Aquarius Composite mod
20 March 2021
Nintendo Virtual boy fix
15 April 2021
Here we see the repair of this Atari XE taken on the internet as not working ...
Here it is!
the Atari XE a little dirty and above all taken as a fault due to no video signal.
Let's start with the opening of the computer which fortunately has only 5 screws on the bottom, we remove the metal screen with the usual tabs to turn so as to remove the top and bottom.
Ora viene il bello, cominciamo a vedere dove mettere le mani perché non ho trovato uno schema di questa macchina 🙁
Search for the fault
Before switching on I checked the pinout of the power connector because I saw that the cable had been spliced and I wanted to be sure that they had not reversed the polarity.
Fortunately, even if the diagram has the names of the integrated different from the board of this Rev. A, it is possible to understand and verify the signals. The connector has 3 pins connected to the +, 3 to the minus and one for the screen. I verified that the polarity was correct and luckily it was !.
The negative is on the right pins looking at the din connector with the notch up from the side where it fits (not soldering).
As usual we proceed by steps and see what could be faulty, once the power is supplied I checked that the voltage was correct and present on the integrated, in this card we do not have a voltage regulator and therefore we must be careful because it is easier to ruin.
I realized that the video signal was present, as soon as it was connected it showed a yellow / orange screen with a gray border and from there it did not go forward, neither with cartridges nor trying to put it in diagnostic mode.
Ah! I forgot first of all to always do a visual inspection to check for any cold welds or cracks, or signs of corrosion on pins or tracks.
I begin to feel if there are integrated that heat .. and .. boom! the ram was on fire !!, yes both rams were burning. At this point I turned off everything and I thought that maybe they had connected the power supply in reverse, even for a very short time the ram is the most subject to breakage.
The ram used in this computer is the same used on the Commodore 64C, in fact I had to get it from one of these because I didn't have any ..
Don't worry, no C64 has been mistreated, and the ram arrived 3 days after the replacement and now everything is ok!
After changing the RAM I try to power it again but nothing to do, still the orange screen .. so that wasn't the only problem.
Fortunately I have an Atari 800XL and so to do first I tried some chips on this other computer, well I could only test two of them because they were already on the socket and they were the Pokey (sound chip) and the Sally (6502C). Working chips! so the problem could still be on the Antic or Gtia even if the latter I gave it for good since I got a clear screen on the monitor ah let's not forget the ROM and some other logic port !.
After this I checked the signals on the bus and saw that the Sally was communicating correctly, the clock was ok and the reset signal as well, so I turned to the ROM because it was another likely to fail more often.
Checking the signals on the ROM I noticed that they were not good, they were very low and non-square shapes, so gun in hand and we unsolder this too.
The ROM used on this model is a 32Kbyte Eprom and reading it on the TL866 programmer I only had 00 00 00 00 00 well, that's not bad !.
I take an Eprom 27c256 and now? already, on the net I have not found any dump of this eprom, many replace it with a 27c128 and mount only the image of the system, but since in the original there was also the Basic and a game "Missile Command" I did not want to reduce it to just one console.
Turn that turns you also thanks to Andrew's help I got a XEGS rom from Mame and the dump was just that.
FIXED !!
With the ROM replaced the computer is back fully functional!
A nice cleaning to the plastics and the board then once closed it is almost like new !.
Here you can find the schematic of this machine
3 Comments
Ho trovato l’articolo molto interessante,infatti anch’io ho una console simile con lo stesso problema ho dissaldato
la eprom ma adesso non ho capito bene come hai proseguito e vorrei farti alcune domande:
-hai rimontato la stessa Eprom?
-se si con cosa l’hai riprogrammata?
Te lo chiedo perché per la riprogrammazione mi sono rivolto ad un laboratorio di elettronica qui a Bergamo e mi hanno
detto che non ci riescono perché il loro programma non ha in memoria la suddetta Eprom.
Grazie per la risposta se puoi
Ciao, la ROM guasta è un difetto abbastanza frequente su questo computer. La memoria non può essere riprogrammata perché non è cancellabile elettricamente e non ha una finestra per esporla agli ultravioletti.
L’unica cosa da fare è prendere una nuova ROM 27C256 (o similare) e programmarla con i dati di quella vecchia, ovviamente se quella vecchia è guasta è probabile che non sia nemmeno leggibile o che abbia valori non corretti.
Puoi trovare l’immagine da scrivere sulla Eprom in fondo alla pagina oppure cercando la ROM dell’Atari XEGS nel MAME come ho fatto io.
Una volta riscritta la Eprom, puoi usare un TL866 (anche detto MiniPro), basta inserirla al posto della vecchia C101687 che è pin-compatibile con la 27C256 ed il gioco è fatto.
grazie mille, procedo e speriamo bene……..