Atari Jaguar No Power Fixed - Now No Sound or Video

[Horuto]

Sorry to post this, I'm sure you guys absolutely hate seeing these things, but I've been working on this Jaguar for several weeks now and am at the point where I could use some assistance. I got all the information I used to fix this Jaguar (including troubleshooting tips and double checking methods) from the AtariAge forums and think you guys are my best shot at solving this. Maybe this could even help people in the future fix Jaguars that weren't as simple as replacing 3-4 things.

So I got a broken Atari Jaguar off a guy I've know like three years, and I know he had been sitting on it for at least that long. He has a bad habit of buying broken consoles with intention of repairing them, but he doesn't even have the tools to do it. Anyway he finally agreed to sell it to me, and it was a super good deal and is one of the only consoles I'm still missing, so I wanted to start working on it right away. I have quite a bit of experience doing some basic console repairs and modding, hell I even recapped both the monitors in my arcade cabinets. Figured I had a good shot.

Plugged in a cart, turned it on, nothing. No power. Got pretty excited, no power is usually a pretty simple fix for most game consoles. Spent some good time doing my homework (mostly on these forums), and sure enough, UC38, REG1, and C134 were all blown to high hell. Someone used the wrong power supply on it (which I find interesting since he included a 1st party power supply and video cable with it... maybe he bought those himself who knows).

Anyway, bought a new U38 and REG1 off console5 and caps for C134 and C158 (just in case) off mouser since I needed caps for more Game Gear repairs anyway. Got em soldered in, turned it on, eureka, we have power boys. But the video... is just this - https://i.imgur.com/GnuJM1l.jpg

When you boot up a game, it's dark blue on black, then about 5 seconds later (after the Jag splash screen finishes I'm assuming) it changes it to like blue and tan, which I'm assuming is the game video. No sound at all.

It gives the exact same video using RF or the composite cable (for RF I'm using a TG16 cable since they are compatible). I have an official Jag composite cable for it as well as a third party one, both give the same thing so nothing is wrong with any of my cables. I have 3 games for it too, so I doubt it's any of the carts. Also does the same thing if I use a Genesis model 1 power supply (which is compatible with the Jaguar). I have to say, I'm pretty stumped, and am looking for things to test next, and where to go from here.

I did a bunch of power readings with my multimeter, and the U38 itself seems to be functioning properly, all the power readings are what they should be. C158 is also giving me the amount it should (it isn't too low). I was hoping someone could help me rule out my REG1 being the culprit. Using Pin 4 of the U38 as GND, I took power readings of all the pins. Pin 1 gives me 5V (which is correct I believe), Pin 8 gives me 11.47V (which I think might be high but I have no idea), and all the other pins give me a reading of 0V. Is this correct?

Also I remember somewhere on the AtariAge forums someone mentioned you can test REG1 by jumping Pin1 of REG1 to L7 and get audio if your REG1 is broken, and that trick did not work for me, I still don't have audio, which makes me think it's something else. The only thing I have not done to this Jaguar yet is a full recap, but I'd like to avoid that if it won't do anything. None of the caps are giving me readings that are suspect (IE, incredibly low), nor do any of them appear damaged (C134 was unbelievable obvious). I have a full chart of the capacitor readings from my Jaguar if anyone is interested in seeing it.

Sorry about the huge wall of text, I want to get in as much info as possible initially so no one is like HaVe YoU tAkEn VoLtAgE rEaDiNgS yEt?? (lol)

 

[+Stephen Moss]

 

I did a bunch of power readings with my multimeter, and the U38 itself seems to be functioning properly, all the power readings are what they should be. C158 is also giving me the amount it should (it isn't too low). I was hoping someone could help me rule out my REG1 being the culprit. Using Pin 4 of the U38 as GND, I took power readings of all the pins. Pin 1 gives me 5V (which is correct I believe), Pin 8 gives me 11.47V (which I think might be high but I have no idea), and all the other pins give me a reading of 0V. Is this correct?

What is the output voltage of the power unit when the Jaguar is off (measure at the power socket or between GND and the power switch)?

 

Also I remember somewhere on the AtariAge forums someone mentioned you can test REG1 by jumping Pin1 of REG1 to L7 and get audio if your REG1 is broken, and that trick did not work for me, I still don't have audio, which makes me think it's something else.

 

 

Well if L7 is the same place on all board revisions as it is on the schematic I have I do not see how connecting the 5V output from Reg1 to L7 (the INC pin of Tom) would give you audio, jumping to the bottom end of L29 and taking the supply for the Audio circuits from main system supply would make more sense where REG1 is blown and you are not changing it. Stuffing 5V into one of Tom's output pins could potentially damage Tom so it is not something I would do.

 

You could try checking to see if all the clocks are running and at the correct frequency however for that and many other possible checks you need an oscilloscope. The fact it is producing some video suggests something is going on however I think you are probably going to have to write this one off as without a service manual, a SkunkBoard and some test programs it would be impossible to fix as you have nothing to suggesting a possibly starting point.

Consequently I can only think of two things you could possibly do...

1) Do the touch test, are the BIOS, Tom, Jerry or 68000 getting very hot very quickly - if so they are toast.

2) Replacing/reprogram the BIOS chip in case its code has been corrupted/it has died, because if the BIOS chip is operating correctly and everything is getting power then you should at least either get either the RSOD and a roar or the tumbling letters and associated sounds.

 

Thinking about it you do not get the tumbling letters with a SkunkBoard, if that means the SkunkBoard bypasses the BIOS that could possibly be a way of confirming/eliminating corrupted BIOS as the problem so it would be interesting to know what it does with a SkunkBoard plugged in.

[Horuto]

Thank you for the detailed response. Here are my findings:

 

What is the output voltage of the power unit when the Jaguar is off (measure at the power socket or between GND and the power switch)?

 

12.55 for both.

 

 

1) Do the touch test, are the BIOS, Tom, Jerry or 68000 getting very hot very quickly - if so they are toast.

Tom/Jerry/Bios/68000 are all cool to the touch after running for about five minutes.

[+Stephen Moss]

Current consumption varies per game, a typical average consumption is 560mA so from a purely mathematical approach if the cart you were using had a typical or higher current usage then with 12.55 off load I would expect the input voltage to the regulators to be about more like 10.9 volts.

The fact you are seeing a higher input voltage could suggest that something is not drawing power so you could try checking the voltages at all the power pins of the IC's but as I said without a service manual and test programs to help guide you in the right direction finding the vault will be extremely difficult if not impossible.

[Horuto]

It's entirely possible not all of the pins of U38 are soldered in properly, I don't have any reference to know what the voltages of each one (other than GND) are supposed to be reading. I wonder if that could possibly be part of it or if I'm just being desperate and grasping for straws, I'm about ready to just order a working Jag to use as a test model.

[+Stephen Moss]

Well pins 2, 4, 5, 12 & 13 of U38 should be GND, pins 7 - 11 should be at or close to the incoming supply voltage from the power unit, provided you can measure 5V across either C150 or C174 U38 is working so it does not really matter what voltages are on the other pins.

What I was getting at in my previous post is that you may want to check that 5V is getting around the PCB correctly, if someone had blown the regulators previously it is possible that a power track may have burnt out and power is not getting everywhere it should but that is grasping at straws.

 

I personally do not think you are going to be able to resurrect this Jaguar if it has been damaged and you would be better off keeping it for spare parts. If you want to purchase a working Jag and compare voltages/signals at various points that is up to, I presume you have already tried cleaning the cartridge port and the finger connectors on the cartridge, if not you could try that but again I think it would prove a pointless exercise as if the cartridge check sum cannot be read I would expect you to get the RSOD, and if it is read I would expect you to get the tumbling letters boot screen.

 

I presume you are using a PAL Jag on a PAL TV or NTSC Jag on a NSTC TV just to rule out any compatibility issues. If you are connecting via RF check you have tuned into in to the main frequency rather than a sideband.

[LinkoVitch]

Have you checked for corrosion on any of the joints? or activity on the 68K? If the BIOS is socketted (IIRC some may be) perhaps try resocketing it in case there is dry joint.

 

If you have any logic probes or scope, could be worth checking the address lines of the 68K, see if it is at least trying to access ROM/RAM.

 

I am stabbing the dark here, sorry, hopefully it's not something too horrific to get fixed.

[Horuto]

Have you checked for corrosion on any of the joints? or activity on the 68K? If the BIOS is socketted (IIRC some may be) perhaps try resocketing it in case there is dry joint.

 

If you have any logic probes or scope, could be worth checking the address lines of the 68K, see if it is at least trying to access ROM/RAM.

 

I am stabbing the dark here, sorry, hopefully it's not something too horrific to get fixed.

I did some extensive probing (only have a multimeter so it's tough, and I am not super good at reading a schematic) and it seems like 68K and BIOS are both getting power. Some notable things I've seen so far, Pin16 on my U38 is reading 14v, which seems awfully high, considering intake is only around 12.5v. The game I'm testing with is Wolfenstein 3D.

 

Other noteworthy findings include Pin4 and 5 on REG1 reading 0 and R63 also reading 0, but maybe that doesn't mean anything. I'm trying to wrap my brain around what could possibly be causing both the video and audio to not be working at all.

[+Stephen Moss]

The circuit diagram I have shows Pins 4 & 5 of Reg 1 tied to ground so I would expect them to 0 or very close to, equally R63 is in the ground line so I would not expect to read much if anything there either.

It is possible R63 is open circuit but if that were the case I would not expect you to get 5V out of Reg1

 

The audio side is the easier to look at so if you have 5V comming out of Reg1 (measure between pin 6/7 & pin 1) then...

With the com lead of your meter on Pin 4 of U4 what voltage do you measure on pin 8?

With the com lead of your meter on Pin 4 of U5 what voltage do you measure on pins 5 & 7? (note pins 4 & 5 are power be careful not to short them)

With the com lead of your meter on Pin 7 of U10 what voltage do you measure on pins 1, 4, 5/TP15, 10, 11, 12 & 14

 

Are those measurements the same with any Audio/video/RF cable connected as they are with them disconnected?

 

 

 

[Horuto]

U4/ Pin8 - 5v

U5/ Pin5 - 5v, Pin7 - 0.67v

U10/ Pin1,4,5,10,11,12,14 - all 5v

There was no difference in the readings with/without the composite cable plugged in.

[+Stephen Moss]

An oscilloscope would be better to test these pins but as most people do not have access to one it makes things difficult so we have to rely on a multi-meter and make best guess conclusions based on what data we can get. The voltages you have provided suggest to me that the Audio power supply is OK and the Jaguar Audio is not muted thus I would expect you to get sound out if Jerry is producing any.

 

What is a possible concern is that pins 11 and 12 of U10 are at 5V, however this could just be a issue of when you are measuring them as I forgot to specify immediately after power up.

If the standard Jaguar boot screen is running a fixed value of 0 or 5V on these pins would be an problem as during the Jagaur roar and 3 seconds or so while it should be making the noise for the tumbling letters you should get a some value between 0v and 5v depending on what your meter averages it out to.

 

So during the boot screen audio output I would expect...

Pin 12 of U10 is the Left/Right channel word select so should be alternating between 5v and 0v every 16bits of audio data (meter averaging reads something in between).

Pin 11 of U10 is the clock for the I²S audio stream and so should alternate between 5v & 0v for every bit of audio data (meter averaging reads something in between).

Pins 5 & 13 of U10 are the Audio mute and should be at 5V during sound output.

Pin 3 of U5 is the I²S audio data input, you could also try measuring that to see if there is any signs of data activity (not fixed 5v or 0v), but if Jerry is not operating the audio channel select and clock it may not be sending any Audio data either.

 

If you can confirm any apparent lack of activlity on the audio clock, strobe or data lines that would at least explain why you are not getting any audio but it cannot point to what the root cause is as it does no clarify if Jerry is down or not function because it is getting garbage code/data.

 

What would be nice is if someone produced a diagnostic cart. What test it would do needs to be determine but I think on that...

a) Preferable bypassed the BIOS and then..

b) Output a Red screen with a constant 1KHz tone on the Left Channel only ,

c) Output a Green Screen with a constant 1KHz tone on the Right Channel only and

d) Out a Blue screen that output a 1KHz tone on both channels while any controller button is pressed

on a one minute cycle per screen.

 

would provide those without access to equipment some basic audio/visual operational tests and also allow for some basic multi-meter capable static measurements test on Tom, Jerry and the audio stage (Red & Green screen) plus test the basic functions of the 68000, controller ports and controllers (Blue Screen).