators quit or become intermittent due to oxidized slip rings and crud on the brushes,   i always start with cleaning both up, and i think maybe 90% of the time the generator comes back to life again.

Bruce would know, but i don't think a good design would use electrolytic caps in the voltage reference section of a regulator,  used for filtering or smoothing yes, but in a reference circuit?  i don't think so, they generally are so loose on their spec's its hard for me to see a use where they would have any application on controlling reference voltages in a regulator.

so i think the regulator might still be working, it is just probably not working as cleanly as it should.  and there are components on the board that need clean power, or filtered power, which the electrolytic caps would be used for in my opinion.

in any case, start with the simple, clean the slip rings and the commutator if it has one, and the brushes, the brush faces can be cleaned by placing a strip of 400 grit backside to the slip ring and grit facing up toward the brush, and then simply pull the paper out again, the brush spring will put enough pressure on the brush to hold it against the paper, and the paper being laid over the slipring will maintain the contact arc/shape so that the brush will fit nicely on the now clean slip ring.

if that is over explaining? sorry, i don't know your experience level.

whatever is causing he issue, it probably will be easily rectified (fixed).

bob g
i will pm you my email addy, you might also pm Bruce and sent him the pictures too, he has a lot of experience with regulators on these types of applications, i would defer to his knowledge and use me as a fall back position. 

[mobile_bob]

so you have cleaned the slip rings, and the brushes and are making good power, it is just intermittent?

if so then maybe there is a problem with the board, (likely so) and we got to get into it.

pictures are hard to determine tiny faults, but it could be that there is a loose (cold) solder joint,

we need the pictures, and maybe we can determine what the capacitors need to be, get them replaced, and then also reflow the remaining solder joints on the board, at least any that look at all questionable.

the fact that it is intermittent tells me it is a bad connection, and it may well be one or both of those capacitors on the board are intermittently going open (or shorting) and maybe causing the problem. 

i am not as suspect of the ic chip, in my experience they either work, or they are dead, not many that are intermittent?  maybe Bruce can shed some light on that.

lets not get ahead of the horse, lets go set by step.

i don't think you have any major winding problems, although it is possible, i think that is really a small chance of being the issue.

check all connections,

another thing you can do, is put a volt meter on the brushes while it is running, and see if the brushes are being powered up,  i suspect they have to be when the generator is running normally and with a load, but if you see the load power drop off, look at the meter and see if the brushes are also not getting power at the same time.  that would tell us that the regulator is the problem, however if the generator stops putting out 230volts under load, and the brushes are still getting pretty much the same voltage supplied to them as witnessed by the meter, then you have something going on with the windings or connections internally in the generator stator or rotor.

push comes to shove, if it were me, i would seek out a tech to come have a look, a good tech could find the problem in 15 minutes or less, and most of that would be getting out his tools and setting up to test.

it can be really difficult to diagnose via computer communications. sometimes it is something as simple as a crack in a circuit board breaking a trace, causing an intermittent, and that can be really hard to see in a picture on a computer screen unless the board is every clean, picture taken in good light, and from several angles.

bob g

[Welderherup]

Rings are clean. Brushes are clean. Getting 50v from the brushes and now getting 180v across those big capacitors at the bottom of the power head and about 50v from the plug socket but it’s difficult figures every time a start it now. What should it be at the brushes?

[BruceM]

I don't know this LT-1 generator so when you mention and show big capacitors at the bottom that leaves me befuddled without a circuit diagram showing what those  capacitors are for.  Hopefully someone familiar with the LT1 can set us straight. 

[mobile_bob]

Bruce +1 for having no idea what the lt-1 generator is, however it looks very similar to
various ones built back in the 50's-60's and into the 70's

the board places it likely late 70's or newer, i don't think i have seen circuits using DIP package chips on anything older than maybe the late 70's?

the two big caps i have seen, and i believe they connect to each brush, and my thinking is they smooth the field current and in doing so improve the brush life, and maybe cleanup the waveform on the output a tiny bit? they might even improve flicker on some slowspeed applications?

iirc miller welder generators used these sort of capacitors, as did kohler, and i think winco generators, maybe others?

hopefully this issue can be resolved fairly quickly, i don't know about you, but i don't have any hair on my head i am willing to loose trying to sort this puppy out.  i do hope the OP can get it sorted, as it looks to be a nice quality genset and something we never see around these parts.

[BruceM]

Weldherup, 50 V (DC?)  at the brushes should be plenty, but it depends on the rotor coil windings. The readings at the capacitors of 180V (DC?)  is inconsistent with 50V DC at the brushes if the capacitors are doing as Bob suggests.  There's a big difference between AC and DC volts in this situation, so I don't have enough info regarding measurements or schematic to add much more. Any local generator repair technician should be able to get this sorted very quickly if it's over your skill set.

I concur, Bob, on the date of manufacture of the electronics as no earlier than mid 70s.   Easy to reverse engineer and cheap to repair.
 






 

[cobbadog]

Never ask me about electrickery but having just repaired a circuit board on my MIG welder today after 6 weeks of looking at it, finding issues with a diode, a small capacitor and finally the relay switch it is working again. While I was waiting for the relay to come on the slowest boat from China I spent a lot of time at the work bench with a desk lamp and a magnifying glass searching for suspect 'dry soldered' joints and found some joints I was not happy with so a quick touch with the soldering iron and a dab of solder and that was sorted. It was the use of the light and magnifying glass that found the capacitor problem and the diode was an obvious failure.
I used mineral turps to wipe over the board but my board did not have this wax covering. If you were here in Oz at the moment you could leave the board out in the sun and wipe off the wax as it gets the solar treatment but I am guessing you are near snow conditions soon so that is not an option. Acetone might be another option as to dissolving the wax but check with the guys if that would cause any issues.

[BruceM]

Methinks you're being too modest, Cobbadog.  Repairing a modern MIG welder circuit board is a major accomplishment; I can't imagine how much magnifier and precision work that must have been for surface mount PCB rework.  Bravo.
Bruce

[cobbadog]

Thank you for your very kind wordss but there would be no way I could have done it with out the enormous help from members on a welders forum who knew wha to look for and there for they guided me through the repair.
Yes, my electric soldering iron was like using a sledge hammer on a thumb tack but with persistence I got there.
The capacitor measured 2-3mm in length and close to 1mm in width. So small I 'borrowed' Dees tweezers from her sewing machine to place and hold it while I put a tack on one end.
I only had a go at what I was advised to do by people who have the 'smarts like you' on what to look for and do. I am proud that I actully did it but I do not understand what it is I did as electronics seem to avoid my b rain pettern and wont stay and allow me to understand them. As to have the ability to reverse engineer circuitry, now that is a true talent and IO tip my hat to those who can.