DavidMil
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Posts posted by DavidMil
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There is no way to get to it without removing the big aluminum casting. I suppose you could snip out the resistor and solder
the replacement to the existing leads. It's about two inches in front of the right side cartridge socket. Right beside a ferrite
bead.
David
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Ok, here's what I have currently...
U2 and U3 were getting so hot that when I wet my finger and touched them the moisture started to bubble.
Also U7 (the 6532 chip) was very hot. Placing the 6532 chip in another drive yields a dead drive till the original
6532 chip was reinstalled (but no heat). The controller chip seems to have been damaged too. R56 was also
very hot! With those four chips removed nothing gets hot and I'm getting a rock steady 12V and 5V from Q8
and Q7. I've ordered replacements from Best and I've socketed U2 and U3 so I'm going to try replacing the four
chips (starting with U2 & 3) and watch to see what happens. Could the stepper motor have a short that's drawing
all that current?
David
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By 'outer' do you mean tracks 0-19, or 20-39?
Write pre-compensation for MFM (double density) operation only kicks in on tracks 20-39 to "pre-compensate" for the increased physical density on the inner tracks.
To me that behaviour further supports that the write precompensation variable resistor is too far off spec from 230ns... It's adjusted at R3, and measured at TP11 (pin 31 on the WDC controller)
It could also be that your other drive is out of spec, causing the disk to be not readable in this one...
20 to 39. But there is something very wrong with that CB. Many chips and resistors and the larger electrolytic caps start getting very warm to darn right hot
if the power is left on for awhile. I'm going to have to see where all that current is coming from. Maybe a bad vreg. The power supply is good as I've been
using it on my 850 for some time. I hope it hasn't damaged anything else. I'll let you know.
David
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Are you sure the WDC is 2733? It should be 2793 or 2797. In your pictures I can barely make out anything on that chip, I presume you're having similar difficulty. It's probably 2793, since 2797 only works with ROM rev L...
2732 eprom should be fine... it's working with single density so I'm not concerned about the ROM. couldn't hurt to try a Rev L, but unlikely it will make a difference.
The issue only impacting DD still points to the 3 adjustments I mentioned previously being out. You could try the WDC 2793 chip from another PCB to see if it helps, but make sure to put it back in it's original PCB after since the adjustments on the PCB are tuned to the chip originally installed.
I answered this yesterday but my post seems to have disappeared. Who knows, maybe I forgot to POST it after I finished. I used a large magnifier and
a set of 6x glasses and I can barely see that it is a 2793 chip. Since then I found the problem to be in the controller chip. Suspecting that the problem
was the EPROM Rev K, I swapped it out first but nothing changed. So I swapped out the controller with a 'new' chip from Best and the drive formats fine
except it was is having problems reading disks it didn't write and the other drives have problems reading the disks it formats. I took the rev L chip out and
put the rev K back in and it is better but still having problems reading the outer tracks of disks written by other drives. I'm guessing it needs to be realigned
now?
David
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I did the same mod in another of my 800's and the colors are definitely better on it too! It's just a lot of
trouble to strip an 800 down to the MB. I don't think I'm going to go through all that trouble for my 800
that I use for programing.
David
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I'm sorry to hear that - esp. while I'm unable to help: As it was already mentioned in an other thread, the shipping regulations to the US have changed and sending goods in "letter-envelopes" isn't supported anymore.
Shipping of goods for a private person is ridiculous expensive now.
So finding a contract manufacturer in the US seems to be the only viable way.
Unable to help? You've done so much already! You have nothing to be sorry about! Is shipping from all of Europe high now or is it just some countries?
Maybe a work around for shipping could be found?
DavidMil
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Well I have to admit that this mades a very big difference in the intensity of the colors! Such a simple modification
and yet it makes a big difference. Now I'll pull apart my other 800's and do this same mod.
Thank you flashjazzcat,
David
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Well, I'd have lost money on this bet... I was sure it was an problem with the transport, but when I switched it with one of my
known good 1050's it worked beautifully. And the problem stayed with the printed circuit board. So I pulled the metal housing
off and found an Hitachi HN462732G EPROM with a sticker that said, " TANDON REV K". The Controller is a Western Digital
WD2733PL-02. I've included a couple of pictures. I'm open to suggestions here?
DavidMil
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Was the mech swapped to that drive/motherboard from another drive?
That brings up a good point, Let me swap the drive mechanisms with one of the good drives and
see which part the problem follows.
Thanks,
David
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I have three 1050 drives. Two work beautifully and the third one works fine except:
It will not format disks with DOS 2.5. It formats fine with MYDOS and the other two
drives can read disks that it formats and writes in MYDOS, but it can't format in DOS
2.5. If I format the disk on one of the other drives, I can then read and write to the
disk in the third drive without any problems, and both of the good drives can read
what the third drive has written without any problems. I also ran the 1050 CPS disk
several times through the test loops without any problems. I'm stumped.
DavidMil
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What a cool thread! Thanks to everyone for posting.
DavidMil
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My print heads didn't last very long either. Seems the combs/tines are the number one enemy of the print heads. I ordered three print heads for
two different 1027's, and slow but sure after some use the print heads got caught in the combs and destroyed. I think that the print heads may
have been a bit too soft and allowed the combs to cut into them after some use. One 1027 had a completely new print wheel from Best (it took
some time and a lot of cussing to get the wheel off and replaced).
DavidMil
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My contribution so folks stop plugging mask ROMs in backwards trying to read them, breaking clips, and mangling sockets.
This is very nice work! How long have you been 'dinking' with 850's? Seems like I remember MEtalGuy66 saying some time back,
that you had completely disassembled and had (possibly) rewritten the 850 ROM?
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First of all, What is this type of socket I see on my 850? Never seen it before, looks like some kind of system to help release the chip, but I cracked it a bit on extraction... Chip markings of "C012099B 185©1981 8233" don't immediately suggest a revision, but the date code indicates August 1982...
If you put a thin flat blade screw driver under the tab and press down it will release the two little catches that you can see through the top plastic
piece (right by the tab). Once you press down and release the catches you can slide the top piece towards the other end of the socket (if the
device has not frozen up with time). Note that you can't slide the top piece back by trying to slide the IC back, because the IC is seated in the
bottom half of the socket already. With the catches released push the tab back towards the chip, then raise the IC out. It's (sorry, at this point I
got kicked out of AA).I've included a couple of pictures. It's hard to see as the top piece only moves about a mm, but you can see the change in
locations by looking at the plastic in the middle, or by looking at the location of the tab from the end of the lower part of the socket.
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I changed the middle LED to green and have the last two connected to SIO data in/out, green is in, red out. I also have data I/O LED's on one of my 1050's and my 1010. Green and orange on the 1050, blue and red on my 1010, unless it's in Rambit mode, then it's a blue/green instead of blue. But I'm getting tired of blue LED's on everything myself, but then I'm also tired of green and red. I need to install some more yellow, orange, white or other, more exotic colors...
Wow! That confused me. You could put bidirectional LED's on your 1200XL to give you even more info in the limited space. Or, if you want to do something really
confusing, All Elect. has some two lead LED's that slowly rotate between RGB. Try to keep up with that! Put some ornaments and tinsel on you computer, and you'll
want to sing Christmas carols... I like you ideas though.
DavidMil
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Doing some reading of old threads, one of the ROM differences was the ability to automatically download the R: handler from the 850 more than once. Some units would require a power cycle for it to work again.
DavidMil, since my ROM is toast for now, can you test for this behaviour with your working ROM?
And then others can test for 850's that behave differently, meaning we have 1 easy behaviour to check for a different ROM without opening.
Can anyone remember any other functional 850 ROM differences?
Can do. I'll let you know.
PS. Enjoyed our chat the other night! It was a nice long walk down memory lane!
David
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Someone was asking about the LED assembly on the 1200XL.
I found one.
Who was looking?
Bob
About a year ago I had asked about them. Best didn't have any more either. So like so many people on this site do,
I decided to make my own. I bought a program called, "PCB Wizard", made the transparency, and made six copies
on a 4" x 6" single sided copper board. Two of the boards had bad traces, but four came out nice. I replaced the
originals in both of my 1200XL's, but I still have two left myself. Below is a picture of two of the boards and an Atari
board.
DavidMil
PS. Mine won't ever break at the connector because I put through hole eyes in them.
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I have seen C012099B-2 and -3 and now yours without any rev level. Who can tell what went through the minds at Atari and their
contractors back then?
David
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Congrats to DavidMil, as he was also able to use the 8K cart trick to dump his 850 ROM, and we found the resulting code was the same as mine. His chips date code is actually a littler older, but I suspect the '-03' is just a plant/production run identifier similar to what I've seen on GTIA/ANTIC, etc rather than a revision identifier.
I think we went over this a couple of years ago.
Normally I would agree with you Nezgar, but Appendix 6 of the 850 Field service manual give info on software upgrades.
I've posted a pic of the page below. I tend to think that rev 3 was the last software upgrade that Atari did to the 850 as
chips with later manufacture dates didn't have any version listed.
DavidMil
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When I tried to remove my ROM chip, the clip shattered into three pieces. So like you I'll just replace the entire socket.
David
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Got a successful ROM dump from my 850!
Then sadly, in my haste I fell for the ol chip orientation trick, as I did not take note of the orientation prior to extraction, and it was not immediately apparent to me which way the socket was keyed.. The bloody 6507 is reverse orientation of the ROM too.. Anyhow, i got it backwards, and probably blew the ROM when I went to test it... blarg
I can send you my rev 3 chip to look at and maybe make me a copy (which I'm willing to pay you for).
David
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Looking closely at that PCB, I'm wondering if it might have been a reject as some of the parts are actually hanging off the edge (at least according
to the silk screen. Click on the top side picture and look along the break away at the silk screen for A109...
David
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Wow great link. Nice that there's assembly instructions too, would be fun to assemble one from scratch. I even have blank 2532 eprom's and learned how to program them if anyone needs.
There's enough retro adapters out nowadays, maybe I can find one that allows a 2732 to work with a stock config 850 pcb.
Speaking of which, I'm curious to collect the various 850 ROM versions, I've read there were at least 2 or 3? I have 2 850's I plan to dump their ROMs.
As far as I know there were three rev levels. I'm guessing that the first rev level was just marked as C012099. Rev two and three have C012099-2, and
C012099-3 respectively (this info is from my 850 Filed Service Manual). I'm thinking about building one from scratch since I found a PCB. I've got all the
parts except the 4K ROM. I'm going to call Best and see if Brad has any left. If not, Nezgar, can I send you my rev 3 ROM, and could you burn me a copy?
Thanks,
DavidMil
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I've always been interested in how the 850 works. I built loopback testers for the four serial ports. Believe it or not,
you can not use one loopback tester for all four ports. And I wrote a basic program to test the four ports. I've been
working (well, not for a long time) on a device that will test the parallel port, but haven't got it perfected to my satisfaction
yet.
DavidMil
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Not getting crisp white characters on TV from Atari 800
in Atari 8-Bit Computers
Posted
That is for the sound adjustment for differences in TV tuners to get ride of static sounds.
David