Re: faulty IEC serial port on Flat NTSC C-128

Hi Rudd,

 Well theres the TTL Logic Bus Transeiver chip.  I pulled a lot of pads and
3 traces.
I looked very carefully and so repaired the pulled pads and traces I just
need to test it now when
I get to it.

Im finding my desoldering skills are horrible.

Terry


On Mon, Nov 1, 2021 at 7:00 PM Roberto Muscedere <rmusced_at_uwindsor.ca>
wrote:

> If it works in 64 mode, then my guess it is the fast serial shift register
> circuits. The MMU drives the FSDIR signal which sets up the direction of
> the shift register. You are looking at U8, U37, U16, U30, U58, U60, etc.
>
> You could also maybe test this by removing pin 1 from the serial
> connection which effectively makes the drive slow serial like the way the
> 64 mode would see it.
>
>
>
> Roberto
>
>
>
> *From:* Terry Raymond [mailto:traymond160_at_gmail.com]
> *Sent:* Monday, November 01, 2021 1:35 PM
> *To:* cbm-hackers_at_musoftware.de
> *Subject:* faulty IEC serial port on Flat NTSC C-128
>
>
>
> Hi all,
>
>
>
> I have a USA NTSC Flat C-128  STOCK:
>
> This 128 powers up just fine, and it resets in all modes.
>
> The problem is that all of my disk drives wont work with it,
>
> it just pops up this error message:  DEVICE NOT FOUND ERROR?
>
>
>
> I have run the C128 Diagnostic with the harness attached and it really
> doesnt mention the
>
> IEC serial port as not working etc.
>
>
>
> The CIA chip for the IEC circuit tests okay
>
> I replaced the TTL Logic Transeiver Bus chip, socketed it.
>
> I replaced all of the IEC circuit I believe switching Diodes?
>
> I replaced the IEC Din serial socket.
>
>
>
> With all of that I still get the error message.
>
> All I can figure is maybe i pulled pads or traces on the TTL Logic
> Transiever chip.
>
>
>
>   I just did purchase a good Oscilloscope and getting a crash course on
> how to look for
>
> high/low stuck bits etc and how to trace down a bad IC.
>
>
>
> Other than that has anybody else ever had this failure?
>
>
>
> BTW in the Diagnostic though the User port tested bad) since the
> Diagnostic uses that cartridge in the user port.  So I cleaned the Edge
> connectors and then it passed.
>
>
>
> BTW I do have the C-128 Dead test and Diagnostic.
>
> and I do have 2 different types of the harnesses, I cant recall the person
> that made them, well one was made last year in Canada.
>
>
>
> Terry Raymond
>
>
>
>
>
>
>