Hi from Manchester UK

[rubber_jonnie]

An RS232 loopback is an RS232 loopback really. It may or may not test the modem control lines as well so that wiring could possibly be different.

Looking at the connected pins I think mine may test the modem control lines, as I say it came with my full test harness so I believe it to be reasonably comprehensive, though I can't say for any other dongle.

[Vipersan]

A quick copy ...
Cup of coffee....then test
:D :D :D

[Vipersan]

dongle fitted in 25 pin modem port..
waited for the menu to catch up..
ran test S = serial.
55 IRQ ok ?
56 RS232 transmit error 68901
fail at cycle 000001

conclusive ?
could be faulty silicon U203 ...or maybe another chip...or possibly another open circuit trace ?

[stephen_usher]

There's not a lot between the MFP and the rest of the system so probably buzz out the data lines, address lines and /DTACK on the chip back to the CPU.

Untitled.jpg

[Vipersan]

Yes indeed..
I'll let you know if I find anything..
I tend to use this :-
Clearer...active search...and has proven to be very helpful so far.
file:///C:/Users/Vipersan/Downloads/kicad-conversions--atari-ste-motherboard--c300780-001--v1.0.0-2.pdf

a must have for aged failing eyes like mine.

[rubber_jonnie]

Have you run the timing test (T) from the cart to see if it behaves like it does at boot time?

[Vipersan]

Just did that Jonnie T =
Testing MFP,Glue timing Video
Green screen / Pass

Then a long wait time of about a minute before the menu returns and I can then run another test.

[rubber_jonnie]

Just did that Jonnie T =
Testing MFP,Glue timing Video
Green screen / Pass

Then a long wait time of about a minute before the menu returns and I can then run another test.

If you hit space after a test finishes it should go right back to the menu immediately.

Definitely a weird one.

[Vipersan]

Been doing some probing with the meter in continuity..
RXW Checked pin 1 U203 to various destinations..all check out ok
SERIAL TX Ckecked pin8 U203 to U206 pins 4 and 5 ...ok
SERIAL RX checked pin 9 to U207 pin 3 ..ok
VCC pin 11 U203 ..ok
now for my first oddity
Pins 7 , 10 , 16, All reference timer_d (U203)
Not checked the pcb underside as yet ...but probing these pins component side.. I would have expected them to be connected together ??
but they are not..
sure enough pin 7 U203 is connected to pin 10 ....but pin 16 is isolated ?
this merits further investigation imo...but my old eyes are tired so clocking off for today.
What say you Stephen or Jonnie ..
should all 3 pins be connected together...?
rgds 2 all

[rubber_jonnie]

Been doing some probing with the meter in continuity..
RXW Checked pin 1 U203 to various destinations..all check out ok
SERIAL TX Ckecked pin8 U203 to U206 pins 4 and 5 ...ok
SERIAL RX checked pin 9 to U207 pin 3 ..ok
VCC pin 11 U203 ..ok
now for my first oddity
Pins 7 , 10 , 16, All reference timer_d (U203)
Not checked the pcb underside as yet ...but probing these pins component side.. I would have expected them to be connected together ??
but they are not..
sure enough pin 7 U203 is connected to pin 10 ....but pin 16 is isolated ?
this merits further investigation imo...but my old eyes are tired so clocking off for today.
What say you Stephen or Jonnie ..
should all 3 pins be connected together...?
rgds 2 all

Not sure I'd have to look at the schematics, will have a look tomorrow.

My eyes are not so young any more either...