Macross_VF1

Here's the thing with all the transistors. Before I started this topic I had already replaced the old ones. When we started to discuss the possibility of Q1 being faulty, I actually switched back to the original one. I had kept them just because I'm aware that the leg order sometimes change despite using supposedly perfect equivalents. The old Q1 is marked as 751 2N3904 and the replacement as 2N3904 R1 C. Unfortunately I don't know who made the new ones. As for the 680k resistor, should I simply replace it with the correct one? Unfortunately I don't currently own a 680 ohm resistor, the closest one I have is 1k. I don't know if this is in any way relevant but I checked all the diodes as there are only four of them. I don't know much of the inner workings of diodes but two of them gives of a strange reading. All of them gives 0.6V in one direction, which is pretty standard. CR4 and CR3 however gives 1.8V and 1.5V respectively in the other direction. O1? I honestly can't find anything marked 01. I have checked C46, which gives 5V, unless you refer to C46 on my board, which would be C14 and that gives 7V. I most certainly get voltage to GTIA pin 17 and it varies with the trimpot. How do I verify if I get any colour from pin 21? R54 gives 0,23V

Of all the boneheaded, stupid rookie mistakes one can make... Not only did I set my multimeter to the wrong setting I also put the common probe to the wrong place! Here's the updated and correct measurements. Between Pin 3 of Sally and C44 I'm getting about 1.6V and should be 4.8 The trimpot's range should be between 0-8.5V but is between 0-7V I should be getting 5V between C45 and CR3 but instead I get 5.5V Also, directly after the collector leg on Q1 there's a 2.4V indicator. I don't know if it's relevant but the voltage I got from that point is -0.6V.

Double post, please disregard.

So that's what silkscreen means. Thanks for explaining it to me, much appreciated. Anyway, back to the machine. I think I've identified all the components between pin 3 of Sally and pin 17 on GTIA ie the trimpot and its associated circuitry. C44 on the Atari 130XE diagram is C19 on my machine. R45 do not seem to exist on my board. C45 = C16 R35 = R14 (obscured text, between CR2 and R15) CR2 = CR2 CR3 = CR3 C46 = C14 C47 = C15 (obscured text, between CR3 and R12) R47 = R12 C48 do not seem to exist on my board. That should hopefully make it slightly easier to figure out what's what. Of note is that I've checked some of the voltage levels displayed in the Sams schematics and it's not looking good. Between Pin 3 of Sally and C44 I'm getting about 2.5V and should be 4.8 The trimpot's range should be between 0-8.5V but is between 0-6.9V I should be getting 5V between C45 and CR3 but instead I get 6.7V Also of note is that R36 is marked as 680 Ohm in the schematic but is 680k Ohm on my machine. Might it possibly have been upscaled to compensate for the removal of R35? With R35 gone it's the only source of +5V for this part of the board. As for the PSU, I'm currently using a USB charger that provides a very steady 5V, instead of the brick PSU I had originally borrowed from my 600XL. I have pretty much ditched the old PSU after being told it's unreliable as fudge.

Time for a report. The sockets I've installed have been verified to be connected to the correct points. I've even tested that the chips make good connection with the sockets themselves. I have also spent some time looking over the entire bad for potentially bad solder joints and I did find a lot that I had to touch up. You don't have to worry about the caps however, they were some of the first parts to be replaced and I quadruple checked the type, voltage, capacitance and polarity when I installed them. There are still two Non Polar ones I haven't replaced however since the replacements turned out to be about four times as large as the original ones. Since we have concluded that the XEGS schematics are mostly incorrect, I've instead tried to manually follow the paths to and from the trimpot. So far I've identified that it connects directly to pin 17 on GTIA and through a few components to pin 3 on Sally. I don't know if that's useful information however. Should I perhaps try to replace it just to be sure it's not bad? Here my normally excellent English knowledge fails me. I can't for the life of me understand what silkscreened mean in this instance. Anyway I've replaced Q1 and no improvement.

At first I was ready to dismiss this advice as I had already replaced Q5. Then I started looking closer and discovered that there are TWO Q5 on the diagram. In fact when I take a deeper dive in the XEGS diagrams I was linked to earlier, I can see that there are several missing components compared to my machine. Could it be that my revision is different? It's a Rev A by the way. Could you supply me with a Rev A set of diagrams?

One at a time they have but just to be sure I swapped both with the chips from a 600XL. In the 600 the chips works great, while the 600 chips in the XEGS show the same problem, ie no colour. So it has to be something other than the chips. Did just as you suggested and no difference. Nothing happens when I turn the dial, neither on RF nor composite. I've measured the pot and it gives the proper resistance and it is connected to the proper components so no broken traces. That said, there might be something connected to it that doesn't work as intended.

Here's pictures of the machine, let's determine which chips are NTSC or PAL, if any Now since I have concluded that the XEGS Freddie is dead, I had to borrow one from the 130XE I own, and that's what the last picture is of.

It does seem like I have a lot of checking to do... It's supposed to be a PAL console but this problem does seem like it could be an NTSC issue.

I'm pretty crap at reading diagrams but I am slowly getting better. So I've checked pretty much every component that is between video out (both RF and composite) and the GTIA. I found one resistor (R80) that measures 1k Ohm instead of the described 2k and one diode (CR4) that might be faulty. I haven't been able to test the L5 coil. Just to be sure, I desoldered the 4050 chip and tested it in a 130XE and could conclude that it's not the source of the problem.

No I have not checked all the components, but with the the picture you've attached it will be much easier. Thanks! I've tried it but it do not seem to do anything.

After months of tinkering with an XEGS that only started to a black screen I've finally managed to get it to work! I've replaced all the capacitors, transistors, both RAM chips, and the OS ROM and also desoldered all major chips in order to test them in other computers. In the end it turned out that the Freddie chip was the real culprit (last chip to be tested, obviously), though I'm fairly certain the RAM chips were faulty as well. There is one niggle left however that I hope someone can help me with. Despite the XEGS now starting and running properly, it does not display any colour and I've tried both RF and composite. Any idea on what might be causing this?

For me that wasn't a solution as I just can't make head or tails of the schematic.

A while back I asked for help with a problematic Atari STFM and it was concluded that the problem was most likely a faulty RAM chip, specifically the one handling bit 15 in the memory address. However due to the inconsistent labeling between the blueprint (U45) and different motherboard revisions no one could tell me exactly which chip was the culprit. Well, I have the solution to that question now. After removing EVERY chip and socketing them, I could easily take out one chip at a time and test it by putting a fresh chip in that position. So on a C070789-001 REV.D1 motherboard, U45 is labeled U3. Figured it might be useful information to have.

I've been told elsewhere just that, no second ROM. Supposedly it's a relic from the 1200XL where the ROMS actually were two separate chips or something? Anyway, I think I've located the spot you are referring to, and no it does not seem to connect to the bottom RF shield. Just to be sure I removed the shield entirely but sadly no improvement. So yeah, the OS ROM is likely the culprit. I have a 600XL that I can swap chips with in order to test the problem, though I have to get some IC sockets first.

Unfortunately I don't have any more cartridges than the ones I have already mentioned above nor do I have any other software available. It is times like this I kinda wish I had spent more time collecting games instead of just focusing on hardware.

Yup, the ram checks out, I just didn't wait for it when I took the photo. The ROM does seem to be bad, so I suppose the next step will be to replace it. However, could a bad basic ROM cause the keyboard problems? I've tried manipulating the connector on the motherboard directly, thus bypassing the keyboard completely, and it doesn't seem to make a difference. As for the PSU, I'm currently using one from a 600XL. It does work as intended and outputs the proper voltage. Am I to assume that the PSU is a common failure point with this line of computers, just like the C64 PSU is known to be crap?

Just picked up an 130XE and it doesn't quite work as intended. It immediately boots into the ROM/RAM self test and doesn't respond much to keyboard input. In the self test it claims the second ROM to be faulty, which seems legit since I can't get access to the Basic prompt. Note that all the RAM tests out fine I just didn't wait for it reach the end in the picture below. However I can't reach the rest of the self test screen. Pressing option when powering on makes no difference and pressing help on the keyboard does nothing. Only reset works, though only to restart the ROM/RAM self test. I have one game cartridge, Moon Patrol, that works, though I can't properly start the game. Pressing 1 makes the game play itself, and reset does exactly that, though no other input seem to work. Do I have a faulty keyboard? On a side note, I also have three XEGS game cartridges and they do not seem to work with this system, though admittedly I'm fairly certain one is broken to begin with. Finally, I've opened up the system and found a few wires that do not seem like they normally should be there. Is it a factory bodge job or has someone tried a repair?

No matter, I've just been told that it is a combined chip in the 1040. Anyway, I've tried swapping the PSUs and it makes no difference. Is it possible to buy an MMU from somewhere or am I SOL? Also, in order to pull a socketed MMU chip, you need some specialized tool, right?

Thanks again! You wouldn't happen to know where the MMU might be located on an Atari 1040STE rev CA4003290?

Thanks for the confirmation on the PSU issue. However, I have no idea where the MMU is located or what it looks like. I suppose it differs depending on the revision of the motherboard?

I have an Atari 1040 as well, would it be possible to switch power supplies between the units to test this theory or are they too different?

A few weeks ago I asked for help with an Atari 520STFM that was behaving strangely. It was suggested that it might have RAM problems so I asked around and got a disk with YAART (Yet Another Atari Ram Test) installed to test the machine. The thing is though, while YAART seems to work as intended, it also report pretty much everything as an error. And that just can't be right, it's pretty much impossible that every RAM chip is faulty so it has to be something else, perhaps something that connects all the chips together and coordinate them? I took a photo of the testing process which I have attached here, but you'll have to excuse the poor image quality, photographing an old CRT is bloody difficult.

I've checked RGB cable and nothing seems to be amiss there, though without cutting it completely open it's impossible to tell for sure. Unfortunately, your suggestion of re-seating the chips and unplugging, turning it on and off, and replugging, didn't improve the situation.

I've found a partial solution to the image quality issue. When jiggling the RGB cable around in the socket I could briefly get a proper glitch free picture. This lead me to believe it might be a connection issue. I dug out my old CRT TV and the image is almost free of black lines, with a slight hint of ghosting. Then I tried RF on the same TV and that's completely free of glitches. Just to be sure that some of the solder points had not cracked, I de-soldered and re-soldered the RGB jack but with no difference. It would therefore seem that it's either a cable problem or a problem with the parts in the computer that output the RGB signal. Still, this leave the issue of why the computer can't process disks.