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Re: derkom's attempt

Posted: Wed Dec 04, 2019 4:08 am
by kodak80
Well done on getting this output. Need to check my soldering work.

Re: derkom's attempt

Posted: Wed Dec 04, 2019 8:09 am
by exxos
derkom wrote:
Wed Dec 04, 2019 12:11 am
Oh, I also noticed the shifter is getting rather warm.
Something shorting it out then somewhere :)

Re: derkom's attempt

Posted: Wed Dec 04, 2019 12:48 pm
by derkom
Today I went around all of the SMT IC pins looking for shorts, and I found a mostly-short (~1.5 Ω) between MUX_G0 and BS (43 and 44) on the DAC. Got that removed, but those two pins are still curiously low relative to the R and B analogues. MUX_G0 > BS is now 55 kΩ, where R and B are 1.2 MΩ and 3.76 MΩ, respectively. Seems to have made no difference in my output. I swapped in another shifter, just to be sure that's not causing the problem (after all, it was running a little hot), but no, no change there either. I do notice that today the shifter is running much cooler (very very slightly warm to the touch), so maybe clearing out the near-short has helped there.

As requested, here's the output of the ROM test. Looks good.

rom.jpeg
rom.jpeg (30.99 KiB) Viewed 1082 times

I can't see the output from the RAM or timer tests because the diag software is changing the background colour in a way that's causing a full white screen for me with things the way they are currently (not) working. Given that the "fail" screen is displayable (see ROM test right above), I suspect this means they're passing.

I am tempted at this point to pull the DAC off and stick it back on by hand. I am not really comfortable with the state of the hot air solders, because I fear there might be some paths under the chip that I can't see.

Re: derkom's attempt

Posted: Wed Dec 04, 2019 12:52 pm
by exxos
Would it work if you jumper to mono output ?

Re: derkom's attempt

Posted: Wed Dec 04, 2019 12:54 pm
by derkom
exxos wrote:
Wed Dec 04, 2019 12:52 pm
Would it work if you jumper to mono output ?
Tried that. I don't seem to be able to get any text at all that way. I still get flickering, but nothing behind it.

Re: derkom's attempt

Posted: Wed Dec 04, 2019 12:59 pm
by exxos
You not got a bent pin on the 244 or 373 buffers or something silly like that ?

Re: derkom's attempt

Posted: Wed Dec 04, 2019 1:07 pm
by derkom
exxos wrote:
Wed Dec 04, 2019 12:59 pm
You not got a bent pin on the 244 or 373 buffers or something silly like that ?
That sure would be nice, wouldn't it? :? Nope, they're all good. However, since I have spares, I might as well swap them out just to be sure they're all functioning. Easier than redoing the DAC.

EDIT: Might as well re-reflow the buffer sockets and shifter socket while I'm at it. I imagine it's safe to assume that all the D lines are clean, since the system isn't crashing. But can't prove the same about the DRD lines.

Re: derkom's attempt

Posted: Wed Dec 04, 2019 1:10 pm
by exxos
derkom wrote:
Wed Dec 04, 2019 1:07 pm
That sure would be nice, wouldn't it? :? Nope, they're all good. However, since I have spares, I might as well swap them out just to be sure they're all functioning. Easier than redoing the DAC.
Oh well :). Think you need to check all the inputs to the shifter. You seem to half get good data then corruption.which appears more like a data input issue,

Re: derkom's attempt

Posted: Sat Dec 07, 2019 10:38 am
by Icky
How is the H4 coming along @derkom

Re: derkom's attempt

Posted: Sat Dec 07, 2019 10:50 am
by derkom
Icky wrote:
Sat Dec 07, 2019 10:38 am
How is the H4 coming along @derkom
The silence is deafening, right? :)

I resoldered all of the buffer chips and associated data lines, with no change.

Since I don't trust any of my video-related SMT ICs, I've ordered a bunch more of the selector/multiplexer chips and should have them early next week. It's a local supplier, but also it's a holiday weekend. When I get those, I'm going to replace the ones on the board, and solder the new ones by hand. I don't think the hot air attempts worked out so well on these.

If that doesn't help, I'll swap the video DAC for one pulled from a broken Falcon board I have (board has a crack, but the DAC is fine).

I suspect one of those two operations will fix things up, but if they don't, then at least I'll be confident that those parts are not the problem.

In the meantime, I have some time to get my office back to reasonable condition. :lol: