Image Map Image Map
Results 1 to 8 of 8

Thread: TRS 80 Model 1 - Weird Memory Problem

  1. #1

    Default TRS 80 Model 1 - Weird Memory Problem

    Guys, in addition to the M1 which got the EPROM 2732 1.3 ROM upgrade last weekend, and which runs perfectly stable for hours now, I also have another M1 (with the nice Alps keyboard), and that one is giving me headace.

    This M1 had some bad memory which got replaced. Now, with new memory installed, it is "mostly" running, but occasionally, games such as "Defense Command" freeze or crash after a couple of minutes, and when I run a BASIC program, I find that the M1 randomly resets, or breaks. Sometimes, I find that the BASIC program got modified! Very weird.

    Now, I tried to run the M1 at an as low voltage as possible (4.8 V), because apparently I killed some RAM chips at 5.08 V before... it seems these old chips are very brittle. So I want to keep them "as cool as possible".

    Question - Can 4.8 V be too low voltage now, and can that "slight under-voltage" cause the described slight memory corruption effect? Or is it likely that the RAM is "just a little bit" defect? What other problems might cause the effect?

    I will also try replacing the slightly degraded keyboard connector cable with pin headers and such, that will probably also benefit the overall signal quality on the bus...

    Thanks for any input!

  2. #2

    Default

    Quote Originally Posted by LambdaMikel View Post
    Question - Can 4.8 V be too low voltage now, and can that "slight under-voltage" cause the described slight memory corruption effect?
    Yes.

    The difference in heat output from 4.8v isn't going to make any difference to whether the chip fails or not or how fast.

    What makes you think you "killed" some RAM chips at 5.08v?

  3. #3
    Join Date
    Mar 2013
    Location
    Chaffee, MO
    Posts
    1,381

    Default

    LambdaMikel,
    The +12.0 VDC Power Supply must be adjusted properly first. Then the +5.00 VDC Power Supply
    must be adjusted for +5.00 VDC. That low of a 5 VDC didn't harm the Power Supply. You need
    a good Memory Diagnostic to locate the bad RAM, assuming the Power Supplies are working correctly.

    BabyRoot would be a good choice for Memory Diagnostic.

    Do you have the "Radio Shack TRS-80 Micro Computer Technical Reference Handbook 2nd.pdf" Hardware
    Manuals?

    Send me PM with your email address.

    Larry

  4. #4

    Default

    Thanks both - yes, I have adjusted both 12 V and 5 V deliberately to the current values, and confirmed / measure with multimeter. I do have the Technical Reference Handbook.

    I am not sure what caused them to fail - during the process of fixing this M1, a couple of RAM chips failed... 4 so far. It worked for 10 minutes, then garbage on the screen. Then, the finger test confirmed - another one burned out. So I kept swapping the old ones with new ones, and lowering the voltage. Maybe the chips were just too old by now. I have ordered another new set of RAM chips... maybe mixing and matching them (2 different manufactures, old and new) is not a great thing to do.

    Just guessing here. Will increase the voltage to 4.9 or 5.0 V again and see if the mem. problem goes away. Hopefully, not more burn out - this is getting expensive

    Good to know that the 4.8 vs. 5.0 shouldn't make a difference in terms of longevity of the RAM chips.

  5. #5

    Default

    Quote Originally Posted by ldkraemer View Post
    LambdaMikel,
    The +12.0 VDC Power Supply must be adjusted properly first. Then the +5.00 VDC Power Supply
    must be adjusted for +5.00 VDC. That low of a 5 VDC didn't harm the Power Supply. You need
    a good Memory Diagnostic to locate the bad RAM, assuming the Power Supplies are working correctly.
    Larry
    Bear and Larry,

    I have cranked up the voltage to 4.95 V now, and so far the memory is stable.
    So it seems it was indeed too low, in an abundance of caution on my side...
    Problem solved. Thanks to both of you!

    Michael

  6. #6
    Join Date
    May 2013
    Location
    Williamstown Victoria Australia
    Posts
    415

    Default

    Hi Michael

    Welcome to the TRS-80 world.
    Well done.
    Ray
    If it ain't Broke then PLEASE DONT fix it.
    Procrastinators Unite.
    I keep telling you I am Not Pedantic.

  7. #7

    Default

    Quote Originally Posted by Audronic View Post
    Hi Michael
    Welcome to the TRS-80 world.
    Well done.
    Ray
    Thanks Ray! Your avatar sounds and looks familiar... good to find that we also have some CPC enthusiasts here!

    Yesterday, my Expansion Interface arrived - was sold as untested, but it works! It is the redesigned one (2nd PCB revision). Have 32 KBs by now, and played "Penetrator" for an hour, the only 32 KB CAS tape game file I could find (any other candidates?) - memory is stable.

    Unfortunately, USPS handled it roughly, so a piece of the (very brittle) plastic broke off. I can cover that somehow with some decal metal tape or sticker or the like. But still looking very good.

  8. #8
    Join Date
    May 2013
    Location
    Williamstown Victoria Australia
    Posts
    415

    Default

    Hi Michael

    Yes getting an expansion Interface makes it all worth wile.
    My Trs-80 stuff, M1,System-80 (Dick Smith) (Video genie) M3, M4, M4p, plus FREHD's and Lo-tech TRS-80 IDE Adapter rev.2's
    I came from the Trs-80 world to The CPC world as we had run out of projects ?
    Have a look at the "FREHD" Sd card hard drive equivalent.
    My Operating system was always " Newdos-80" , ("No reply will be entered into about Operating systems")
    Your input will be warranted for the TRS-80 world.

    Thanks. Ray
    If it ain't Broke then PLEASE DONT fix it.
    Procrastinators Unite.
    I keep telling you I am Not Pedantic.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •