Total Challenge Ahead - DEAD Defender Board!

Jesse69

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I just won an ebay auction for a Defender ROM, MAIN CPU, and Interface board for $51. Good deal as the RED ROM board and Interface boards worked. But at first startup the RED Rom board gave a RAM & ROM Error Message, but after 10 On / Off startups that started good I guessed it was a good ROM Board. Now, the only bad board is the MAIN CPU Video board - it's totally dead! Upon startup the Defender gives sound but there is absolutely NO Video screen! No message / Nothing!

I'd say Defender should be among the most well documented boards to fix. Williams really wrote comprehensive Diagnostic and Troubleshooting manuals + Theory for Defender. So I gotta look things up and now put my $290 ebay Logic Analyzer to work! If this Defender board is too much for me I'll send it to Yellowdog to fix...

Anyone here ever fixed a totally dead Defender Board? A thing like a totally fried RAM chip can make the board seem dead... I wonder if I should replace all the RAM as a start...

How many member here have fixed Defender and Stargate Boards? So far I fixed 2 Stargate Boards but they didn't have major problems... just a chip or RAM replacement and then they were good...

Also got a 2nd Defender board to check... gotta do a Lithium Battery Mod to it first!
 
Hi Jesse,

Just a couple of quick tips.
1) Verify the model number of the CPU board. Many sellers on Ebay, including the one you bought that one from, don't know a Defender board from a hole in the ground. I bought two board sets from him listed as Defender boards. Out of 6 boards (2 CPU, 2 ROM and 2 I/O boards), there is 1 board positively identified as being from a Defender (a CPU board) and 1 I/O that I think was from a Defender (based on the pictures), but I won't be able to positively ID it until it is in my possession. Defender ROM boards won't work on anything but Defender CPU boards.
2) Try swapping a known working CPU into the "dead" board. I run about 30% in fixing "dead" boards starting there.
3) If you have a logic probe, make sure the reset, HALT and the NMI lines are correct. The reset signal should go low in response to the reset button being pressed for about 1 second then high (or the other way around). The NMI and HALT lines should be high (check the docs, I am doing this from memory and I frequesntly get it backwards if I don't have one in front of me :().

ken
 
Thanks for the tips, Yellowdog. I'll try changing out all the RAM and the CPU first too see if that fixes it. When I shorted out my RAM on my Stargate Rev B board it gave a totally dead video screen too. It's so totally discouraging to get an untested ebay board and they turn out all dead. Happened to me to on another ebay auction I should never have bought - 4 Stargate Defender Sound Boards shipped for $27 and they're all totally dead. 2 with dead roms, 1 with a dead audio circuit, and 2 with bent audio amplifier heat sinks. I plan to fix the 1 salvegable sound card and I just tried selling the other 3 Sound Cards for $7 but there were no ebay takers.

And then I don't think there's much profit selling working PCB boards that you fix to sell on ebay. I saw your ebay auction for a Stargate PCB set for $150 and a sound card for $40 all working and they didn't sell.

Defender and Stargate are like the beginner's PCB sets to fix since Williams documented how to fix and diagnose them well. Something like TRON would be a challenge to fix because they didn't write a diagnostics and repair guide for it with a logic probe troubleshooting chart like Defender.
 
... 1 I/O that I think was from a Defender (based on the pictures), but I won't be able to positively ID it until it is in my possession.
ken
I was watching those same auctions - for most of the I/O boards you could tell if they're Defender or not by looking for the 2 resistor networks between the ttl chips and caps/resistors at the top of the board. Resistor networks == Stargate and up.
 
Thanks for the tips, Yellowdog. I'll try changing out all the RAM and the CPU first too see if that fixes it. When I shorted out my RAM on my Stargate Rev B board it gave a totally dead video screen too. It's so totally discouraging to get an untested ebay board and they turn out all dead. Happened to me to on another ebay auction I should never have bought - 4 Stargate Defender Sound Boards shipped for $27 and they're all totally dead. 2 with dead roms, 1 with a dead audio circuit, and 2 with bent audio amplifier heat sinks. I plan to fix the 1 salvegable sound card and I just tried selling the other 3 Sound Cards for $7 but there were no ebay takers.

And then I don't think there's much profit selling working PCB boards that you fix to sell on ebay. I saw your ebay auction for a Stargate PCB set for $150 and a sound card for $40 all working and they didn't sell.

Defender and Stargate are like the beginner's PCB sets to fix since Williams documented how to fix and diagnose them well. Something like TRON would be a challenge to fix because they didn't write a diagnostics and repair guide for it with a logic probe troubleshooting chart like Defender.

You should also check the bottom of the boards for pins that are touching other pins or shorting to a trace. You could spend hours chasing down a problem and it turns out to be a bent pin.
 
A thing like a totally fried RAM chip can make the board seem dead...

Totally dead ? Like no display, no video, no video-sync nothing ? Totally dead = start at the master 12MHz oscillator and work forwards. The 7474's that make up the dividers for the various clock are notorious for going belly-up.

Get the logic probe out and start probing ;) The Defender Theort of operation guide is a must-have if you're serious about getting into a Defender repair.

http://arcarc.xmission.com/PDF_Arca...Theory_Early_PCBS_(16P-3001_300)_Oct_1981.pdf

- James
 
Yeah, totally DEAD discouraging! No video screen, sync, or message. Could be a lot of problems. It would be a Proud accomplishment if I can fix this board! Now I got good equipment at my disposal! Just gotta finish lengthening my logic analyzer probes and I'll start testing. And I got a similar logic probe that Yellowdog has - the Amprobe LP25B.

I got no test bench so my logic analyzer has to be hooked up while the pcbs are in the cab. That's why I'm lengthening my probes!

And now I'm wondering if I need to buy 3M Test Clips! http://parts.digikey.com/1/parts/389638-18-pin-test-clip-alloy-dip-30-923690-18.html
 
And then I don't think there's much profit selling working PCB boards that you fix to sell on ebay. I saw your ebay auction for a Stargate PCB set for $150 and a sound card for $40 all working and they didn't sell.

There isn't, but I'm not trying to make the mortgage or feed my family, otherwise I would have a store full of big buck boards like some of the Ebay sellers do. I just want to cover my cost and have a few bucks left over to buy stuff for the restores that I want to keep. If I can help people get their machines up and running so these beautiful vintage babies can be played with, then I am happy.

I was watching those same auctions - for most of the I/O boards you could tell if they're Defender or not by looking for the 2 resistor networks between the ttl chips and caps/resistors at the top of the board. Resistor networks == Stargate and up.

You could tell, if they weren't such crappy pictures. I think there is a good reason for fuzzy cell phone pictures, but if I let my true feelings out about certain Ebay resellers and their photo practices, I'll probably get the ban hammer.

Get the logic probe out and start probing ;) The Defender Theort of operation guide is a must-have if you're serious about getting into a Defender repair.

http://arcarc.xmission.com/PDF_Arca...Theory_Early_PCBS_(16P-3001_300)_Oct_1981.pdf

- James

As always, James has the right answer.

ken

PS: Jesse. PM me about those sound cards. I have a box of them I am finally going through now, maybe we can work out a bulk repair deal.
 
I got no test bench so my logic analyzer has to be hooked up while the pcbs are in the cab. That's why I'm lengthening my probes!

Buy a switcher for your bench, that way you have power, get a CGA to VGA adapter so you can plug in a computer monitor and build a wiring harness (or buy one from Dokert). That way you can just lay the boards flat (or mount them on a piece of plywood) on your desk and it is 100000x better than trying to debug something on a swinging cabinet door. It takes up way less room and you can actually see what you are doing that way.

Depending on your space, you may even have enough room to have a laptop handy to bring up the specs/surf for answers.
ken
 
Hey Yellowdog - my 4 Stargate Sound Cards can all be fixed but they are a lot of work! I already have 2 great working sound cards so I don't need 4 more. That's why I tried to sell 3 of them on ebay.

I should have just waited to buy a working Defender Board set from you but you were taking so long to have one. So now I probably got 2 main Defender pcbs to fix by myself, - will keep me busy and put my logic analyzer to good use. But don't you repair Defender boards for $20 plus parts and shipping? That so affordable I should jump on that but I wanna know how to fix stuff myself. This would help me in job interviews as it shows that I would be also capable in electronics... for maybe electromechanical jobs.

I lost out on your 2 Defender RED ROM ebay auctions. Did the buyer eventually pay you?

I won your Defender Sound Card auction.

All I needed was a spare board set for Defender. I got lots enough for Stargate.
 
You could tell, if they weren't such crappy pictures. I think there is a good reason for fuzzy cell phone pictures, but if I let my true feelings out about certain Ebay resellers and their photo practices, I'll probably get the ban hammer.
Hmmm, sounds like I missed an auction. :) The ones I was watching had nice pictures of each board, but he did have mixed sets - eg. Defender CPU with Joust/Robotron ROM and Defender I/O.
 
Hey Yellowdog - my 4 Stargate Sound Cards can all be fixed but they are a lot of work! I already have 2 great working sound cards so I don't need 4 more. That's why I tried to sell 3 of them on ebay.

I should have just waited to buy a working Defender Board set from you but you were taking so long to have one. So now I probably got 2 main Defender pcbs to fix by myself, - will keep me busy and put my logic analyzer to good use. But don't you repair Defender boards for $20 plus parts and shipping? That so affordable I should jump on that but I wanna know how to fix stuff myself. This would help me in job interviews as it shows that I would be also capable in electronics... for maybe electromechanical jobs.

I lost out on your 2 Defender RED ROM ebay auctions. Did the buyer eventually pay you?

I won your Defender Sound Card auction.

All I needed was a spare board set for Defender. I got lots enough for Stargate.

OK, I thought that was you. But I don't like to make assumptions.

The buyer eventually paid, but I had to file a non-pay on him through the resolution center. You have to wait 4 days, I waited 6. I'm still waiting for the negative feedback, LOL, yeah right.

The hard part with getting a working Defender board set is getting boards that are worth repairing to begin with. I have one set that is going into the Defender restore and 2 or three that are missing chips, so it makes it hard to determine if they are worth fixing. We'll see what the latest acquisitions turn out like.

BTW. It is probably not worth doing the button cell lithium mod on Defender CPU's. The static RAM that is used for Defenders pulls 10x the current that the later boards do, so it will suck the CR2032s dry in about 3-4 months sometimes sooner. The best thing is to get one of the sealed plastic battery boxes (Radio Shack used to have them) and mount them with velcro next to the CPU (you'll have to extend the little battery cables on the boxes). That way if they do leak, they leak away from the CPU board.

ken
 
Hmmm, sounds like I missed an auction. :) The ones I was watching had nice pictures of each board, but he did have mixed sets - eg. Defender CPU with Joust/Robotron ROM and Defender I/O.

No, I was mashing a bunch of auctions together in my head. The pictures in the auctions from xgengames were clear enough to see that there is 1 Defender and 1 later I/O boards hooked to a Rev D CPU and a Defender CPU with 2 Joust/Robotron ROM cards. The real test will be to seel what if any of that works out of the box :rofl: (sorry, I amused myself).

ken
 
Flowcharts to help get you started.

http://www.vidpin.com/tech_videorecap.asp

Get a logic probe and go to town. :)

They got my Defender boards breathing a little bit, I haven't got back to finish working on them though. But I went from jailbars to a constantly sweeping nice rug pattern in a few minutes or so (not counting shipping time).
 
OK, silly me guys. I pulled the board out and then discovered it was missing chip 2E, a 74LS257 Quad Data Multiplexer. Will order it from here! http://unicornelectronics.com/IC/74LS.html

Now things don't look so bad now that I know it didn't work from 1 missing chip!

Problem is now I gotta stock up on chips for Defender... did that for Stargate and it cost me $119!

I wish I knew the Lithium Battery mod was not worth it for Defender before I bought 4 of them from Riptor. Now I bought 3 of these - http://cgi.ebay.com/Williams-3-AA-S...ltDomain_0?hash=item3efccbcb01#ht_1050wt_1173
 
See post #12 from Yellowdog.

Well, that's not my experience... but perhaps not all 5101 CMOS RAMs were created alike. They should have a standby current of ~5uA, which means battery capacity is not really a factor here. A CR2032 typically has a capacity of 220mAh, which means it should be able to supply that standby current for over a year. If that's not enough for you, you could also use a larger lithium cell.
I say give it a shot and see. BTW, I have seen 5101s simply go bad....
 
Well, that's not my experience... but perhaps not all 5101 CMOS RAMs were created alike. They should have a standby current of ~5uA, which means battery capacity is not really a factor here. A CR2032 typically has a capacity of 220mAh, which means it should be able to supply that standby current for over a year. If that's not enough for you, you could also use a larger lithium cell.
I say give it a shot and see. BTW, I have seen 5101s simply go bad....
I did the lithium cell mod to the board that came in my Defender cab, and I have yet to change the battery. That board has become my backup, so it's usually not in the machine. I used it a couple of months ago and the memory was fine. I have a repair log for that machine, and the install date of the lithium cell is in there. I installed that battery in August of 2007!! Time for a battery change. :)
 
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