White screen with STacy

[exxos]

So all address pins are now high now all chips removed and wasn't before ?

[Roberto]

So all address pins are now high now all chips removed and wasn't before ?

Exactly, the address pins have gone high since I removed the MMU, SHADOW, C103663-001 RTC #1679 and the SHIFTER. I don't know which one actually caused this, because I did it by removing all of them together. It must be said that if I put all the chips back in their sockets (all I mean ROMs and all), the CPU pin addresses are all high.

[exxos]

Exactly, the address pins have gone high since I removed the MMU, SHADOW, C103663-001 RTC #1679 and the SHIFTER. I don't know which one actually caused this, because I did it by removing all of them together. It must be said that if I put all the chips back in their sockets (all I mean ROMs and all), the CPU pin addresses are all high.

Just to clarify that you actually just put the chips back and address lines are all high ? If that's the case then something has changed from earlier ...

[Roberto]

Just to clarify that you actually just put the chips back and address lines are all high ? If that's the case then something has changed from earlier ...

Actually I still have to put all the chips back in; mine was just a logical thought whereby before removing ALL the chips I remembered that the address lines were high. The address lines became low (or rather, exactly + 300mV), when I removed the ROMs, DMA and GLUE, and then went back high by removing also MMU, SHADOW, C103663-001 RTC # 1679 and SHIFTER.

[exxos]

OK.. So put back shifter and MMU. Holding down reset should make all address pins high... Then when you let reset out, all CPU pins should be low on the first cycle when reset goes high..

[exxos]

Also did you countinuety check all ROM pins back to the CPU ? Do with ROM chips in place..

[Roberto]

OK.. So put back shifter and MMU. Holding down reset should make all address pins high... Then when you let reset out, all CPU pins should be low on the first cycle when reset goes high..

I put the shifter and the mmu again (the shadow, glue, dma and the two Roms remain out), this is what I see: at power on all the addresses are low (about 200 mV), the / HALT signal when goes high, the addresses remain at the same level (about 200 mV); even if I press the RESET key nothing happens, no changes on the addresses (they remain at about 200V). however I noticed that if I keep the machine on for at least a minute, measuring between the various addresses I see this:

0097C894-DDAF-4759-92E1-594DEA153EDB.jpeg (210.01 KiB) Viewed 1444 times

then if I press reset the address lines go high. by pressing reset several times, the address lines return to low. it is not said that if I wait that minute I always get this screen, it may be that it never appears. let's say that this screen is easier to obtain by turning it on with the ON button.

[exxos]

I think you may have two different problems at least going on there.

But can you put minimum and maximum voltage markers on your scope screen ? It says PKPK which is peek to peek. There is no way to visually confirm what the voltages are varying between. Normally waveforms like that are bad PSU and vary between 4-5V.

[Roberto]

Also did you countinuety check all ROM pins back to the CPU ? Do with ROM chips in place..

this afternoon I check with the tester (with the machine off), the continuity of the ROM lines towards the CPU.

[Badwolf]

I think you may have two different problems at least going on there.

But can you put minimum and maximum voltage markers on your scope screen ? It says PKPK which is peek to peek. There is no way to visually confirm what the voltages are varying between. Normally waveforms like that are bad PSU and vary between 4-5V.

+1 for additional PSU woe, especially with a time (=heat) dependence.

BW