White screen with STacy

[PhilC]

@Roberto looks to me like your CPU is working. The 200ms range on your scope is too slow to look at address and data line, try something like 80us

[rubber_jonnie]

@Roberto looks to me like your CPU is working. The 200ms range on your scope is too slow to look at address and data line, try something like 80us

I'd agree, the timebase looks suspect, a tweak will make a big difference and may help you see what's happening on the address and data buses.

Also, be sure that you have have the switch on the oscilloscope probe set correctly, if its set to 10x you can hide signals.

[Roberto]

@Roberto looks to me like your CPU is working. The 200ms range on your scope is too slow to look at address and data line, try something like 80us

@rubber_jonnie @PhilC

I checked the probe, and saw that the measurements were always made with X1. I tried to use 80us but it seems that even with this setting it is not effective for displaying the signals correctly (you see a very close beam of signals) so I set it to 1us and these are the results for pins D0 to D4 , the rest (from D5 to D15 and all address pins are between + 1v and + 5v fixed). naturally with these oscilloscope settings I performed a test in real time (so not with Single SEQ).

25A89C57-3A81-4BE9-8356-218BEC51E963.jpeg (563.53 KiB) Viewed 1507 times

[exxos]

Doesn't look right... Switching constantly at only 1.8v on a data line.. Does it do the same with the ROMs removed ? In fact if you remove GLUE are they all 5v then ?

[PhilC]

Doesn't look right... Switching constantly at only 1.8v on a data line.. Does it do the same with the ROMs removed ? In fact if you remove GLUE are they all 5v then ?

I'm thinking his roms or their sockets are duff @exxos.

[Roberto]

Doesn't look right... Switching constantly at only 1.8v on a data line.. Does it do the same with the ROMs removed ? In fact if you remove GLUE are they all 5v then ?

now I have removed (in addition to the DMA) also the two ROMs and in addition, compared to before, I have the registers from D5 to D15 that pulsate as in the last photo I published. so I also removed the Glue chip and I have all the address pins at + 300mV and the data pins at + 5V.

[exxos]

Doesn't look right... Switching constantly at only 1.8v on a data line.. Does it do the same with the ROMs removed ? In fact if you remove GLUE are they all 5v then ?

now I have removed (in addition to the DMA) also the two ROMs and in addition, compared to before, I have the registers from D5 to D15 that pulsate as in the last photo I published. so I also removed the Glue chip and I have all the address pins at + 300mV and the data pins at + 5V.

Do all the address lines go high if you hold in reset button ?

[Roberto]

Do all the address lines go high if you hold in reset button ?

nothing is happening. for all addresses, by pressing (and holding down) the reset button, they remain like this.

B68F9A92-1DEF-4959-88E2-63DB010FB196.jpeg (185.39 KiB) Viewed 1488 times

[exxos]

nothing is happening. for all addresses, by pressing (and holding down) the reset button, they remain like this.

They should all be high. I can only assume at this point the CPU is duff. You could remove all chips in sockets just to make sure nothing else is shorting the bus.

Do the LS224 LS373 Chips get hot or look blown ?

[Roberto]

They should all be high. I can only assume at this point the CPU is duff. You could remove all chips in sockets just to make sure nothing else is shorting the bus.

Do the LS224 LS373 Chips get hot or look blown ?

I have two MC74HCT373AN which look perfect and don't heat up; in truth, no component heats up, even if they leave the power supply switched on for some time. I have not found the LS224; i have two MC74HCT244AN and one MC74F244N, and they also look perfect. I removed everything that is possible without using the soldering iron, therefore: the two ROMs, GLUE, MMU, SHADOW, C103663-001 RTC # 1679 and the SHIFTER. below, therefore, I measured a few pins of the CPU; clock absent (signal of 3v fixed), all data pins from 1v to 5v fixed, all pins fixed addresses at + 5v and no change by pressing reset. I have ascertained that reset and halt are at 5v (they are and they go low when I press the reset button).