Robson's H5 x 2

[Robson]

Two boards (one for me one for a friend).

50% success rate at the moment.

Board #1 goes HALT. Voltages, clocks are fine. Need more time spendin on this . Same chipset works on #2.

Board #2 had seems to be alive ok. Need to complete with all other ports but wanted to quickly see first after #1 problems if this will be ok.

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[exxos]

[Robson]

On #1 - A23 shorted to gnd. Nothing obvious to notice.

CPU, GLUE, (Blitter if) are using it as far as I know + 5V/3.3v ports. I''m not using the Blitter, socket not added. I have one 64pin socket fitted only (#4).

What 's the best approach to isolate the short? I don't want to make too much mess by cutting, etc.

[exxos]

This kinda thing is why I use a low resistance meter... I will see if I can put up where A23 goes.. might give you some clues..

EDIT:

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The only place I can even see GND near it is under the CPU...

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[Robson]

Great, thanks. Definitely helped me a lot with the pictures and the tip. I have a low res meter too and dug it out.
Located that the lowest value is the through hole at port #1, so carefully made a cut under the smd glue pin and another under Pin 52 of port #1, cutting that area out. Then linked pin52 of port#3 to the smd glue pin. Values are now ok.

It showed some sort of life briefly, however bombed out and diag cart picture also fell apart and started scrolling + going crazy.
Now back to white screen only but CPU is not halted anymore if no diag cart plugged in. With the diag plugged in it goes low. So still looks like some addressing/decoding problem.

more to come...

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[Robson]

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[olivier.jan]

Did you check if the resistor network (RN7) was soldered in the right direction? Some people, me included, had some SMDs soldered upside-down.

[exxos]

$FFFABA isn't even a valid address..

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Nothing should be accessing it, so have you done verify ROM ? Looks like you have PP's modified TOS104 so you really need to try a generic 104 so the diag cart can do a proper checksum on it.

[Robson]

Did you check if the resistor network (RN7) was soldered in the right direction? Some people, me included, had some SMDs soldered upside-down.

I have some soldered upside down. I don't think that's an issue here. They seem to be isolated resistors.

[DoG]

Do you only run with 1Mb or is the diag reporting it wrong?