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Grumps

Is my 600XL doomed?

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Hi All

I bought a 600XL when they 1st came out. I accumulated a few dozen games cartridges, tape deck, graphics tablet, joysticks etc. About 25 years ago it plain stopped working and in went into storage as a project for when I have more time.

I now have more time and have put the old beast on test. It simply shows a red screen. No reaction to buttons or keyboard, and no sound.

So, the question is, how far into the depths can I reasonably expect to get detailed support for this, here or elsewhere?

I have got the board out and on the desk, and I have my oscilloscope probing away. The power supply seems fine, stable 5V.

I am scoping the address pins on SALLY, and even though I can assert the RST pin low, there is still activity on the address pins - but RST goes to both SALLY and ANTIC!

Also, the IRQ pin on SALLY is low. If I remove the PIA then IRQ goes high.

It'd be great to run through all of the games once more, and maybe pass it on to the next gen.

So, thanks for any help at all.

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IRQ stuck low doesn't sound right.

But if it's not going to a black screen it means that the OS isn't executing at all or very much - zeroing registers including colour occurs at a very early stage.

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if i remember rightly, a red screen can be caused by faulty OS ROM or a bad MMU. OS ROMs can be replaced by an eprom if you have a burner?

luckily the 600XL is fully socketed - do you have another atari to try them in?

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Yep, bad OS ROM is the most likely culprit of a red screen. I believe this is the same symptom if the OS ROM is completely removed too. A programmed 27C128 EPROM would is a drop-in replacement. All 600XL's have socketed chips, so if you have any other socketed 600XL or 800XL you could easily swap it into another machine to test...

 

If you don't have a spare machine, remove/reinsert all the chips in their sockets which may help if corrosion/oxidization has made any bad contacts. The original sockets are single wipe (only contact on one side) vs better dual wipe or machine sockets.

 

Next up would be the MMU, then the PIA which controls the MMU...

 

If you don't have, or don't want to invest in an EPROM programmer at this time, PM me and I could program an OS EPROM and mail it to you for about $5. I could program a replacement MMU to a GAL as well just in case...

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Wow! Thank you all very much for your responses and offers of help.

I don't have a spare machine, so that route is out for now.

I do have a programmer at work, and I have a spare 27C512. I know that's too big, but it seems pin compatible - I think.

I seem to have found the correct OS ROM file on the 'net. And I have found the PAL/GAL source. Is there a .JED for the PAL/GAL somewhere?

Thanks again.

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Yep, the 27C512 should work just fine if the same image is repeated 4 times. Possible glitchiness if it's rated access time is too fast (maybe less than 120ns?) but try and see how it goes.

 

If you have a programmer at work, you can also try reading out your original mask ROM on it as a 27C128, and see what you get. If you see data, you can compare it's checksum with known ones here: http://www.wudsn.com/productions/atari800/atariromchecker/help/AtariROMChecker.html

 

There's a REV03.ROM image here, which has some bug fixes compared to REV02: http://ftp.pigwa.net/stuff/collections/atari_forever/ROM/Rom - OS/XLROMS/

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1 hour ago, Nezgar said:

There's a REV03.ROM image here

do you know what the REV04.ROM does?

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37 minutes ago, xrbrevin said:

do you know what the REV04.ROM does?

XEGS support for detachable keyboard, and BASIC / Missile Command game select. I don't think it has much benefit for other machines compared to Rev03.

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2 hours ago, Nezgar said:

There's a REV03.ROM image here, which has some bug fixes compared to REV02: http://ftp.pigwa.net/stuff/collections/atari_forever/ROM/Rom - OS/XLROMS/

Excellent! I currently have a rev02.rom. Your link points to roms that are identical to others I found on the 'net - so that's reassuring.

I have 2 off 27C512 to try. I hope they're blank as I sold my eraser on eBay years ago :(

 

Incidentally, is there a reliable source for old Atari spares, PIA is on my list maybe. Are there such thing as spares for the other major components, or do you need to get a unit from eBay (with the possibility that they don't work either)?

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It also helps to know where you are located. It might be a friendly Atari enthusiast closer that can help you finding the problem with your 600xl.

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Best Electronics looks like a goldmine. Don't think we have anything like that in the UK.

 

Whilst routing through some old computer boards, I did find a graphics board that has 8 x TMS4464-10. Looks like I'll be doing a RAM upgrade after the machine is working again (fingers crossed).

Edited by Grumps
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No lie, what I would probably be inclined do is to contact Simius about getting an ANTONIA board to put into it.  The ANTONIA will act not only as an OS replacement but also as a RAM upgrade.  It's a win/win for the 600XL as far as I am concerned.  I have one on one of my 600XLs and it is a fantastic piece of upgrade hardware. 

 

You can send Simius a PM here :

https://atariage.com/forums/profile/26134-simius/

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The PIA is an off the shelf chip, i bought some on ebay a while ago

see here:

 

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A month ago, my 600 XL was dead as a door nail.  Today, everything is working.  If you can beg or borrow another working 600 or 800 XL, you can swap your chips into it until you have found all the dead chips.  My 600 had a dead CPU, a dead pokey and dead ram chips (plus a flaky keyboard mylar that just needed cleaning).  The only things you can't test in an 800 XL are the ram chips and the 74S32 chip.  Of course my 800XL was fully socketed which made things easy.

After I replaced the CPU and Pokey (bought both from Best Electronics for ~$40) I put a pair of 41464 chip in place of the dead 4416's and the computer booted right up.  Then I ran the three wires that made the unit 64K.

 

These little beasts are never doomed until the motherboard's cracked in two and the case is on fire.  They are really well built. 

 

Maybe being in the UK, you should contact @FlashJazzCat for help. 

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And what about the ram extension for 600xl  from Jurgen? It is well priced and it'll replaces the onboard ram chips, the delay line and the ls158s and maybe others. 

It is a good way to get 512kb quickly and resurrect dead 600xls

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As it turns out all of my EPROMs are not blank, so I've gambled on an AT28C256 EEPROM. The only difference between the 27C128 is that pin 1 is address bit 14 and pin 27 is write_enable. Both of these pins are tied to Vcc on the 600XL, so it should just appear to be a 16k x 8 ROM. My programmer will program the AT28C256 - so fingers crossed.

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15 hours ago, Grumps said:

As it turns out all of my EPROMs are not blank, so I've gambled on an AT28C256 EEPROM. The only difference between the 27C128 is that pin 1 is address bit 14 and pin 27 is write_enable. Both of these pins are tied to Vcc on the 600XL, so it should just appear to be a 16k x 8 ROM. My programmer will program the AT28C256 - so fingers crossed.

From my experience there are things that will cause bit14/pin27 to toggle, and cause the OS to crash if both halves of the 32KB EPROM are not the same, at least in an 800XL. If you repeat the same 16KB twice, you should be fine.

 

I've also used AT28C256 EEPROM's - I've had one that exhibited some odd timing issues that would present as "shimmering" pixels on text screens... Many prior posts recommend 200+ns speed EPROMS for stability, so YMMV. EEPROM's sure are nice though for their quick erase ability.

 

There's also adapters by the likes of Dropcheck or Mr Robot and others to switch between two (xx256) or four (xx512) OS's on 1 chip via A14/A15 without soldering directly to the chip.

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Thanks. We'll see what happens later tonight.

Bit14/pin27 should be connected straight to 5V, according to both the 600XL & 800XL circuits, so it shouldn't toggle. I'll repeat the same 16KB as you suggest to be safe.

200ns+? So I may need to slow the 150ns EEPROM down?

 

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Just a quick update. I took the OS ROM out of the 600XL and read it using the EPROM programmer. The contents verify with the REV02.ROM file I found on the 'net. Whilst this doesn't mean that it 100% working (it may not read at full speed), should I be looking elsewhere for my red screen fault?

How far through booting would the machine get if there was bad DRAM?

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bad RAM chip(s) usually causes the computer to boot straight into the memory self-test.

a faulty MMU can also cause a red screen tho - have you checked it already?

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depends

if it would fail miserably - then not far at all

but if it was just lightly out of specs for this machine, results would be intermediate

there is quite decent rom based test for cases like this on the forum,

you could try it first

 

one more thing

if your machine boots up, try twisting motherboard

if there will be any sort of reaction - random hangs for exaple - try to localise this with more subtle methods and then replace faulty socket

single wiper sockets used back then by Atari don't get high scores in my book

 

Edited by candle
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A not black screen is the prime clue that it's not getting very far.

Before any Ram test occurs, the IO registers are zeroed which should remove any random PM graphics glitches (occasionally show up) and set the background to black (often the Atari will start with background colour as $F0)

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How do I test the MMU? I haven't got another to swap.

I do have a scope and the circuits, so can probe around if I know what I should be looking for.

 

Perhaps I should bite the bullet and dig my old logic analyser out and put it on the OSROM and see if the 6502 actually attempts to execute any code. That'd be fun - sort of.

Edited by Grumps

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