Re: SSC Failure - odd symptoms

[Zero dB <no@email.com>]

On Thu, 20 Aug 2009 18:29:51 -0700, Zero dB <no@email.com> wrote:

>On Thu, 20 Aug 2009 19:51:32 +0200, Patrick Schaefer
><pa.schaefer@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