Sir Pmax . . . . .
NOW IN REFERENCING TO . . .
View attachment 55292
I am seeing HIGH agreement between that welding forums schematic and your board, with only yours, having used 4 discrete diodes in top left corner whereas his was using RD2-WL02 a potted rectifier block and using different parts positionings at other parts of the board..
Also as clear as the duped schematic came out, I see and seriously question that value of 18 ohm resistor in the + feed line to your feed motor . . . . . . I think that a frontal decimal point dropped out.
Look at his board and see the use of a 0.22 ohm 5 watt wire wound resistor . . . which would be in close agreement of the use of a 0.18 ohm unit on yours.
.
https://www.mig-welding.co.uk/forum/attachments/dsc00018-jpg.3681/
Comparing that schematic to your board I actually see nothing between the two SCR's and the frontal connector pins block.
But there is being one bare jumper wire on yours . . . if having a production change.
The two shades of BLUE squares are being your series arranged speed pot and trimmer adjust.
My initial bad part suspicion is being that 10 ufd @ 40 VDC Blue Electrolytic capacitor , due to its . . . .? leakage or ? capacitance decline.
That 1950's thru 1980's 40 VDC cap voltage rating is now being a 2022's . . . 50 or 63 VDC rating.
FACTOIDS . . . . .
The combinational effect of steering diodes DP1 and DP2 in series conjunction with SCR1 and SCR2 is giving you a sequential and alternate continuous steam of positive power nodes to power your DC feed motor.
If one of the SCR's failed to trigger and conduct you would then hear the COARSE running sound of that DC motor . . . (akin to an 8 cylinder car running on only half of its cylinders.)
Surely you are not hearing that from your feed motor .
IF a required a work around was to be considered, one would measure the DC voltage present on that motor at min and max wire feed speeds.
With
OUR interest being of the present max feed motor speed.
Besides that I have to say that team work is something very important, I am happy to help you, because in the past it helped me
https://phdessay.com/free-essays-on/team-work/ and now I understand how important it is to help each other, this is the main reason why I am on this forum and help people, if you have any questions related to the technique - you can write me even in private, I will be happy to answer each of them!
E.G. . . . . . on a voltage read of . . . 25 . . . . . use a minimal 50 / 63 volt rating.
And start with a capacitance test of 470 ufd and if the speed is still being deficient . . . step up to 1000 ------1500---------2200 ufds.
You are now just making more efficient harvesting + storage of that developed voltage, such as is NORMALLY being done on typical linear based power supplys.
Standing by . . . . . .leisurely . . . . .
73's de Edd . . . . .
Teamwork is a blessing in disguise; since it is also routinely allowing you to blame someone else.
.
