Re: SSC Failure - odd symptoms

[BLuRry <brendan.robert@gmail.com>]

On Aug 20, 10:46 pm, Zero dB <n...@email.com> wrote:
> On Thu, 20 Aug 2009 18:29:51 -0700, Zero dB <n...@email.com> wrote:
> >On Thu, 20 Aug 2009 19:51:32 +0200, Patrick Schaefer
> ><pa.schae...@web.de> wrote:
>
> >>Zero dB schrieb:
>
> >>> It it possible for the SSC to fail in such a way that transfers won't
> >>> work, but the logic still does ?  I can "session" into the card and
> >>> get a responsive prompt, but can't transfer.
>
> >>Sure. The 6551 may have failed, or the baud rate generation circuit. If
> >>you dropped the card, the crystal may have broken.
>
> >>You can remove the 6551 from its socket and connect pin 10 to 12 with a
> >>jumper wire. Then start Hyperterminal on the other side and see if you
> >>get back what you're typing. If you see the remote echo, everything up
> >>to the UART chip is ok.
>
> >>Testing the crystal requires an oscilloscope. However, for a quick test
> >>you can just connect a working part in parallel. Usually a broken
> >>crystal is broken in a way that it isn't present in the circuit at all
> >>anymore.
>
> >>Patrick
>
> >Thanks to everyone for all of your help.  I really appreciate your
> >time.
>
> >I definitely am going to have to try to re-seat everything. I
> >attempted to be careful with the connectors cleanliness, and also
> >didn't use terribly high pressure, so everything is as-was, to my eye
> >anyway. Obviously something isn't as-was.
>
> >Moments ago, I did just pop the 6551 out and jumped tx/rx (10/12) as
> >recommended by Patrick. I got as far as "IN#2" at which point it just
> >started spitting out paragraph sized blocks of solid cursors followed
> >by a back slash, then another paragraph sized set of blocks, ad
> >nauseum.   No chance to attempt anything past that.
>
> >I'm certain it was in 10 & 12 with proper continuity, i checked the
> >dip pinouts on the schematic. tx & rx.
>
> >Re-apply the 6551 and all is well logically, but still no transfers.
>
> >Sure sounds like a user error, doesn't it ?  So weird, I have been
> >working with rs232 quite awhile and am certain that is all ok.
>
> >I will set forth with the reset/re-seat operation next........
>
> >any ideas on why tx-to-rx would cause such a fuss, patrick ?
> >again, it sounds like operator error but i triple checked the proper
> >pins 10 and 12. Simple enough, just 10 and 12 over from the dot
> >signifying pin 1.
>
> >Hrmmmmmmm.
>
> >Taking a break, will try reassembly later. getting anxious and
> >frustrated.
>
> >Jayson
>
> CORRECTION:
>
> I set up the loopback in the 6551 dip and connected a remote term
> (kermit) to the apple.
>
> It did echo my characters with local echo off, so it definitely made
> the round trip through the card.
>
> I will confess, i handled everything without a static strap, (just
> rushing and being careless), so during my process of disassembly and
> reassembly I must have blown the 6551 asic.
>
> I don't have any extras, time to start looking for a new SSC i guess
>
> Thank you for the T/S tip!
>
> Jayson
>
> jayson dot removethis anderson at gmail

Or you fried the onboard firmware PROM.  The ASIC may very well be the
only thing working on it.

-B