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Macross_VF1

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Posts posted by Macross_VF1

  1. Posted

    So that's what silkscreen means. Thanks for explaining it to me, much appreciated.

    Anyway, back to the machine. I think I've identified all the components between pin 3 of Sally and pin 17 on GTIA ie the trimpot and its associated circuitry.

    C44 on the Atari 130XE diagram is C19 on my machine.
    R45 do not seem to exist on my board.
    C45 = C16
    R35 = R14 (obscured text, between CR2 and R15)
    CR2 = CR2
    CR3 = CR3
    C46 = C14
    C47 = C15 (obscured text, between CR3 and R12)
    R47 = R12
    C48 do not seem to exist on my board.

    That should hopefully make it slightly easier to figure out what's what.

    Of note is that I've checked some of the voltage levels displayed in the Sams schematics and it's not looking good.

    Between Pin 3 of Sally and C44 I'm getting about 2.5V and should be 4.8
    The trimpot's range should be between 0-8.5V but is between 0-6.9V
    I should be getting 5V between C45 and CR3 but instead I get 6.7V

    Also of note is that R36 is marked as 680 Ohm in the schematic but is 680k Ohm on my machine. Might it possibly have been upscaled to compensate for the removal of R35? With R35 gone it's the only source of +5V for this part of the board.

    As for the PSU, I'm currently using a USB charger that provides a very steady 5V, instead of the brick PSU I had originally borrowed from my 600XL. I have pretty much ditched the old PSU after being told it's unreliable as fudge.

  2. Posted

    Time for a report. The sockets I've installed have been verified to be connected to the correct points. I've even tested that the chips make good connection with the sockets themselves. I have also spent some time looking over the entire bad for potentially bad solder joints and I did find a lot that I had to touch up.

    You don't have to worry about the caps however, they were some of the first parts to be replaced and I quadruple checked the type, voltage, capacitance and polarity when I installed them. There are still two Non Polar ones I haven't replaced however since the replacements turned out to be about four times as large as the original ones.

    Since we have concluded that the XEGS schematics are mostly incorrect, I've instead tried to manually follow the paths to and from the trimpot. So far I've identified that it connects directly to pin 17 on GTIA and through a few components to pin 3 on Sally. I don't know if that's useful information however. Should I perhaps try to replace it just to be sure it's not bad?

     

    Probably not. What we have is only one schematic by a
    third party and he had a bad habit of putting the
    wrong number on just about anything at random. So
    combine that with the wishcasting of thinking this is
    using the same numbers as the 130XE and is shades of the
    800XL and 130XE duplicity where that train of thought is
    valid, this creature however is another bag of worms entirely.

    We are at the mercy of what we can figure out armed
    with only the above knowledge. Don't believe the schematic
    until you can PROVE it right. In the meantime trust your
    eyes and verify, verify, verify.

    So verification from an actual XEGS board shows the
    proper suspect 3904 NPN is Q1 as silkscreened and quite
    close to the color trim pot silkscreened R13. Cancel
    previous advice for Q5 as per schematic and do Q1 as
    per silkscreen instead.

     

    Here my normally excellent English knowledge fails me. I can't for the life of me understand what silkscreened mean in this instance. Anyway I've replaced Q1 and no improvement.

  3. Posted · Edited by Macross_VF1

    I concur, that part of the circuit is dead and we don't

    know why yet.

     

    Might be worth replacing Q5?

    At first I was ready to dismiss this advice as I had already replaced Q5. Then I started looking closer and discovered that there are TWO Q5 on the diagram. In fact when I take a deeper dive in the XEGS diagrams I was linked to earlier, I can see that there are several missing components compared to my machine. Could it be that my revision is different? It's a Rev A by the way.

     

     

    HI,

    here is the rest of the set - i assumed you already had it but well done for getting it going without it! :)

    Could you supply me with a Rev A set of diagrams?

  4. Posted

    Alright, so that answers what I was wondering... (PAL vs NTSC)

    CO14889 - PAL GTIA

    CO21698 - PAL ANTIC

     

    So they're both PAL, not mismatched PAL/NTSC. Nice work replacing all the sockets, but in the process of replacing them a trace or through hole might have been damaged... Back to checking other things as posted previously.

     

    Have these two chips tested good in another system?

    One at a time they have but just to be sure I swapped both with the chips from a 600XL. In the 600 the chips works great, while the 600 chips in the XEGS show the same problem, ie no colour. So it has to be something other than the chips.

     

     

    That might be the most telling symptom ever.

    They always "do" something.

    Put some Deoxit or other contact cleaner on it and

    rotate it about while wet. Let dry and rotate some

    more and then see if it does something now.

    Did just as you suggested and no difference. Nothing happens when I turn the dial, neither on RF nor composite. I've measured the pot and it gives the proper resistance and it is connected to the proper components so no broken traces. That said, there might be something connected to it that doesn't work as intended.

    • Like 1

  6. Posted

    I'd check everything around GTIA ANTIC, the crystal and transistor section of the board for bridges, breaks, and cold joints, make sure all pins are in their holes and you didn't damage any pads or traces..

     

     

    double check monitor/tv cable as well...

    It does seem like I have a lot of checking to do...

     

     

     

    Is the machine PAL or NTSC?

    It's supposed to be a PAL console but this problem does seem like it could be an NTSC issue.

  7. Posted

    HI,

    here is the rest of the set - i assumed you already had it but well done for getting it going without it! :)

     

     

    I'm pretty crap at reading diagrams but I am slowly getting better.

     

    So I've checked pretty much every component that is between video out (both RF and composite) and the GTIA. I found one resistor (R80) that measures 1k Ohm instead of the described 2k and one diode (CR4) that might be faulty. I haven't been able to test the L5 coil.

     

    Just to be sure, I desoldered the 4050 chip and tested it in a 130XE and could conclude that it's not the source of the problem.

  8. Posted

    have you checked the associated components between GTIA pin 21 and the composite out?

     

    No I have not checked all the components, but with the the picture you've attached it will be much easier. Thanks!

     

     

    Have you tried adjusting the color pot?

     

    You didn't mention anything about that in your post.

    I've tried it but it do not seem to do anything.

     

  9. Posted

    After months of tinkering with an XEGS that only started to a black screen I've finally managed to get it to work!
    I've replaced all the capacitors, transistors, both RAM chips, and the OS ROM and also desoldered all major chips in order to test them in other computers. In the end it turned out that the Freddie chip was the real culprit (last chip to be tested, obviously), though I'm fairly certain the RAM chips were faulty as well.
    There is one niggle left however that I hope someone can help me with. Despite the XEGS now starting and running properly, it does not display any colour and I've tried both RF and composite. Any idea on what might be causing this?

     

    • Like 1

  11. Posted

    A while back I asked for help with a problematic Atari STFM and it was concluded that the problem was most likely a faulty RAM chip, specifically the one handling bit 15 in the memory address.
    However due to the inconsistent labeling between the blueprint (U45) and different motherboard revisions no one could tell me exactly which chip was the culprit.
    Well, I have the solution to that question now. After removing EVERY chip and socketing them, I could easily take out one chip at a time and test it by putting a fresh chip in that position. So on a C070789-001 REV.D1 motherboard, U45 is labeled U3. Figured it might be useful information to have.

     

    • Like 1

  12. Posted

     

    1st, there´s no second ROM - the left block indicates the frist 8 KByte of the O.S. ROM area between $C000 and $DFFF (incl. Selftest mirrored from $D000-$D7FF to $5000-$57FF) and the right block shows the checksum test result of the $E000-$FFFF area (also 8 KB). The complete 16 KB are located in one chip. The BASIC ROM was not recognized by the Selftest.

     

    Because the computer boots straight into the Selftest, but shows no defect RAMs, IMHO only three options possible:

     

    - Just a bloody simple short to ground (read below)

    - Defect O.S. ROM

    - Defect MMU

     

    This order beginning with the upmost probability ;-)

     

    What I mean with the first bullet point is: Check first if only a short-circuit of one of the cartridge´s / ECI´s connector pins has contact to the metal grounding plate. I´ve seen many XE systems, where the pins aren´t shortened (cutted), specially at the ECI port (2x 7 pins). Atari didn´t insert any fishpaper between the metal plate and PCB, so if there´s one of the pins too long, it might have contact to ground in same cases. Sometimes the computer doesn´t boot, sometimes this failure happens..

     

    So simply re-test the board without metal plate loose, when the XE boots into READY prompt, you know what to do - cut the too long pins, that´s all.

    I've been told elsewhere just that, no second ROM. Supposedly it's a relic from the 1200XL where the ROMS actually were two separate chips or something?

     

    Anyway, I think I've located the spot you are referring to, and no it does not seem to connect to the bottom RF shield. Just to be sure I removed the shield entirely but sadly no improvement. So yeah, the OS ROM is likely the culprit. I have a 600XL that I can swap chips with in order to test the problem, though I have to get some IC sockets first.

    • Like 1

  14. Posted

    does all of the ram tests good to the end?

    it's possible the rom is bad,

    make sure the power supply didn't cook it, test the voltage under load.

    what does the power supply look like?

    Yup, the ram checks out, I just didn't wait for it when I took the photo.

     

    The ROM does seem to be bad, so I suppose the next step will be to replace it. However, could a bad basic ROM cause the keyboard problems? I've tried manipulating the connector on the motherboard directly, thus bypassing the keyboard completely, and it doesn't seem to make a difference.

     

    As for the PSU, I'm currently using one from a 600XL. It does work as intended and outputs the proper voltage. Am I to assume that the PSU is a common failure point with this line of computers, just like the C64 PSU is known to be crap?

     

  15. Posted

    Just picked up an 130XE and it doesn't quite work as intended. It immediately boots into the ROM/RAM self test and doesn't respond much to keyboard input. In the self test it claims the second ROM to be faulty, which seems legit since I can't get access to the Basic prompt. Note that all the RAM tests out fine I just didn't wait for it reach the end in the picture below.

    However I can't reach the rest of the self test screen. Pressing option when powering on makes no difference and pressing help on the keyboard does nothing. Only reset works, though only to restart the ROM/RAM self test.
    I have one game cartridge, Moon Patrol, that works, though I can't properly start the game. Pressing 1 makes the game play itself, and reset does exactly that, though no other input seem to work. Do I have a faulty keyboard?
    On a side note, I also have three XEGS game cartridges and they do not seem to work with this system, though admittedly I'm fairly certain one is broken to begin with.
    Finally, I've opened up the system and found a few wires that do not seem like they normally should be there. Is it a factory bodge job or has someone tried a repair?

     

    tmjO1oB.jpg

     

    IbMmYMj.jpg

     

    J4ATH0Z.jpg

  20. Posted · Edited by Macross_VF1

    A few weeks ago I asked for help with an Atari 520STFM that was behaving strangely. It was suggested that it might have RAM problems so I asked around and got a disk with YAART (Yet Another Atari Ram Test) installed to test the machine.

    The thing is though, while YAART seems to work as intended, it also report pretty much everything as an error. And that just can't be right, it's pretty much impossible that every RAM chip is faulty so it has to be something else, perhaps something that connects all the chips together and coordinate them?

    I took a photo of the testing process which I have attached here, but you'll have to excuse the poor image quality, photographing an old CRT is bloody difficult.

    XyFDrmk.jpg



  21. Posted

    Sounds like a loose connection or a short somewhere. Re-seating all of the socket-ed chips or replacing the socket might help. Also check the RGB cable. As for 4 bombs I have cleared that by unplugging the ST, turning the power switch on and off several times and replugging it in again. Russ

    I've checked RGB cable and nothing seems to be amiss there, though without cutting it completely open it's impossible to tell for sure. Unfortunately, your suggestion of re-seating the chips and unplugging, turning it on and off, and replugging, didn't improve the situation.

  22. Posted

    I've found a partial solution to the image quality issue. When jiggling the RGB cable around in the socket I could briefly get a proper glitch free picture. This lead me to believe it might be a connection issue. I dug out my old CRT TV and the image is almost free of black lines, with a slight hint of ghosting. Then I tried RF on the same TV and that's completely free of glitches. Just to be sure that some of the solder points had not cracked, I de-soldered and re-soldered the RGB jack but with no difference. It would therefore seem that it's either a cable problem or a problem with the parts in the computer that output the RGB signal.

    Still, this leave the issue of why the computer can't process disks.

  23. Posted

    RAM issue perhaps ?

    BTW you can use keyboard keys to emulate the mouse with ALT + arrow keys and ALT+INSERT for left click and ALT+ CLR HOME for right click.

    Now that was useful info! Though admittedly I still don't know if I can format a disk like you suggested earlier. With the exception of the Star Blaze game, the only floppy disks I currently have are all for the Amiga and I honestly don't know if they can be formatted by an ST.

     

    Ram, MMU or Glue

    Glue? You are going to have to explain that one to me.

     

    BTW is there a picture or similar which points out where all the components are located on the motherboard?

  24. Posted

    4 bombs= illegal instruction. Did you check the floppy drive cable and tested it on your other ST ?

    Also, does TOS throw read/write errors when formatting a blank disk on your faulty ST ?

    Unfortunately I can't use TOS as I have no mouse compatible with an Atari ST.

     

    While it is true that the floppy drive cable is soldered onto the motherboard, there are other methods of testing it, such as using a multimeter in continuity mode and checking each pin separately to each solder point. I've done this and can report no errors. However I've gotten a completely new error as can be seen below. What the fudge is going on with this system?

     

     

    dIsZT6p.jpg

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