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shoestring

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Posts posted by shoestring

  2. Posted · Edited by shoestring

     

    Yes, the MT-4067 are the same like 4464 or 41464. When you changed them already and system won´t start, the suggestion of using a wrong power supply by former user(s) is the most possible reason. I´ve had a lot of dead XL/XE on my desk which were try to power-up with a Commodore C64 power supply... instant dead will follow. :-o

     

    The 40 pin IC down below the DRAMs is the Freddie. Freddie ist just a simple ASIC which containts some DRAM access logic and clock divider. In most cases the Freddie is also blown out when using wrong power supplies like the C64 one (this one has 9V AC... ). The reason here is, that Freddie is manufactured in CMOS, all the other custom chips from Atari are manufactured in NMOS. Most times all NMOS chips survice such a "Commodore attack", but DRAMs (also most CMOS in the XE series with two 41464) and Freddie are dead.

     

    If you own an oscilloscope, check the following points...

     

    - Pin 7 of the CPU (SYNC). Should be some transitions visible after RESET. Maybe flat line at 0V after some cycles (CPU hung up). If absolutely NO activity after RESET / Power-Up, no PHI0 clock is provided to CPU

    - Check OSC output of Freddie (Pin 37). This is the "master clock" for ANTIC, this one will generate PHI0 for CPU. OSC should be around 3,5xx MHz. If no transistions visible, Freddie is dead

    - Check pin 33 (RAS) and 35 (CAS). RAS must be constantly active, CAS also. Also no transistions = Freddie dead

     

    Without oscilloscope my Sys-Check might be helpful, but of course not in all situations.

     

    Good luck, Jurgen

     

    ' Commodore attack" :D . I suspect a power supply was responsible for this.

     

    A work colleague of mine picked up this 65xe and an 800xl off eBay. He described a buzzing sound and rolling picture ( sound familiar ?? ).I ended up repairing the 800xl which also had a single DRAM fault at U9, I replaced the whole stack of 8 with m3764s. The machines came with 3 power supplies, one of them was C70042-1 'The Logo' and the other two were identical but I had never seen those types before. All encased in epoxy and non repairable. Some vandal had also been poking around inside the 65xe and destroyed the variable resistor at R38, I suspect this is for the colour adjustment.

     

    After testing the 800xl & repairing it, I salvaged the leads+7 pin din connectors for a switching adapter solution and tossed the power supplies in the bin. I was rewarded with the 65xe for help with the 800xl, so now it's mine to fix. I have a really nice Tektronix TDS3054 scope to get the job done.

     

    Thanks for the troubleshooting points, I'll post some results once I make more progress.

    • Like 3

  3. Posted · Edited by shoestring

    They're just standard 4 bit 64k DRams. The MT brand are notorious as being unreliable to the point of some people replacing them even if they work OK.

     

    Good practice is to put sockets in before the replacement chips. And use a known good power supply, there are some variants that will go overvolt when they get old and kill systems. Unwanted buzzing in the audio can be a symptom of a PS that's bad.

     

    To get 128K you'd also need an EMMU chip which goes into that lone socket below/right of the Ram sockets. Not sure if that's the complete requirement, might be a few passive components needed as well.

     

    The MT DRAMs were so far gone that my EPROM programmer ( Micromaster LV48 ) couldn't recognize them and was prompting to check device and position ( as though no device was installled in it ). Normally it will either pass tests or fail when it reads back the wrong value at a given address.

     

    I put some sockets in this already and installed some TI branded DRAMs.

     

    I'm more interested in upgrading it to 512kb which requires an SRAM package, it's requires more work but is more worth while than the 128kb mod.

  5. Posted

     

    Hi all.

     

    I have picked up a dead and battered 65xe that produces nothing but a black screen.

     

    It has what appears to be 2 x 64Kx4bit DRAMs ( MT 4067-12 ). Are these just 4464s? The data sheet seems to confirm the same pinout. I'm still getting nothing after replacing them with known working DRAMs which are a little faster. FYI I'm using a known working power supply which I use for my other Atari's.

     

    I tested the MT-4067 DRAMs out of circuit and they seem completely dead so I'm suspecting that a faulty power supply took these out and perhaps other circuitry as well. The 40 pin chip at the bottom left is stone cold compared to the other chips which run warm, looking at the circuit it appears that this chip is some kind of DRAM address decoder??

     

    I'm just looking for some advice on probably causes before I start doing some troubleshooting of my own as I have no experience with the XE series and I'd like to get the memory in this upgraded eventually and the exterior cleaned up :)

     

    Thanks in advance.

     

    Some pics of the machine and my current progress.

     

    f4323f72c4bf17509f8b39029c838202.jpg

     

    0d0bba061e81754ae8b51d4fc173f347.jpg

     

    523337d4065e251082367e6c3044262f.jpg

  6. Posted

    These are decoupling capacitors, their main purpose is to filter out high frequency noise.

     

    The signal diode looking things are capacitors too, I've seen them mixed up with other types in the dram circuit . I guess they use everything they get their hands on and leave nothing to waste :)

  12. Posted · Edited by shoestring

    My Amiga 500 got me into some trouble.

     

    I used to call BBSs for free Australia wide via a poorly setup diverter ( it would forward calls if you dialled quick enough ). I had a script which dialled up the diverter after hours and then quickly dialled the phone number of a BBS to get the free call.

     

    There were a number of us doing it and the phone company caught on. We all received threatening letters to stop abusing the diverter.

    • Like 2

  17. Posted

    It would work in an open case but I don't know if that would work in all cases. RAM fails in many different ways.

     

    Say for example say you have a stuck low bit on the output of the bad chip, piggybacking a good chip would still drive the output low? Or you would have the stuck low bit superimposed over the good output?

     

    Best to remove all those DRAMs, install sockets and test them individually.

    • Like 1

  19. Posted

    The Multicades are great. They provide the closest experience you'll get to an original PCB due to re-implementation of the hardware in FPGA form.

     

    What I don't like is emulation in those cheap/underpowered boards, the audio quality is atrocious.My biggest issue is with the bootleggers who don't have any rights to distribute the rom images and are using MAME code in their products. I really question their ethics and I would never give them my money.

  25. Posted

    I think sound quality was still below par considering what the above mentioned sound chips could do.

     

    Other software houses were taking full advantage of the SID and POKEYs capabilities so I was generally disappointed when I finally got the chance to play some Br0derbund titles on my C=64.

     

    The Apple always played, felt and sounded better. But my opinion may be somewhat biased as I originally played those games at school on a //e system.

    • Like 1
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