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Thread: Next Challenge: Hyperion that won't display text

  1. #1
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    Default Next Challenge: Hyperion that won't display text

    I feel like I'm ready to dive into this. To refresh: the Hyperion I have works perfectly in most aspects. It boots from boot disk, is responsive to keypresses, etc. I can put in a bootable Kings Quest disk and everything works great - internal and external monitor are nice and sharp. *But*

    When in text mode- nothing. Bright orange screen. No text at all.

    Doing lots of research, it seems this is a common issue that befalls lots of Hyperions. I suspect most of the ones I've read about have the same issue.

    Here is the block diagram for the display board (thanks snuci for posting this): hyperion-display-block-diagram.jpg

    So if I'm reading that right, low/hi res graphics are almost a separate thing from text. Since we know low/hi res graphics work, we can assume things like the CRT itself, sync, memory, etc all work.

    So I feel like the issue is in the char gen somewhere. Here's the schematic for that: https://drive.google.com/file/d/1G1a...ew?usp=sharing

    I'm thinking I should start with the obvious - check power first. Then maybe poke around the super and subscript logic and kind of work from there? I just want to make sure I understand the flow of things and which direction to work from. I'm really hoping the chargen EPROM isn't dead... don't know of any dumps of that... so I figure I'll start with the basics first.

    Unfortunately Dynalogic soldered most chips in so this isn't going to be very much fun at all, esp. since the way it's held together with screws and standoffs is a bit of a bear.

  2. #2
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    Okay, so I did a bit of tracing with my logic probe. Here's what I found.

    Starting at U6 (attribute decoder), I can see pulses/activity coming in on LAT0-LAT7. I can see pulses going out on FAT0-FAT7. I've followed FAT3 and FAT4 up to U1 (7474) and can see them pullsing the DATA pin, Pin 2. I can see a clock signal on pin 3 of U1 also. The SET pins on U1 are High, the RESET are low. There is nothing coming from Q1(? or 2?) pin 5. Pin 5's output goes to B1 of the binary adder (74LS283) at U2. I can see other 'data' or pulses on the other side of that adder (A1-A4), but nothing on the B side. If I understand correctly, a binary adder takes binary inputs from A and B and creates sums from them. So I'm wondering if something is going wrong with the 7474, and thus the binary adder isn't getting half of what it needs to perform?

    Really wish the 7474 weren't soldered in.. would be an easy one to check.
    Last edited by falter; December 2nd, 2018 at 02:03 PM.

  3. #3
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    Swapped out the 7474 ... definitely getting some pulse on pin 5 now. Nothing onscreen yet.. but I sort of jury rigged things by snipping off the old 7474 and attaching this one to the legs. Might not be secure on every pin. But I am definitely seeing a change, so that gives me inspiration to pull the boards apart and sort this.

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    Okay so my next suspect is this PAL10H8 at U6. If I'm reading the schematic right, pin 12 of U1 connects to 'FAT4', which is driven off pin 15 of U6 (a PAL10H. If I've got this right, FAT4 should be driving the DATA pin 12 of U1 (7474). I've confirmed these are connected with a resistance check, but yeah, there's no activity there.

    Now, I don't understand the PAL10H8 at all, and I might be reading the schematic too simplistically - but it seems like LAT4 goes into U6 at pin 5 and comes out as FAT4 on pin 15? Does that sound accurate to anyone in the know? I'm definitely seeing pulses at Pin 5, but no pulsing of any kind on Pin 15. So I'm wondering if I've got two bad chips here.. one 7474 at U1, which seems to be confirmed, and possibly this PAL10H8. I just don't know if it's as simple as I imagine with Pin 5 driving output to pin 15 or if something else has to happen and maybe some other IC elsewhere isn't driving something right with U6.

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    I'm starting to think I may have an issue with this SMC CRT8021-003 chip. I've been probing pin 1 (which on the schematic, says VID.. I think that's the video out signal).. my probe says it is high and cannot pick up any data or anything flowing through (no pulses). It goes to a 7474 at U49 and there are no pulses coming off the Q of that either. I'm going to try to find a replacement for test purposes but not much luck so far. If anyone out there has a working one please PM me, I'd like to buy.

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    Well, I've made *some* progress! I think.

    As mentioned I have been zeroing in on the 8021-003 chip. I had noticed pin 1, the VIDEO pin seemed to be 'stuck' high and there were no pulses or 'audible' activity coming from it on my logic probe. As an experiment, I clipped pin 1 off to confirm that the 8021 had nothing to do with graphics. I was half right... doing that caused the graphics to lose their quality.. it was like shifting down from CGA to something worse. Could still make things out on my Kings Quest screen but it was darker and missing lines.

    Anyway, I resoldered pin 1 back together again. I powered up, watching with my logic probe. All of a sudden, there's pulsing going on! Like really fast, data moving through! I look around front, and I've got a cursor!! It's not blinking, but it's there!

    I let KQ2 boot up again and graphics were back to normal. I shut down, pulled the KQ2 disk out (there are two disks.. the boot disk and KQ2 itself). The cursor moves! The machine is clearly sending out prompts, although nothing is actually appearing!

    So we've got cursor, but still no text. I'm going to try an actual Hyperion DOS disk just to confirm there isn't something about the generic PC DOS disk that isn't working with the Hyperion. But yeah.. I don't know what I did.. maybe the heat of the soldering iron shook something loose in the CRT controller?

  7. #7
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    Hi Falter,

    I wish I could help but I have two Hyperions that do not show anything on the display. Thankfully I do have one working one. I am watching this thread with interest.

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    Yeah there are quite a few Hyperions out there with this affliction and they all present the same symptoms. Have you tried booting your no display ones like I have? What I did was make two disks.. one a DOS boot disk in Drive A with autoexec that calls SIERRA.EXE on the second disk in drive B, which is just a copy of the first disk of KQ3. That confirmed that graphics were working, just not text.

    My gut feeling is this is going to turn out to be a weak-link IC... like the TED chips in the Commodore 264 machines... a chip that tends to fail after x number of years. Right now I am strongly suspecting the attributes controller (the 8021-003). I am just going over the circuit description and checking anticipated signals one more time before I pull the trigger on $100.

    You or someone with a working Hyperion should probably dump the EPROM for the char generator, if it hasnt been done already. That's another suspect. But right now I'm zeroed in on the attributes controller.

  9. #9
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    You guys do know that there's a NiCd battery in there ready to eat up your main board...

  10. #10
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    Quote Originally Posted by MikeS View Post
    You guys do know that there's a NiCd battery in there ready to eat up your main board...
    The white one shown here? Yes. Surprisingly in good shape in all cases I've seen.

    http://vintagecomputer.ca/wp-content...behind-CRT.jpg

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