DavidMil

That is for the sound adjustment for differences in TV tuners to get ride of static sounds. David

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

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

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

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

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

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

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

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

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

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

What a cool thread! Thanks to everyone for posting. DavidMil

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

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?

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.

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

Can do. I'll let you know. PS. Enjoyed our chat the other night! It was a nice long walk down memory lane! David

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.

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

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

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

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

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

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

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