Troubleshooting #22
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(Apologies if this is was already apparent) did you press reset? |
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Happy to say I did try the reset button. When the reset button is pressed the screen gets slightly brighter and on some resets a diagonal run of pixels will shift. In roughly a fifth of power on events a very regular pattern of straight lines will display. The same snow type screen as pictured above is seen if the system is powered on with the ssd flash removed which leads me to think the problem is related to address or data paths running to and from the ssd. |
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The static-image you're seeing pre-reset appears on a working system, so
that isn't an indication of a problem. The snow is just an accurate
representation of "there's junk in the video memory before reset".
That you're seeing that *probably* means the VGA-related stuff is good (you
have valid sync, etc), so the problem is probably on the computer-logic-end
of the board.
If you connect via UART, do you get anything?
…On Sun, Jun 30, 2024 at 9:17 PM TwoPigsToTheWind ***@***.***> wrote:
Happy to say I did try the reset button. When the reset button is pressed
the screen gets slightly brighter and on some resets a diagonal run of
pixels will shift. In roughly a fifth of power on events a very regular
pattern of straight lines will display.
The same snow type screen as pictured above is seen if the system is
powered on with the ssd flash removed which leads me to think the problem
is related to address or data paths running to and from the ssd.
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some core things to double-check:
- are all the chips in the correct alignment; there are a number of flipped
chips
- there are 74HC02 chips and the 74HC4002 chip on the board, and those are
different: are you sure you have those differentiated?
- what's the voltage between GND and 5V? (should be close to 5.0)
- how much power is the board drawing? mine is ~1.0 W
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voltage looks good, drawing .15amps so right at 1w power, that does decrease to .11 when the reset is pressed before recovering. chip placement has been checked by two sets of eyes. thinking at this point it is either a bad chip or a bad solder joint. |
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Can you connect via UART? (500_000 baud, 2 stop bits, it should say
"READY." after reset coming out)
…On Mon, Jul 1, 2024 at 3:40 PM TwoPigsToTheWind ***@***.***> wrote:
voltage looks good, drawing .15amps so right at 1w power, that does
decrease to .11 when the reset is pressed before recovering. chip placement
has been checked by two sets of eyes. thinking at this point it is either a
bad chip or a bad solder joint.
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whole lot of nothing on the UART |
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I'd draw the inference that if you get the expected-snow-pre-reset, get strangeness (sometimes snow, sometimes-lines) post-reset, and don't get anything on UART, it's most likely that the "CPU" area is where you have a problem (so: prob not video chips or UART chips). Some things I'd suggest checking:
I've got a working machine; if there's anything I can measure for you for you to check on your machine, I'm happy to. |
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all great ideas
I think I'll just have to check thru each net for continuity, must be a bad joint in there somewhere |
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@joelburton what resistance to you measure across the 5v and ground header pins on the 2x3 power connector when the power is not connected? |
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~2 megs, @TwoPigsToTheWind |
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Thanks @joelburton, I'm getting about 30, maybe there's a bad cap |
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@joelburton pin 22 on U31 and pin 30 on U43 are reading 5V when power if first connected and then 2.5V at after reset. I assume the 2.5V is what I"m seeing as the average of the high and low as the U34 RAM and U36 VRAM take turns. Does that look about the same on yours? Listed bellow are some other voltages coming off the expansion header, maybe if we can identify a discrepancy it will help narrow down the issue. The power on figures may be the more useful ones for comparison. Once your machine is reset and starts running code properly the average voltage(frequency of state change) of the pins listed bellow is likely dependent on the code being run and should differ from my stalled out non-booting system. RO 1.5 @ power on & after Reset |
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@joelburton I picked up a 4ch scope this weekend, any suggestion on what to probe first? Picking this project back up after a few months away. |
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Hi Joel, although the community has built quite a number of Minimal 64x4s successfully now, there have been issues with "budget" ICs. The design uses the ICs to their full capability, so timing becomes critical quite easily. I think it makes sense to start further debugging after you made sure you have only used new parts from quality suppliers (like Mouser or such) for your built. From the failure mode you have posted, I'd guess the CPU gets stuck during the boot process copying its OS code from FLASH to RAM. I'd start with swapping U24, U19, U6, U7, U2. Good luck! |
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@slu4coder Certainly up for swapping the ICs listed above, looks like two of the '161s, a '245, and two '32. All the parts on the board are from Mouser or Digikey so generally quality suppliers. There's always a chance that one or more of the ICs have some ESD damage. Might just need to get a chip tester to look for duds. Are there and probeable signals related to the boot process you'd suggest I take a look at under the scope to try and narrow down the source of the issue? |
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Unfortunately, I can't point you to a specific signal. It is more the relative timing between different signals that may cause problems. Swapping some ICs seems a good starting point. |
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recently finished assembly. Have already checked for broken pins, backwards, or misplaced ICs and rewrote the 4 flash ICs. Any suggestions as to what to check next?
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