Jaguar repair (black/dark green screen)

[+batari]

I have a broken Jaguar on my bench. Black screen on composite. On RF it has a black screen that turns dark green after a few seconds. It was working great up until recently.

 

I've done all of the testing that I can.

 

I have a 200Mhz scope. These are the things I found (trying to be thorough so that I don't waste anyone's time.)

 

• Power light comes on, and BIOS copy appears to start after 400ms as it should.
• Regulators, inductors, low-value resistors, electrolytics, diodes, crystals all test good.
• Bus activity on RAM chips, and activity on cart enable pins (EOE0L, etc.)
• Tom chip is not activating (signal on pin 3 of U6 doesn't change)
  •  Tom is supposed to idle until after BIOS copy, so something is likely going wrong before this?
• Cart connector is fairly new and is not suspected as the problem - everything looks good
• 68000 is cold to the touch. Tom is mildly warm, Jerry is warm (not hot)
• Address and data pins on BIOS all look good, except D4-D5
  • D4 and D5 are going around 0.6v-5v instead of 0-5v.
• D4-D5 have issues on both the input and output of U26, so I suspect another source for the issue.
  • Just to be sure, I replaced U26 (74ACT245) but it made no difference.

 

So to better figure out what is happening, does anyone know what the Jag does at boot?

Does it boot to 68000 or Jerry?

Does the boot involve running code directly from the BIOS ROM?

Or does the Jerry chip use built-in hardware to copy BIOS to RAM, then the 68000 boots from RAM?

Or what? I can't find any info about the boot procedure.

 

I do have another Jag so it's not urgent, but it would be great to get this one fixed.

 

Also, I am aware of the diagnostic test board, which supposedly allows testing of controller, video, and DSP ports. However, does the Jag have to "boot" first in order to use this cart? It's not even getting to the Jaguar red screen and there is no roar sound... so would this cart be useless to me?

 

Lastly... I read on another post that although no Jaguar service/repair manual was ever created, Atari put together some "in-house test procedures." And at one time these were available at myatari.com, but now links are dead. Does anyone know what these "test procedures" are and if they would be useful here?

 

I'm willing to replace any chips if needed, but I want to be pretty sure a part is actually bad first, and not just shoot in the dark.

 

Thanks!

[+Mitch]

You can check this thread for more info about the Jag diag cart.

Mitch

 

[+batari]

1 hour ago, Mitch said:

You can check this thread for more info about the Jag diag cart.

Mitch

 

Thanks, and even better, there is a link to a thread in there that has the image of the diagnostic cart, so I will build one of those tomorrow.

 

I see that this cart bypasses the BIOS, so hopefully the Jag isn't so broken that it can't use the cart or output on the UART.

[Zerosquare]

I've not read it in detail, but RetroSix Wiki has some repair info for the Jaguar, if that's useful:

https://www.retrosix.wiki/

[+cubanismo]

I don't think you can bypass the very early stages of the BIOS. The 68k starts executing from the BIOS ROM directly using the memory controller (in Tom) initial memory map on reset. IIRC, it copies a few bytes of itself to RAM, then flips the memory controller to the regular mode where RAM/cart ROM/etc. are accessible and then jumps to a loop in RAM that copies the rest of the BIOS ROM to RAM, before it ever touches the cart and starts the whole validation process, but I may be missrrmembering some of the ordering details there.

[+batari]

The diagnostic cart I built didn't work on either of my Jags. Apparently it will not work at all without the EEPROM chip? If so I will place an order for some tonight, I need some anyway.

[+Mitch]

Did you connect it into the serial port of a PC and use a terminal program to see the output? By default it won't run any tests by itself.

 

Mitch

[+batari]

3 hours ago, Mitch said:

Did you connect it into the serial port of a PC and use a terminal program to see the output? By default it won't run any tests by itself.

 

Mitch

I didn't try that after I saw the black screen and saw something about it needing an EEPROM. But if the serial port works without an EEPROM chip on the board, I won't bother because that is all I need. I'll try it tomorrow.

 

[doctorclu]

Cool diagnostic cartridge.  Who sells them?

[+Mitch]

11 hours ago, batari said:

I didn't try that after I saw the black screen and saw something about it needing an EEPROM. But if the serial port works without an EEPROM chip on the board, I won't bother because that is all I need. I'll try it tomorrow.

 

I can't say for sure, as I have never tried to run it without an EEPROM. But I do know that the default mode is to manually run the tests from the terminal console over the serial connection. I believe the EEPROM is only used to save your settings but I could be wrong.

 

Mitch

[+batari]

OK, the cart does work without an EEPROM. I was able to get to the diagnostics screen in the terminal.

 

However, this only worked on my working Jag. The broken one is apparently too broken for diagnostics

[+batari]

I placed an order for several of the easiest-to-find chips (the SOIC '244, '245 and '374 chips), which are also relatively easy to replace, so at least I can rule those out. Then will work up to the harder stuff like the RAM and 68000. If those don't fix it then I guess I will have to try to buy the Tom and Jerry from Best.

 

Since Jags are like $500 on eBay, it's worth putting in a little bit of effort to fix!

[+Stephen Moss]

6 hours ago, batari said:

However, this only worked on my working Jag. The broken one is apparently too broken for diagnostics

There is some test software here you could try that will run on a SkunkBoard if you have one. It may not give the detailed diagnostics of the official test cart, however as the SkunkBoard fast boots the Jaguar that may skip over any BIOS issues (if that is where the problem lies) so it may be worth seeing if that will run where the diagnostic cart won't as if it does skip over any potential BIOS issue you should then be able to do some basic Video and Audio tests. 

 

I have a broken Jag that does nothing at start up, just a black screen and as that test software has separate test for graphics and audio what that did for me was...

1) The SkunkBoard booted to its Green screen allow me to see the the Jaguar was at least partially functioning (i.e. possible BIOS issue).

2) The video tests in the software in addition to the Green Skunkboard screen showed me that the Video side of the Jaguar was working.

3) The Jaguar crashed/got stuck when trying the Audio test, I still don't know what is causing it but being audio related I suspect the issue may lie either internally or externally with Jerry rather than a possible BIOS issue.

 

So although not as detailed as the diagnostic cart may if you can get it running via a SkunkBoard may be partially helpful in diagnosing where the problem may lie.

[Bratwurst]

5 hours ago, batari said:

If those don't fix it then I guess I will have to try to buy the Tom and Jerry from Best.

 

Since Jags are like $500 on eBay, it's worth putting in a little bit of effort to fix!

I would agree on the value in repair in this case, but even in matters involving much less expensive hardware I feel there is a moral imperative to keep something out of the landfill whenever possible. It may be prudent just to go ahead and pick up a spare Tom and Jerry even if you don't need them, any idea what Best charges for those assuming he has them in stock?

[phoenixdownita]

2 hours ago, Bratwurst said:

, but even in matters involving much less expensive hardware I feel there is a moral imperative to keep something out of the landfill whenever possible.

Disagree, having some room/basement full of broken stuff (not everyone has the skill or money to fix these things) is not a solution to waste management.

 

We are a weird bunch in that we really like fixing things as its own reward, but sometimes letting go is actually the better option.

 

Wrt to this Jag given the OP wants to fix it there’s not even a point in suggesting he’d just dump it, nobody even suggested it.

 

Edited May 24 by phoenixdownita

[Zerosquare]

23 hours ago, phoenixdownita said:

Disagree, having some room/basement full of broken stuff (...) is not a solution to waste management.

I feel personally offended by that statement 😠

Edited May 25 by Zerosquare

[phoenixdownita]

2 hours ago, Zerosquare said:

I feel personally offended by that statement 😠

I can send your way all the half broken stuff I am having trouble getting rid off because fomo or other nonsense my old bones can’t let go (I have been wrestling with a temperamental Colecovision for years and I picked it up for free, changed RAM, Bios, CTRL IC, controller wires, plastic, keypad, power supply …. I should have left it where it was, but I couldn’t help it, free right!?! how could I pass on it?! and I never had one growing up so no nostalgia but by god now I can have it … almost).

 

And to be realistic no matter the repairs you do they won’t make it last another 50y … so at best you are delaying the inevitable which is fine if you enjoy doing that … wrt Jag there were not that many around so .. I mean I am sure we can already find millions of broken PS2 in the various dumpsters around the world, same for the Wii etc… etc… all of the Jags combined wouldn’t make as much difference on a practical level, and I know you know it.

 

As I said, the OP has the skills, will and money to fix it and he is trying, if he fails I hope he doesn’t have to feel bad at that point to bin it.

 

I am not telling anyone to trash anything I just got tripped by the “moral imperative” choice of word.

Edited May 25 by phoenixdownita

[+batari]

Definitely not going to bin a broken Jag, especially since I saw a broken Jag sell on eBay for $180 recently.

[phoenixdownita]

1 hour ago, batari said:

Definitely not going to bin a broken Jag, especially since I saw a broken Jag sell on eBay for $180 recently.

I really hope you can fix it but yes if someone wants it for 180 broken why not?

 

I have a not so working system (not a jag) that as is seems to have sold for 500+ a month ago or so (and not just one item) … for parts, but I am attempting to repair it a trace at a time, it went from no AV whatsoever to now a flickering “something went wrong, press reset” (courtesy of google translation) sentence bottom of the screen  … but I do not have a 200Mhz scope or even a schematics of the thing.

 

Best of luck with your repair.

Edited May 25 by phoenixdownita

[+Stephen]

3 hours ago, phoenixdownita said:

(I have been wrestling with a temperamental Colecovision for years and I picked it up for free, changed RAM, Bios, CTRL IC, controller wires, plastic, keypad, power supply …. I should have left it where it was, but I couldn’t help it, free right!?!

Did you check / clean / replace the power switch?  I had one that I swore was faulty RAM, but it ended up being a dirty power switch.

[phoenixdownita]

1 hour ago, Stephen said:

Did you check / clean / replace the power switch?  I had one that I swore was faulty RAM, but it ended up being a dirty power switch.

Yup, deoxit, scrubbed etc.. now if I have the ctrl ICs one way I have gfx glitches, swapped it seems alright most of the time, ordered 2 new ones to make sure. I got a new power supply 2 days ago to replace my hand made internal one via 3 el-cheapo china ones but it made no difference.

 

But this is batari jag repair thread, no need to detour.

[Zerosquare]

@batari I have a (working) Jaguar open and an oscilloscope lying around right now, so if there are some measurements you'd need for comparison purposes, let me know.

[phoenixdownita]

@batari do you have good news?

Has the cat some more lives left?

[+batari]

On 5/31/2024 at 4:50 PM, Zerosquare said:

@batari I have a (working) Jaguar open and an oscilloscope lying around right now, so if there are some measurements you'd need for comparison purposes, let me know.

Thanks, I will post on that soon(ish).

21 hours ago, phoenixdownita said:

@batari do you have good news?

Has the cat some more lives left?

I am still waiting on the replacement parts to arrive, but I expect to get them within the next few days.