Posts by jlopez

    I can remember when I first got signals out of my 'ALF MC16'-like circuit. It did not have the volume control connected to the frequency generators and I could only see the waveshapes on an oscilloscope. It was like magic to see the frequencies change and have the volume levels dance around at the same time. I had the advantage to have the ALF MC16 software to test the circuit.

    The first audible sound came later, but this moment to see the system work in principle with only 5 chips... magic.

    Yes, pure magic...

    Talking of software, ALF code won't work: different processor, distinct architecture.

    This is what I used:


    It's been a while since this was updated for last time. Time to remove dust!

    I've cut traces and rewired some parts to get a minimal framework to work on. Thanks stynx for your advice: it has been gold.

    First successful test:

    First test with all three channels wired:

    This is still unfinished, but I'm eager to complete it.

    I had a serious problem as I was underequipped, but now and for three months I have a working scope and a signal generator to help in repairs and projects.



    About CAS, it didn't matter until I found it matters. The clock circuit certainly has responsibility over /CAS0, /CAS1 and /RAS, but I realized that the processor also has control over those signals. /RAS is generated using a 74LS157, which selects certain clock signals but it is enabled (or disabled) by B2 (7425) which is fed with CPU addresses, some of them after the switches. Still, I think this gate is failing, because both the strobe and one of its inputs (pin 9, connected to A15) are high and according to the datasheet, input should be low in this case but is high. Therefore, it disables the 74LS157, also disabling /RAS.

    The CPU is running for short time, but long enough to erase the screen. When a pre-crtc CBM/PET powers up its vram is full of random contents. If working appropiately the CPU inits it to 0. Otherwise those values remain. When I power it up and the monitor is not initialized no values are shown, but if I turn it off and power it up again quickly the values appear for a few seconds and then black screen is displayed. If no ROMs are in place (or wrong combination of BASIC and KERNAL) the values remain displayed. I tested the reset by removing the 555 and using a wire from the empty expansion sockets to pin 3 of the 555 socket, making contact manually for a couple of seconds while the board is powered. Prior to the reset signal I have /RAS and one of both /CAS signals. When the signal is applied, it starts to generate that weak RAS... what's strange is that because between pin 3 of the 555 and the /reset pin of the 6502 there's a 74LS04 but the thing seems to react only with a low signal on pin 3 (or a high level on /reset). When that happens, the screen is erased, meanwhile the characters are there.

    Thank you and regards

    About /RAS, I've replaced G1 (74LS08) with a new one. Same result. I'll check the traces.

    I've checked both /CAS signals; the only suspect was B3, replaced with no change. After checking again B3, found it was working and that the CPU is completely still. It's strange because this 6502 is known to be working as it was tested in a 8032 flawlessly. RDY is high and Phase 0 pulses at 1MHz. What else could cause the processor to stop?

    Yes, Phase 2 looks weird. This capture was taken directly from the CPU.

    I know it's tedious, but I'm pleased to service it ;).

    Thank you again!

    Good afternoon

    This morning I was able to get a working scilloscope thanks to two of my former teachers. I've taken some measures at TP9, TP7, TP2, TP1, TP3, Phi2, R/W, CAS0, CAS1 and RAS.










    The scilloscope figures present at my docs are from the display, not from the computer itself. While some of them are fine, others look definitely wrong. As found with the logic probe a couple of days ago, both /CAS signals are permanently high. /RAS oscillates but seems to never go to low level either...

    G8, G9 replaced, no change.

    I found a broken trace between H6 (74LS107), H9 (74LS93), G6 (74LS107) and F6 (74LS107); it is named in the scj¡hematics as /RA1. After the reconnection it continues to display the same amount of garbage characters for the same amount of time with the exception that they are now semigraphic chars. Other replacements have been H10 (74LS08), G7 (74LS10), G10 (74LS00), H2 (74LS04).

    I'm feeling a bit tired, I should take some rest and continue later.

    I had to replace the 7474 on two of mine. In general I find them problematic on most boards. On one PDP11 CPU Board I had to replace all of them. Might be worth checking first.

    That's G8. With complement of rust. I'll check it first.

    Thank you!


    I've checked the board and saw G9, which is as rusty as G8. G9 is also a '74 and also has responasbilities over video. I'm thinking again that thing of the sync and if I had sync problems the monitor should have snow, but the few characters displayed are shown correctly, without flickering or any kind of displacement. G9 controls when video is shown (or not shown) which seems to describe more the failure I see.

    Thank you again

    Precision sockets are very OK.

    I think Forist meant the original ones which quality was a common sore.

    I feel relieved now...

    The bad thing is that you need to understand the schematics and the chips data sheets to check every important component complex.

    There are probably good books on this.

    Optimum would be if you can find the service manual; it would give you an easy step-by-step guide to find the problem area.

    I'm working with a printed copy of it. That's where I found it ->…ters/pet/2001N/index.html

    The monitor looks okay to me. I guess it is free-running (not synched), as it does not get a valid signal.

    The monitor is fine. It was tested and found working. Running unsynched? Good, that's really the kind of point I was seeking. The few characters displayed are seen correctly, I guess that this means that "Horz Drive" is ok and I should look for "Vert Drive". Suspects are, for now: G10 (74LS00) and H8 (74LS107); both of them in sheet 6. If found working then G8 (7474), G1 (74LS08), H5 (74LS00), I1 (74S04) and G2 (74LS20); all of them in sheet 7.

    For the testing, sync signals can be obtained at the user port easily.

    The dot after turning off is an old commodore flaw that provides for ugly burn-in holes in the screen middle.

    There are fixes for that available in the web.

    Yes, I know what it is and what it does. We call it "el punt verd de la mort" (the green dot of death) and I have other monitors that have this issue. What I didn't know is that there is a fix for them. I searched but cannot find the solution. Could you point me where could I find it, please?

    Many, many thanks.

    1. Have you already attached a display unit (monitor)? Any picture on the screen?

    2. As far as I can see, all of the RAM ICs are socketed, right? Did you check them one by one?

    BTW ... dual spring-contact for the IC-sockets would be much more better than the one's on your board ... they are not reliable and are often causing contact problems.

    1. Yes. I even uploaded the video at Youtube and linked it in the thread in the first post, but I link it again here -> (

    2. Yes. Every U256 is socketed. In fact, I placed every socked on this board, even replaced the old ones -if the ICs were rusty, I couldn't expect the sockets to be better-.

    I was told just the contrary, that precision sockets were better. Does that mean that I must desolder every one of them and resolder again? :pinch:

    Thank you very much

    I have a scope, it's half-working but that should be enough. I'm using Zimmer's schematics for this board (he really did a good job gathering all that information).

    The 555 in the reset circuit has been replaced as was mostly eaten with rust. About the clock, my probe detected pulses at the output. But I guess I should check them. If they weren't the responsibles for the failure, wouldn't you know what should I look for?

    Thank you very much for your answer.


    I'v been a couple of days working my CBM 3032 repairs. I started with this junk board:

    And left it in this state:

    There are a couple sockets more, but the output does not change. I have configured the jumpers as the technical manual states and replaced every EPROM with its original BASIC 2 from Commodore (NOS).

    The 6502 has been tested and is working, her only PIA has been replaced (missing pins) and the second one has been added. Some components like the '154 or the 555 have also been replaced because they were prey of rust.

    After testing a few times the result is this one.

    I'm also having no DOUT at the U256:

    And CAS fixed at high-level.

    I've tested some ICs regarding CAS and seem to be working... so I don't know what could be the issue.

    About the video circuit I'm sure there is a failure too, because those "junk" values should fill the screen completely but they do only occupy 2 1/2 lines in the middle of the screen.

    I am not sure about what should check now. There's no expertise in any system of the PET/CBM line in Spain as their sales were poor (and that's being generous). There are only a few of them, most in universities or in hands of speculators, some of them being offered for no less than 800€ or even in the range of 2k-3k€. For this reason I thought this is the best place to come for some help with this system.

    Just some background... This unit is nicknamed "The International" not without a good reason. Its case, PSU and monitor came from UK in a single block. Its BASIC 2, Kernal and Editor ROMs came from the same source. The keyboard came from Germany in a three units pack (all of them incomplete but I was able to build a working and complete one from pieces from the two 2001N, the other was one from a B model). The PIAs came from the UK too, but from a different source. After three years we found its board, which came from Italy but had memories manufactured at DDR. The character ROM was from the only Andorran PET, which is working but has some strange video problems. In other words it came from all around Europe.



    Wait! Are you really talking about vinyls?

    Therefore I accuse you of the terrible crime of being modern. :P

    Computers aren't my only interest... I really collect nearly everything classified as old. Music is not an exception. I own approximately 300 shellac disks, most of them at 78rpm, others at 80; most are standard but Pathé records are also present even if I'm unable to read them. Also there are berliners and 3 metal disks (a couple of them still have a side free to record). My turntable is about 50 years old, is portable and employs vacuum tubes. Would you like to see them?

    Some contemporary music I listen in less exotic formats are basically soundtracks by Ennio Morricone, Hans Zimmer, Jerry Goldsmith, John Williams, Danny Elfman, Basil Poledouris, Fujisawa Mamoru (aka Joe Hisaishi), Sakamoto Ryuichi and Kawai Kenji among others.

    Today I went to La Seu d'Urgell. Unfortunately the flea market is almost gone.

    I have visited l'Escrit (that office that was once pictured here in this thread) and its owner was amazed when I told him that his business was known in Germany. He told me that his son found pictures of their machines in a Japanese website.

    Even if the flea market has mostly disappeared, I found a place where I got some interesting items.

    A couple of NES games

    Three complete PSX games and the manual of Metal Gear Solid.

    And a complete 3DS game.

    In another place I found a calculator that I was searching for some time. It was my grandfather's but was damaged by dogs before I could see it. I have been fortunate to get an exact match but it cannot replace what's lost.

    On the left my grandfather's calculator, on the right the one found today.

    It's funny to know that they are known outside... but did they really called them so in the Deutsch translation? :shock:

    Just for the record:

    "Filemón" is a Spanish name, nothing special about it; isn't the most popular either but now even less due to the character.

    "Mortadelo" is not a real name. Is a forced masculine of "mortadela". This word has no direct translation to English but according to Google translator it should be "Wurst" in yours. So it bears a name of something similar to a sausage because he is tall an thin.:)

    It's sad when one finds that translators made only half the work and took a shortcut instead...::cry::

    Today, at the same site where I found the MSX-Basic beta videotape tutorial (I was searching for the missing part) I got the following items:

    #1: Nintendo promo VHS "Alto Riesgo", 1996

    Unfortunately, seems broken. Maybe with a donor VHS tape I could fix it.

    #2: Hard disk drive

    3 1/2" hard drive. The acquisition is so fresh that I still haven't got time to check its capacity, so I don't know how many megabytes it could store. Not very slim... very fat indeed.

    #3: Tebeo #126

    Tebeo was a Spanish comic magaziine, very popular during the 80s. It usually contained the stories those of the secret agents "Mortadelo" and "Filemón" and some other characters from other cartoonists. That magazine was so influential among the then young readers that comics are informally called "tebeos" in Spain. But the reason I took it was the last page of it.

    I found strange for a Spanish magazine about Spanish comics to came with publicity from a Japanese comic. Comics from Tebeo are very lighthearted while Akira is dark. Being 1989 in Spain I could have expected Doraemon or Dragon Ball being announced, but not a pivotal genre-defining Japanese cyberpunk work. So I found it curious and brought it home.

    After 3 months in transit and a complaint later my memories have arrived this same morning. They were expected to arrive a month and a half ago.

    I think that it is not necessary to say that once I received them rushed its construction...

    Then proceeded to its testing.

    FFEF -> 48KB recognized!

    That being said, I introduced a small error in the design of the board: about 1-1.5mm should be removed in order to place the bus connector. Otherwise everything is fine.


    I found a Betamax tape.

    If really contains what the sticker says, it should be a MSX Basic videotutorial. Case and a second tape are missing; cannot test it because I don't own a beta player. However I guess this is better than nothing.

    It is a subjective matter.:nixwiss:

    In my case, my line for the PC is drawn at Pentium II (cpu <= Pentium II ? retro : just obsolete).

    However, it's up to you where you decide to draw the red line. I must admit that I haven't seen any computer from 20 years ago like this one you show. Any Pentium III I've seen came in a bulky metal cream-colored case. Sadly most PCs from then on seem all the same to me; if any unit is found its fate is just being scrapped for its PSU or expansion cards.

    I'd like to see in which side of the border you place it. Just curious.;)

    Konsolen-Neuzugänge und Atari Merchandise :-)

    Nice acquisitions! That GX... rare to find it boxed nowadays.

    If that's your first NEC TG-16, I recommend you to get an adapter to play PC-E HuCards (a large portion of titles for this system never left Japan). It is, however, nearly mandatory to acquire a CD-ROM2... Its best games are in that format. Do you have a NTSC TV or you'll mod it to output RGB?



    About two weeks ago I went to "Saló del Manga" in Barcelona and made some good findings. After my return I was very busy and that's why I didn't share this with you before...

    I got, as expected, Japanese content as books and movies. I got more, but only what I consider the most interesting of them are here:

    The golden age of the flying boat, by Miyazaki Hayao

    Movie theatre booklet of "Hotaru no haka", unopened since 1988

    Rupan sansei: Kariosutoro no shiro.

    This last one is very important. If, when young you played "Cliff Hanger", you actually watched fragments of this movie. It contains the prototype characters of some of Miyazaki's movies (it was his debut as director) such as Nausicaä, Fío, Muska, the Men in Black, Curtiss and apparently was used by the development teams of Konami during development of the original (pre Lords of Shadow) Castlevania/Akumajou dorakyura series.

    In the purely retro side, I found some interesting items from the three regions...

    Super Game Boy, the only European piece that I was able to acquire.

    This one was a surprise... It came apparently from the USA.

    Everything else came from Japan.

    Dorakyura Densetsu II

    Ghost in the Shell

    Ni no kuni

    This last one is very special because animation was done by Studio Ghibli ("Sen to Chihiro no kamikakushi", "Hotaru no haka", "Kurenai no buta", etc.). The composer is Joe Hisaishi, who has worked with Miyazaki since 1984. Being an special edition the box also contained a book which is the game's guide.


    The power supply is now feed through a custom connector from the backplane.

    After some checks it worked as expected. However, some seconds after mechanization of the custom connector, my dremmel-like tool started with an awful performance and then generated white smoke. I guess it is an ex-tool now.

    That's all for now. :):thumbup:


    I never experienced any of those issues. In my case, I just plugged the ATX PSU into the P2 or P3 backplane (with the simple adapter that I uploaded here already) and everything worked fine. In my P2 I connect the floppy drives directly to the floppy power connectors of the ATX PSU. In the P3 I keep the backplane wiring, i.e. the floppy power is provided via the original power cables leaving the backplane on the left side. Both approaches work flawlessly. I also never discharged anything and was not hit by electrical shock so far in the computers.

    I had to replace the connectors as I used an ATX 2.03 (P4). Every not used wire has been desoldered. Green has been curt short and soldered internally to GND so it awakens as soon it is connected to the power grid.

    While testing the adapter I had some trouble. R3 (labelled as a 390 ohm) is too small; killed the LED (D3). I replaced it with a 1k5 ohm resistor, also used in R2.

    I realized that the shutdown is indeed the short circuit protection system. So, something in my adapter is wrong and causes causes short circuit when connected to the backplane.

    I also found a way to discharge the PSU. I'll check if having grounded "green" is enough, otherwise it would need to be done manually.

    EDIT (3:08AM)

    Found the cause of the failure. Silly me. :wand:

    It's working now but will need the rearrangement of some parts. I will also mod the PSU again to legthen its inputs enough to pass them through the same overture as the outputs and feed itself from the backplane.

    Tomorrow, more tests.

    Regards and good luck!


    This afternoon I have modified my ATX to adapt it to overCLK 's board. I've built one of the boards too.

    When powered, without being connected to any backplane, it behaves as expected as all LEDs turn on. However when connected to the P3's one the LEDs flash, a short buzz is heard from the PSU and everything turns off. Being a PSU test it has no boards connected to prevent any possible damage. I guess that I've chosen wrong the +12v lines... I recall now that the floppy disk +12v lines must be isolated. Could this be the cause? I also need to discharge it to prevent shock... ATX use to be active for a long time after disconnection. Prior to the mod it was not powered for months (just for in case). Do you know a fast and secure way to do it?

    Thank you very much,


    There are guys in France which are programming graphical demos on Minitel. So it is not as useless as someone can think about.

    I asked on another forum for ideas, and someone came ta say that I coud use it as a terminal for a KIM. I don't have a KIM, but an AIM. Having some sort of screen for that computer sounds great.