justacruzr2
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Posts posted by justacruzr2
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Thanks, any info can possibly help. I will be getting back to mine during rainy days. i have been working on my car projects, especially a Suburban and a diesel Silverado, that have taken up a lot of my free time, trying to get ready for the holiday trip we took. I have several hardware projects to finish for the TI and Geneve, IDE, SAM, Corcomp repair, Geneve repair, and so forth.
BTW: Did you happen to have a BOM for ordering, I have ordered some of the parts but not all and if there is a BOM available, I would just order all from one source to have everything there on hand. Thanks.
Sounds like your repair list overfloweth. Good luck with all of it. All the general purpose ICs and transistors I got from DigiKey. Some of the caps and resistors I had on hand. The rest I got from various sellers on eBay. There wasn't one source for everything and it probably cost me close to $100 to rebuild the card. Not cheap but what's the alternative? A good CC9900 on eBay, when one comes up, sells for much more than that. No real good solution I'm afraid.
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Yes, I am and was, till I got pulled into other directions, just thought you may have some more insight.
I can add a little about the details of what I did and what I found. I replaced all the chips on the card except the ROMs and the PALs. They were OK. I replaced the 9901 although I'm sure it was OK as I had tested it with another known good 9901. I know the 7406 was bad and maybe the one next to it (can't remember it's number...maybe 7438). I also found several caps that were bad. They had dark brown spots on them that suggested they overheated and weren't noticeable until I looked at them with a magnifier. I replaced all the caps just to be sure. Also all the resistors, diodes and transistors. I didn't replace the crystal or the LED. That's about it...hope that helps.
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Can you elaborate on what was spiked on it and how you fixed it, I haven't had much time to work on mine, but when I do I want t cover all bases. Thanks
Not sure if you're talking about the disk controller card or the floppy drive so I'm going to assume you mean the disk controller card which we discussed months ago. All I did was just rebuild the card since I don't have any technical equipment, other than an ohm meter, to track problems down. I thought that was what you were doing too with your CC9900.
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A BIG thanks to all of you. And it's great to see 100% concensus.
@ Stuart
Thanks for answering what was to be my next question. I do understand how to translate the markings to the value but was not sure if it was expressed as micro farads (uf) or pico farads (pf). Thanks for clearing that up.
@ Ksarul
Definitely is my intention and the ones in this photo too (even though they don't look bad) which DigiKey identified as polyester film caps. DigiKey was unsure about the ones that all of you identified. Probably because as CC Clarke says they have been largely eliminated so they don't see them anymore. These drives are 31 years old and need some freshening up as long as I'm working on them. Actually I'm working on 2 drives. They both took a spike from a static discharge along with the disk controller. The controller I already repaired and tested with a known good drive and it's OK (the CC9900 we were talking about months ago).
@ CC Clarke
Thanks and if I can't get polystyrene from DigiKey I'll go with the polyester (mylar) as you suggest.
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Can any of you electronics experts out there identify what type of capacitor is shown in this photo. This is the main board in the floppy drive I'm repairing and I would like to replace it with the correct type. I know it's not ceramic disc, electrolytic or tantalum. I believe it's some kind of film type....but which? And it's clear to see that the cap in the lower right corner is blown. The others may be compromised as well. Thanks for any help you can provide.
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A cheaper alternative than the MG eproms is to simply press the space bar twice. This will land you at the TI menu. This was a known workaround for the software that would not work correctly from the CorComp menu. Try this first before you spend money. I can not be sure that this method works for everything but it does work for everything I have.
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Sorry to hear that. I purchased many different things from him over the years (back in the day) and he was one of my trusted sellers. He always dealt fairly and honestly.
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Another good addition to the collection of documentation would be the "Hardware Manual for the Texas Instruments 99/4A Home Computer" written by Michael Bunyard and released in 1986. It is generally referred to as the Bunyard Manual. Michael Bunyard was a Senior Member of the Technical Staff at Texas Instruments for 16 years. The manual is a technical manual and covers all the hardware TI released for the the 4A including the console. It also includes console schematics. There was also a "SAMS Computerfacts" Technical Service Data for the 4A which includes schematics and service diagnosis procedures.
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Thought I'd add this for what it's worth. If you like the feel of DOS there was a DOS system released for the 4A called Command DOS. It was written by Monty Schmitt and released by Ryte Data. I have this and it works well and is a fun way to interact with the 4A
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What kind of drive?
Fujitsu M2551A drives. These are the early models (bought from Triton) that don't have any additional numbers after the model number. Later ones have an "08" or "26B" after the model number and the main board is slightly revised and not compatible with the earlier model.
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What is the issue with the drive(s)?
Actually it's 2 drives. They took a hit when the FDC crashed and took one of my floppies with it. The drive lights come on, the disks spin, but they don't read/write.
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Anyone know of someone or someplace that does floppy disk drive repair (reputable of course)? It's a bit more complicated than FDC repair and I'm not having any luck doing it myself.
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This will make you cry. I bought an extra PEB (and some other things which included the European version of the Starter Pack 1&2 and the Game Writers Pack !&2. Not sure but I think these were only released in UK) when Triton was going out of business. They were selling the PEB, brand new in sealed box, for $50.
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Got it....
Yes, that is the way to read it, and if you can bring up the photo full size, of the two pots, you'll find the answer to the second question. The number 3 is on the left side front face of the pot, 2 in the middle, 1 on the right.
Got it...Thanks.
"The one next to the two eproms, mine did not have any jumpers, but in other photos, in my archives, I see jumpers in several configurations, is this why my TI kept coming up with a cyan screen, was this tear down preventable?"
I've seen the same thing in another photo. But mine has only 1 jumper between pins 2 and 3 on the lower 3 pin jumper pack. Those other jumpers in other photos may be for testing purposes. I don't know for sure. All I can say is that my card works except that it doesn't recognize a disk in the drive. I doubt that's the reason why. There are still some minor unresolved issues like setting my trim pots and until I have addressed all those things I'm not pointing the finger at the jumpers.
"The area where the trim pot is marked, what is the value on your pot, mine keeps fluctuating around?"
Haven't done mine yet. You do have to do the procedure correctly to be able to adjust it correctly. The master Reset has to be pulsed first before you jumper the pins and put it into test mode. The better and correct procedure is in the datasheet for the WD2793. I downloaded it and read it and it's very thorough. The setting that other fellow who built his own disk controller card is incorrect for 5 1/4" floppies. He said to set the 50K pot to 250ns but he didn't mention that setting is for 8" floppies. The datasheet says 400ns for 5 1/4's. I recommend you download that datasheet and read it. The procedure for setting both the 50K and 10K are there. Afterwards they should settle down and give a steady reading.
"And what is the purpose of the two caps on the marked regulator, for decoupling or smoothing out of the by-passed voltage?"
Basically you are correct. The answer is actually in this thread a page or 2 back.
Hope that helps!
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Is the way to
Okay I got some readings on the to variable pots, the 50k: 3-----14.36K----2------36.8K-----1. The 10K: 3-----1.60K----2------8.99K-----1. In the picture, the 50K is on the left. Also here are a couple of slightly better images of the card as I rebuild it.
Is this the way to read that: "between pin 3 and pin 2: 14.36K; between pin 2 and pin 1: 36.8K"? And if so which pin are you calling pin 3?
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I am still going to get readings from both of mine. I have ordered replacements parts from Jameco and will be rebuilding it as soon as everything shows up. I seem to have misplaced the contained\r holding the original parts though, that's why I have not yet gotten the readings
Since my original reply some of the details have changed as per the above. So be sure to use that info also. And I have to correct myself. When you take the readings I suggest checking between the (+) pin and the Wiper (middle pin) since it's the middle pin that's connected to pin 18 of the WD2793. The 10K pot seems to be not critical as per above.
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OK.
The two pots also get a mention in the FDC data sheet - there's a copy at [http://lab.nethence.com/frederic/Tavernier/Driver/WD2793%20datasheet.pdf]. For the WPW, it seems a little vague as to what value you need (but reading more of the datasheet might help - I only had a very quick skim through).
I'm going to check that out. Also got a reply from him. Here's what he said:
It’s been a long time since I did that board and have forgotten much of the details. I do remember that (at least for single density) the settings are really not critical. Start with the trim in the middle of the pot and do disk reads watching for errors. If however you have a scope you can fine tune it as I describe (referring to the 50K trim pot). The second pot is for write pre-compensate and except for very old 8” drives can be ignored (referring to the 10K trim pot). The WD data sheet really explains well the setup.
So according to what he says, the 10K trim pot for write pre-compensate is not critical. I suppose that setting it in the middle of its range should be sufficient but I will also look at the FDC data sheet for any additional guidance. Thanks again Stuart.
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OK...here's what I found when examining the WD2793 circuit traces on the CC9900 board and comparing them with the pinout chart and the instructions given at the web page:
http://www.s100computers.com/My%20System%20Pages/ZFDC%20Board/ZFDC.htm#Data
Pin 18 (RPW - Read Pulse Width) is tied into the 50K trim pot (W503). This is the one he uses to adjust the 50K trim pot as mentioned in his instructions. As viewed from the front (component) side of the board, the right pin is voltage (+), the middle pin (Wiper) is tied to pin 18 and the left pin is ground (-).
Pin 22 (TEST) is tied into the dual pin jumper that is just to the lower right side of the WD2793. This is what he refers to as JP4 in his instructions.
Pin 29 (TG43 - Track Greater than 43) has a single pin jumper tied into it (about mid point on the right side of the WD2793). Used to observe the continuous pulse.
Pin 33 (WPW - Write Pulse Width) is tied into the 10K trim pot (W103). As viewed from the front (component) side of the board, the right pin is voltage (+), the middle pin (Wiper) is tied to pin 33 and the left pin is ground (-).
This is probably enough information now to be able to adjust the 50K trim pot but there's no information as to how to adjust the 10K trim pot in his article. I did get his email address and I'm going to send him a message and ask him about this. His board uses 2 trim pots also and maybe that 2nd one is for the Write Pulse Width. Thanks to Stuart for hunting down the info on the 50K trim pot. -
If you look at this page ...
[http://www.s100computers.com/My%20System%20Pages/ZFDC%20Board/ZFDC.htm#Data Seperator Adjustment] hyperlink not working - copy/paste the bit between the []'s)
... it has the procedure for adjusting the two pots. But you need to be able the program the FDC to a certain mode though (possibly a bit of assembly) and you'll need an oscilloscope or logic analyser. Or a trial and error approach seems possible ...
Thanks for the info. At least I now know what these trim pots are there for. One is a 50K pot like he uses on his board and the other is a 10K pot. I probably shouldn't have touched these until I replaced everything else and tested it. Only if it was still not working right should I have tried replacing these. Not having the fancy equipment leaves me with the trial and error method or maybe I can contact Richard Bell and see if he can do the adjustment.
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It's to late for that, though I still have the hardware. Do you think I would get a good reading out of circuit?
I'm assuming that means you already removed it. No matter...also assuming that it's being supplied with 5 volts when on the board so you still should be able to see what it's allowing to get thru off the board. The middle pin is the wiper so you want to get a reading between the 2 outer pins. Because I'm not sure which direction voltage is being supplied to the trim pot (which outer pin...unless the trim pot has a "+" sign over one of the pins) you may have to try both ways. Try supplying 5V to one side and take a reading on the other side. If that doesn't work, or you get an odd reading, try reversing the test leads. Also assuming your tester can supply 5V thru the positive lead.
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I decided last night to strip my 9900 down to the bare board and rebuild it with all new components to include machined sockets. I will be scanning both sides and using one of the electronic CAD packages to produce gerbers down the line. The only used stuff will be the hard to replace chips. This should tell us for sure if it is a PAL issue or not.
That's basically what I did too. Everything on my board is new except for the PAL's, the crystal, the ribbon cable socket and the 8 position DIP selector. I was able to find everything either from DigiKey or on eBay. One suggestion....before you remove the trim pots take a reading on them so you can adjust the new ones (if you plan to replace them too) to the same value. I neglected to do this with mine and now don't know what they should be set at. This could possibility be part of the problem I'm having with the card not recognizing a disk in the drive. If you do take the reading would you let me know what it was in a post and I will set mine to the same value. Thanks.
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Yeh, that may be the case, My thinking is that the PAL's(at least the one directly under the eproms) are used in the the process of the TI 'seeing them', but I don't know enough about it for sure. And it could be a bad solder point, blah,blah,blah, etc.
I remember doing some work on it back then, but then abruptly packed away everything, as my dad and I were at odds at the machine shop he owned, about a bad family member issue, and I moved back to S. Georgia, where I am today.
So after all this time, I'm trying to get my stuff back into useable shape, but I have a lot of irons in the fire, projects(TI, PCs, cars), work, and my wife had been a unwilling participant in a car accident 3 months ago, so trying to plow through it all.
I will work on something for awhile then put it down and go to something else another day, because what I had been trying to do wasn't working at that point.
Case in point, my IDE cards, I have built them, but having issues with them( used the hot plate soldering technique, so trying to debug).
Do the same thing myself. When something isn't going exactly right I'll take a break from it. Found that coming back to it refreshed usually makes the difference.
I'm curious....you mention cars as one of your projects. Are you talking about restoring older cars like from the 50's, 60's and 70's? Have 4 that I'm doing myself. Currently working on my 70 Plymouth Belvedere (the cheap RoadRunner!). Have been enjoying this hobby since I was 15. Hard to find the time sometimes though. Patience, patience, patience.
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Oh yes, it worked fine in both the TI and Geneve until one day it just stopped working on the TI, I can't remember if it locked the system up or just gave the cyan screen that it does now, that was 18 years ago. It still works fine on the Geneve, I just booted the night before last on my Gotek floppy emulator and a 16GB thumb drive and have booted in the last few months from it with 3.5 floppies. As for your floppy drive not being seen, I experienced this with my HFDC and some of my old drives, maybe not the same problem, but I think it was the drive's' fault. Also a similar experience with the 9900 CES till it gave me the same cyan screen I have described earlier.
OK then. I'm going to undo those 2 mods and see what happens. My only other thought on it is maybe the Rev A card is a better design than the early model card. Currently my PEB has 1 bad drive attached and 1 good one. The bad one is one of the originals I bought that took a hit when I used that WD2793A by mistake. The other one is one I bought off eBay so I would have one good one for testing while repairing the CC cards. I also have a 3rd one that was actually the 2nd drive in the PEB and it took a hit at the same time as the other one. That is the one I'm currently trying to repair. If successful I will then repair the one in the PEB too. Anyway, the Rev A card does recognize a disk in drive 2 with the one bad drive attached while the early CC card does not.
Funny about your card working in the Geneve but not the TI. Makes me think that maybe your PALs aren't bad. Don't see how the Geneve could bypass the PALs which are essential to the cards proper functioning. But I could be wrong.
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Yes, I agree. I believe that burning another eprom set will not fix the problem. I have tested all the logic chips, changed out the 9901 and the 2793 FDC and examined my traces with a flashlight.
That only leaves bad solder joints, caps, resistors,a transistor( to be honest, I haven't checked it yet, will do tonight),crystal, and variable resistors(did I already say resistors?) .
Transistors are susceptible but I think the only transistor on that board runs the LED. Also look for any brown discoloration on the caps. I had several on mine that had brown spots on them and that indicates overheating. Also had 2 bad resistor packs (SIPS). Very doubtful that a crystal would go bad.
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Help identifying capacitor type
in TI-99/4A Computers
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Same here. Currently working on a vintage cassette deck. Anyway, the CC9900 I was talking about was the Rev A model. I also have the first model and rebuilt it also but I haven't adjusted the trim pots yet. Still have the readings you took on yours before you disassembled your card so I have the specs to do that when I get around to it. Was more interested in getting the Rev A card working first so I could start repairing the floppy drives. Need a working card first before I can determine whether repairs to the floppies were successful. Keep at it....you'll get it done.