derkom's attempt

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derkom
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Re: derkom's attempt

Post by derkom » Tue Dec 03, 2019 7:00 pm

Okay, I have good progress to report. Not success yet, but it seems within reach.

First today I reflowed all the PLCC chip sockets, MFP, and all the RAM, and what do you know, the bus errors went away. I could see on the logic analyser that the system appeared to be running properly. One bus error on startup, followed by zero bus errors and plenty of activity on all address lines. Plugged in a keyboard and sure enough, a floppy LED! However, still just white screen video and no diagnostic cartridge output on serial.

So I reflowed pretty much everything else on the board, hoping that my video and serial issues might go away, but to no avail. Still white screen, still no diagnostic cart on serial. I should note that the serial chip I'm using is also pulled from Atarian Computing's Alpha board and is not known to work, although there is no reason to believe it wouldn't. When I ordered all my items from Mouser, they didn't have any of the MAX238s in stock. I ordered one on fleabay, but it has yet to arrive.

So, what is one to do with an ST with a floppy LED and no video output to confirm things are running? Why, hook up a floppy drive and try out an autobooting game of course! I soldered on the floppy connector, attached a floppy drive, and popped in a copy of Lotus III and turned it on, and sure enough, it runs the game. Still no video of course, but this certainly confirms that the system is indeed running.

Suggestions for diagnosing the video and/or serial issues are welcome. I figure I can look at the appropriate YM2149 pins to see if anything is being sent over to the MAX238. Don't have a clue about tracking down the video stuff. I sure hope I haven't cooked any of the SMT stuff, because I do not look forward to doing that again.

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Re: derkom's attempt

Post by exxos » Tue Dec 03, 2019 7:02 pm

Getting there :thumbup:

Can you send a close up shot of the video DAC circuit ?

Also do you get sound from the game ?
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Re: derkom's attempt

Post by derkom » Tue Dec 03, 2019 7:12 pm

exxos wrote:
Tue Dec 03, 2019 7:02 pm
Can you send a close up shot of the video DAC circuit ?
It ain't pretty (SMT is not my forte), but here you go. I've left this image quite large.

IMG_20191203_210725.jpg
IMG_20191203_210725.jpg (476.84 KiB) Viewed 849 times

Also do you get sound from the game ?
I knew you were gonna ask that. :lol: Right now my monitor hookup is video only. I'll get something audio capable set up in a bit and let you know.

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Re: derkom's attempt

Post by exxos » Tue Dec 03, 2019 7:17 pm

derkom wrote:
Tue Dec 03, 2019 7:12 pm
I knew you were gonna ask that. :lol: Right now my monitor hookup is video only. I'll get something audio capable set up in a bit and let you know.
You can prove it with your scope as well ;)

I was suggest you try measuring with your scope on the 75R resistors and see if you see something which resembles a square wave on the output.. Something like this...
DS1Z_QuickPrint10.png
DS1Z_QuickPrint10.png (40.79 KiB) Viewed 847 times
#stolenfromicky
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Re: derkom's attempt

Post by derkom » Tue Dec 03, 2019 7:38 pm

Was easy enough to hook up my speakers. Turns out Lotus III doesn't make any sound at whatever it shows first (I don't even remember), but AV-8B Harrier Assault has lovely chip music in its title screen and I confirm I've got sound. :)

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Re: derkom's attempt

Post by derkom » Tue Dec 03, 2019 8:08 pm

It occurred to me that since I've got floppies booting, I could see if it'll still boot a floppy with the diag cart in, and it does not. So it probably is running the diagnostic software, just not getting the output anywhere useful.

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Re: derkom's attempt

Post by exxos » Tue Dec 03, 2019 8:10 pm

derkom wrote:
Tue Dec 03, 2019 8:08 pm
It occurred to me that since I've got floppies booting, I could see if it'll still boot a floppy with the diag cart in, and it does not. So it probably is running the diagnostic software, just not getting the output anywhere useful.
Did you see my post above about testing the video RGB on your scope ?
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Re: derkom's attempt

Post by derkom » Tue Dec 03, 2019 8:40 pm

exxos wrote:
Tue Dec 03, 2019 8:10 pm
Did you see my post above about testing the video RGB on your scope ?
Oh, yeah, sorry about that. I was thinking (not thinking, really) you were talking about audio there. Seems like there's basically nothing on those resistors.

EDIT: Err, scratch that. I was doing something (else) dumb. Gimme a sec.

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Re: derkom's attempt

Post by exxos » Tue Dec 03, 2019 8:44 pm

derkom wrote:
Tue Dec 03, 2019 8:40 pm
Oh, yeah, sorry about that. I was thinking (not thinking, really) you were talking about audio there. Seems like there's basically nothing on those resistors.
I would trace it back then..

These are the 3 RED inputs to the DAC.

1.jpg
1.jpg (59.8 KiB) Viewed 818 times

3 RED outputs from shifter..

2.JPG
2.JPG (42.48 KiB) Viewed 818 times

Also check you have 32MHz on this pin.

3.JPG
3.JPG (26.56 KiB) Viewed 815 times
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?

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Re: derkom's attempt

Post by derkom » Tue Dec 03, 2019 8:47 pm

Okay, there are square waves on all of them.

R36 and R37 look like this:

R37.png
R37.png (103.91 KiB) Viewed 814 times

But R14 looks a bit wonky:

R14.png
R14.png (103.74 KiB) Viewed 814 times

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