[TenTec] Corsair II UV EPROM failure

A R raf_3 at msn.com
Sat Feb 15 22:33:01 EST 2014


Of course you're right, the UV is used only to erase the resident/existing program on a UV PROM. I knew that, and what I intended to convey to Clayton was that the PROM portion of the MC68705P3S is UV Erasable (not programmable), rather than Electrically Erasable. 
Replacing the term "programmable" with "PROM" in my original post reading " UV programmable, rather that EE programmable", would have accomplished my original intent, and accurately discriminated between the two subject methods used to erase PROM programs for the purpose of establishing fixturization required to "clean" PROMs before programming.

I like your "cheaper and easier" option. Volunteers?


 ----- Original Message ----- 
  From: geoffrey mendelson<mailto:geoffreymendelson at gmail.com> 
  To: Discussion of Ten-Tec Equipment<mailto:tentec at contesting.com> 
  Sent: Saturday, February 15, 2014 12:03 AM
  Subject: Re: [TenTec] Corsair II UV EPROM failure

  On 2/15/2014 3:12 AM, A R wrote:
  > Oh, man! Clayton, you're my hero. The prom is a 28-pin, and is UV programmable, rather that EE programmable. I believe the programming of my prom is good. It's just an input gate that's stuck low. If that's not a problem for downloading (if input gate states are not needed), then my prom should be good for acquiring the program.

  The UV applies to the E not the PROM part of the name. To be exact, the 
  chip is a microprocessor with a UV erasable PROM attached. To erase the 
  contents of the PROM in the package, you expose it to high intensity UV 

  Programming the chip is unfortunately far more complex.

  First you program a 2764 EPROM (also UV erased, but not relevant to 
  programming the microprocessor) with the desired data. 2764 chips are 
  relatively easy to find, you can get all you want used, erased, and 
  tested for under $2 each on eBay including postage. They are programmed 
  with the under $50 programmers you see on eBay. Although if I had to do 
  it again, I would spend $150 on a USB connected Wilem programmer with 
  the complete kit of device adapters, but I digress.

  The hard part is transferring data from the 2764 chip to the 
  microprocessor. That is accomplished with a special programming device 
  that boots up the microprocessor, and sets the program bit on. The 
  microprocessor boot code senses this bit, and reads data from the 
  attached 2764 and copies it to the chip.

  If you try to program the microprocessor without a 2764, it will program 
  it with worthless (I think all FF) data, you have to erase it (with the 
  UV light) and start over.

  The second link to a programmer is actually to a device that copies the 
  EPROM part of the chip to SDRAM and rewrites it to a fresh chip, There 
  are ways mentioned, but not detailed, to copy that data to a PC, so you 
  can program more than one, or archive it for later use.

    Here are some useful links:



  And while you are at it, a UV eraser sells for under $20 on eBay.

  Basically if you are handy with a soldering iron, have some computer 
  savvy, and want to do something new, you can get the whole setup for 
  around $100. Obviously it would be cheaper and easier to find someone 
  who knows what they are doing already, and has all the equipment.


  Geoffrey S. Mendelson 4X1GM/N3OWJ
  Jerusalem Israel.

  TenTec mailing list
  TenTec at contesting.com<mailto:TenTec at contesting.com>

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