27 Jan
2007
27 Jan
'07
8:49 a.m.
From: Don North <ak6dn at mindspring.com>
I've repaired three separate DZ11s in the last couple of years. All the
failures were in the 40pin UART chips.
cctech at porky.vax-11.org wrote:
>
>One of the RS232 chips DEC used would blow if it was powered up after what
>ever was connected to it. So, you had to turn the computer on before the
>monitor or vice-versa.
>
>Clint
>
>On Fri, 26 Jan 2007, Tony Duell wrote:
>
>>>
>>>>1) 90-odd% of DZ11 failures are defective RS232 driver/receiver chips,
>>>>probably damaged by spickes induced on the RS232 cabling
>>>
>>> If they fry so easily, why not change the RS232 driver for
>>>something
>>>like max 232?
>>
>>They don't fry that easily, my comment is that the rest of the logic on a
>>DZ11 card is even more reliable, so that most of the (few) failures you
>>get are of the line driver/reciever chips.
>>
>>Anyway, why do you think the MAX232 would be any more reliable?
>>
>>-tony
>>
>
Hi
Once bought a pile of modems from a surplus shop. I think I bought
about 10 of them. I suspect they were field returns. About 8 of them
had what looked like lightning damage. One was even missing some
smoked traces.
These were bus mount boards and as I recall most all of the UARTs
were functioning. As bus mount they had no 232 level converters
As I recall, I got 3 boards working out of the pile,
just using parts from others. I think I payed about 1USD each for them.
They were all 2400 baud but these were at the time when the
newer high speed modems were still out of my price range.
Dwight
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