Newbie
Joined: 26/03/2024
Location: United StatesPosts: 29
| Posted: 03:05am 12 May 2024 |
Much good news to report for today. After unsoldering a few things and testing all my runs with an ohm meter I proceeded with the "poida fix" provided in the link. Bingo.. solved most of my issues. "rusty" told me about this 2 weeks ago but I didn`t have a spare board at the time. Wish I would have done it then, I could have saved myself a few bucks. I am now able to reach my target input voltage of 175-180vdc. Trim pot is to the gnd. side and I have 28vac with a 40watt bulb as a load. Pin15 is at 4.5vdc. Bulb is glowing orange. Slowly, I turn the pot and increase my AC to about 60-65 vac. Bulb is bright, waveform is stable. Nothing getting warm. Pin15 is now at 2.8vdc. Turn the pot more to about 70vac and pin15 is down to just under 2vdc. Go just a little more and pin15 drops to 1.5-1.8vdc and the board shuts down. Haven`t blown a single fet (IRF740) all day. I am certain the remaining issue is in the control circuit now. R19 is at 100K. For R21 I began with a 56K with some control. I tried 68K and it was worse with very little control. I have a 50k in there now. Should I try a 47 or 43K next ? I did quite a bit of testing, although nothing to drastic. Ramp the voltage up and down, applied the load on and off at various voltages. No issues. Max amps never exceeded 1 amp. I would expect thing to heat up a bit as I add more power and load when I get the IRFP460 mosfets. Very encouraging day. Almost there !