- USB charger from car battery inside house when power goes out - 2 Updates
- Old plasma screen Y_SUS anomalies - 1 Update
| "Peter W." <peterwieck33@gmail.com>: Oct 06 01:21PM -0700 > Peter, I've noticed that Jeff Angus hasn't posted lately. Any idea why? Alive and well, still in Ranger, TX. Peter Wieck Melrose Park, PA |
| Michael Terrell <terrell.michael.a@gmail.com>: Oct 06 11:06PM -0700 On Wednesday, October 6, 2021 at 4:21:31 PM UTC-4, Peter W. wrote: > > Peter, I've noticed that Jeff Angus hasn't posted lately. Any idea why? > Alive and well, still in Ranger, TX. Thanks, I was getting a bit concerned about him. He stopped replying to me when Hillary lost the election, so it wasn't worth the time for me to try to contact him. |
| legg <legg@nospam.magma.ca>: Oct 06 02:32PM -0400 On Wed, 6 Oct 2021 09:41:11 -0700 (PDT), "ohg...@gmail.com" >If you remove the IPM from the board and turn it over, you'll probably find the bottom is open but potted in clear snot. Careful visual inspection will reveal one or more blown open gates. Because I couldn't find a reliable source of IPMs, I started "repairing" them in a way. I used to isolate the bad mosfets from the IPM's ceramic circuit board and mount external ones to the underside of the heatsink, then wire them into the board. Here's a pic of the diagram I drew: https://i.imgur.com/TmQbULi.jpg >I used mosfets and they worked fine, but they did run hot so I always added a fan directly on the heatsink. Even when brand new, these ran stupidly hot anyway so even when I was able to source new boards or IPMs, I always added a fan to both sustain boards to prevent call backs. >The sustain boards are double sided, so removing the IPMs is a bit of a problem. I always preheated the boards and added liquid flux before attempting to suck the solder out of the holes. If you refer to the assumed switch configuration you'll see that the IPM has no connection to the only negative supply rail - its output is actually prevented from going negative by D14. If you refer to the output waveform, you'll see the IPM doing its think in the waveform's preliminary hash, where it switches quickly between Vs and gound. There are no other switches that can do this, except for those in the IPM. There were no blown fuses on this board, and the IPM shows highZ/bodyVf diode readings on the pins for SUS_OUT, VS and GND, when lifted. I had no trouble desoldering the IPM using a normal iron, one pin at a time, for removal. It has a solid black epoxy body - part number SPI-42X39090-2. The Y_SUS PCB is 3-layer. One of the 3 paralleled external fets had avalanched and gone resistive between gate and drain to overload -VY. With this was fixed, the buffer board seemed to pump -VY more negative than its regulated -200V, increasing to -250V or more to put the parallel fets into danger of avalanche). A new buffer board prevented this. The external heatsunk mosfets DO get hot. The two parts ID'd as 900V operate in their linear mode to develop the ramps, using a miller-cap/diode network between gate and drain. These two slopes are visible on the sick puppy's panel drive waveforms. I suppose that if the SUS_UP slope was slower and continuous, then a ~ book waveform could be created, using the end of drive period as the SUS-DN, per older 'return to -VY' methods. The book timing (40us/div) suggests that SUS-UP and SUS_DN are expected to complete in ~ (+)100us (-)80us time periods. Sick puppy's SUS_UP (50us/div) is too quick. The components in the 900V part's set-up miller network seem to be OK individually. Maybe if it was slower, the waveform might magically turn into a single pulse, rather than a double one. . . . . ? RL Still don't know why the buffer test point doesnt follow SUS_OUT. I'm working with a dark screen - a few pin-pricks of colour visible in a dark room. RL |
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