1981 330 A/BP DC issues

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I've just acquired a 330 A/BP and after getting the years of dust, dirt and grime removed, wiring it up and putting in the shop, I've begun playing with it for SMAW with some 6010, 6011, & 7014.Having played around with electrons once or twice in life, I've found that on AC this is a dream machine. On DC, it's castrated, to say the least. I've studied the schematics and it appears that one of the following is at play:-The power diodes are going bad-The Stabilizer "Z" (large inductor) is burned up-A bad connection somewhere in the DC only connections (switch).In an attempt to alleviate the problem, I've cleaned the contacts in the switch, tugged on every connection and nothing seems amiss. When I pulled the diodes and checked them, I get a 0.4 v drop one direction, and an open the other. If they failed this test it would tell me if they were completely bad, but I'm not sure that they're not starting to fail. When running with an AC clamp meter it appears that the current through one set of Diodes is much higher than the other, but still not as high as I would expect it to be. When running in AC mode I measure the current that I'd expect at the welding lead, so I'm quite sure that only the DC portions of the power circuit are affected.Does anyone have guidance on what to look for in a failing rectifier? I'd like to know that the diodes are bad before I sink any more money into this.
Reply:So it just seems to have low amperage on the DC side? Did you separate all the diodes before testing them? Make sure the input jumpers are correct? Have you checked OCV for the AC and DC side? Which position is the knife switch in? There's not a lot to go bad in these old machines (same as my Airco)Last edited by SquirmyPug; 8 Hours Ago at 07:08 PM.Airco Ac/Dc 300 HeliwelderMillerMatic 200 (stolen)Miller Maxstar 150STLMiller AEAD200LE (welding and generating power

) Hobart MIG
Reply:Thanks for following up. I have the knife switch in the correct position (SMAW, or METALLIC), and the OCV voltage is correct for both AC and DC, but when I strike an arc with DC, the voltage is low, around 15-25 volts, jumping around a lot, while on AC, the voltage is stable around 31-32 volts.As for the Diodes, I did pull them so that I was only measuring the individual component. I've also run the AC clamp meter on each diode, and found that they are not carrying the same amount in current, whether in AC or DC. In AC mode, each diode set is run in parallel, but DC puts once from each set in series.