Newbie Defender

[Deadin60s]

Hi all, seeking assistance in restoring an upright defender to working glory. Electronics amateur but relishing the challenge - already hooked and itching to play.

Current problem relates to the ROM board, hoping someone can help. The board is an early type populated with green Roms. Is there a schematic available for these early boards?

I have the later board schematic and at first glance the differences are not obvious e.g pull up resistors R1, R2 & R3 listed 330ohm. Chose these as examples because need checking. Despite 5V supply rail pull up value on all 3 vary around 3.5V.

Overall the cab is in pretty good nick - well worth saving. The boards aren't too bad either. The loom is another matter - lots of hacks with let ins, choc blocks, twisted cons & ins tape. Thankfully most were connected to leaf switches and interlocks, board buses intact. Sorted these hacks out first and managed to stay faithful to original wiring colours - hoping to continue the faithful theme where ever possible.

Board wise, only PS board checked so far. Found 2 duff LED's (replaced with limiting resistors). Power rails checked out. Regulated +5.13V, -5.02V, +12.28V. Unregulated tad high +14.87VDC, -15.1VDC. Trans 12 pin.

Current state of play: boots to a blank white screen with 4 lighted ROM board LED's. Surmising, from past posts, tech DB, and repair logs, ROM read problem, so way forward check ROM board PIA/Decoder circuitry - hence schematic question.

Not sure whether should have posted problem under intro forum - sorry newbie error. Anyway, any advice, tips or pointers, very gratefully received. Thanks.

Happy New Year all.

 

[DanP]

Hiya, what sort of test kit have you got? Do you have an eprom reader? If so you could (carefully!) remove the eproms and read them in and verify the contents. If you have a Fluke 9010a you could verify the eproms in circuit but that's a big leap for a beginner With Defender ROM boards I've found the interboard connector cable, dry joints and eproms are the most likely failures but that's just my limited experience.

Welcome aboards,

Dan

 

[Deadin60s]

Hi Dan, thanks for the reply and tips.

Good question on test gear. Already thinking need at least a decent logic probe. Current gear: aged scope, PL154 bench supply, and various DMM's. Read about the Fluke 9010a, appears troubleshooting a lot easier with one of these. Need to read more. Check going prices and what is needed for a complete useful working model - trying to avoid a pig in the poke ebay model. Any advice welcomed.

Similarly with eprom reader/programmer. Read 2716(?) tricky for some programmers. Hoping a workround would be to source green label ROMS from members or others who have the kit.

Also read that the 30yr old interboard ribbon connector cable first best replaced. My own has one broken securing tang but continuity rings out thro' the cable. Started a search to source this 4 row board connector. Long term, best advice seems replace all board pin connectors with gold plated headers. Again wondering on sources.

Interesting your advice to carefully remove eproms. Discovering strange pull up readings, thought best to remove eproms one at time to see if pull up readings improved - at least eproms would be out should pull up resistors proved bad and had to be desoldered. Lost me bottle with the first one! Gently began to ease first eprom out of socket but didn't like feel or look of 30yr old legs. Thinking approaching a point of no return. Might be less destructive to remove resistors and measure. In all, raises the question, how far to go in board refurbishment. Gold plated headers, fresh caps, socket IC's not sockected, best practiced mods, etc. Are members doing this and perhaps offering service on a board exchange basis - just a thought.

Jerry.

 

[P-Man]

I wouldn't touch the roms just yet in case you bust the legs. Get the thing booting first, you may have a bad PIA, the four stuck on LEDs.

Stay away from the resistors and stuff, what are you doing? that stuff is rarely bad, and is going to be your last port of call.

You are suggesting a lot of unneccesary work. Nobody goes through and sockets all chips that aren't socketed. Don't fix what aint broke. Find whats broke and fix that first

Gold-plated pin headers - whatever floats your board, but you would have to replace anythign plugging into it with likewise gold plated contacts. Nobody does this, the gains are non-existant probably.

The green label roms are the earlier set, but nothing wrong with them, the rug pattern happens for longer than the red set IIRR.

Can i ask how you know the problem relates to the rom board? do you have another working rom board that you put in and the game works fine?

also :

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

The theory of operation manual contains schematics in parts that it is describing, you would do well to read it, and it'll have the schems you need.

P-Man2012-12-29 13:26:39

 

[Deadin60s]

Thanks for the sound advice Andy.

I don't actually know that the ROM board is bad. I don't have a known good one to swap out. Be surprised if there aren't problems elsewhere. After the power supply, figured best to move on to ROM board thinking it held the boot sector and it had 4 stuck led's. On reflection, guess best to first check CPU booting cleanly.

Have the pdf, thanks. Will read thro' and check things out. Certainly not planning to fix anything that ain't broke at this stage. Present goal, get it running and start shooting. (this may take sometime)

Agree previous comments suggested a lot of work. Thought that when I read about it. Granted gold plated maybe a bit extreme, but I did think long term there may be some merit in some extra work to improve reliability. The boards I have look their age, flakey springs to mind. Then again I have no experience in fixing and running these things. Faint heart never ....

Jerry.