Falcon doesn't initialize blank screen

[sdisla]

Question for you, a bad VIDEL chip can cause the system to halt? I thought that is just not video but at least able to initialize.

The Videl chip also controls the RAM.

The diagnostic cartridge only needs the system to be somewhat alive, mostly CPU being able to run with ROM.

Exxos,

The floppy drive does not light or flicker dimly at all.
So, in this case I guess is to keep looking for anything related to solder joins.
Also, I check the 5 volts on the RAM which are there.
Anything else I can check on the VIDEL chip to ensure that is not working properly?
I check pins 14,44 & 73 ext clk is there also 25 & 32 MhZ

Thank you,

Floppy LED.jpg

[Badwolf]

Thank you for your feedback. As per your instructions I check pins 51,52,53,54,55,56 getting the same result on each of them.

Those are address line pins. I'm not sure which ones you're showing us, but it does look like some activity at least.

AS is address strobe and is a different pin entirely, but I don't think it's needed any more in this case as you've just proved connectivity.

The expansion port is a good place to probe these things, by the way (you'll find the pinout online -- start with dev-docs.org).

Anyway, it's difficult to read but it looks like there's about 2us between pulses on the lower address lines there. By my reckoning that should be only about 500ns, so that feels wrong.

Next step would be to try to probe the ROM's CE line (chip enable). You'll need to consult the schematic from dev-docs and find the appropriate pin on the PLCC socket under the memory board.

In that case just leave the memory board out whilst you probe for CE after reset. You ought to have a decent number of quick-fire activations before things go south trying to use missing memroy.

Also: if your screen looks the same with the memory board totally removed, a dodgy RAM board connection increases in likelihood, IMO.

BW

[sdisla]

Thank you for your feedback. As per your instructions I check pins 51,52,53,54,55,56 getting the same result on each of them.

Those are address line pins. I'm not sure which ones you're showing us, but it does look like some activity at least.

AS is address strobe and is a different pin entirely, but I don't think it's needed any more in this case as you've just proved connectivity.

The expansion port is a good place to probe these things, by the way (you'll find the pinout online -- start with dev-docs.org).

Anyway, it's difficult to read but it looks like there's about 2us between pulses on the lower address lines there. By my reckoning that should be only about 500ns, so that feels wrong.

Next step would be to try to probe the ROM's CE line (chip enable). You'll need to consult the schematic from dev-docs and find the appropriate pin on the PLCC socket under the memory board.

In that case just leave the memory board out whilst you probe for CE after reset. You ought to have a decent number of quick-fire activations before things go south trying to use missing memory.

Also: if your screen looks the same with the memory board totally removed, a dodgy RAM board connection increases in likelihood, IMO.

BW

BW,

The signals from the scope are A4,A5,A6,A7,A8,A9

I will check for the ROM's CE line (chip enable) later today.
Also, if I remember correctly removing the RAM the screen is always black.
I can see the format 4:3 square super imposing the 16:9 on the monitor.
When the reset button is press and release it disappear for one second then it comes back but no green dots like when the RAM is present.

Thank you for the info.

AS.JPG

[sdisla]

BW,

Found PIN3 to be the ROM's CE line (chip enable) and there are some activities as soon as the power is up.

While the unit is ON if the reset button is press there are no activity as previously seen when the machine is turn ON.

On the other hand, the screen is just black once the Falcon is ON with the memory board totally removed.

Thank you,

CE.jpg

CE PIN3 ROM.jpg

4096 ROM.JPG

[Badwolf]

This is good. It shows your CPU is running.

My next suggestion would be to replace the memory board again, then probe the cartridge port for its ROM select lines.

The reason being if ROM code is being executed, shortly afterwards it will check for the cartridge being present. This will activate the ROM4 (or maybe ROM3 -- I can't remmeber, probe both) line that goes to the cartridge port.

carthead.png

You may find it easier to plug in the diag cart and probe the pins on the cart.

They're the fourth and fifth pins from the front of the machine, conveniently on the top side.

Bear in mind those cartridge pins are decades old and probably filthy. You may need to do a bit of cleaning of the cartridge port, the edge connector on the cartridge itself and anything else associated with it!

BW

[sdisla]

This is good. It shows your CPU is running.

My next suggestion would be to replace the memory board again, then probe the cartridge port for its ROM select lines.

The reason being if ROM code is being executed, shortly afterwards it will check for the cartridge being present. This will activate the ROM4 (or maybe ROM3 -- I can't remember, probe both) line that goes to the cartridge port.

You may find it easier to plug in the diag cart and probe the pins on the cart.

They're the fourth and fifth pins from the front of the machine, conveniently on the top side.

Bear in mind those cartridge pins are decades old and probably filthy. You may need to do a bit of cleaning of the cartridge port, the edge connector on the cartridge itself and anything else associated with it!

BW

BW,

I ordered a new 72 pin 60ns SIMM RAM to try your new suggestion.
On the meanwhile, I did a good cleaning on the existing one I got from EXXOS with the ST_RAM SIMM adapter.
Also, double check the traces on the bottom side of the motherboard and cleaned the old solder flux.
I will try the board later today.

Keep you guys posted.

SIMM PINS BOTTON MM.jpg

SIMM REAR.jpg

SIMM FRONT.jpg

ST RAM SIMM ADAPTER.jpg

[Badwolf]

The reason being if ROM code is being executed, shortly afterwards it will check for the cartridge being present. This will activate the ROM4 (or maybe ROM3 -- I can't remmeber, probe both) line that goes to the cartridge port.

BW,

I ordered a new SIMM to try your new suggestion.

I wasn't talking about SIMMs, I was talking about the cartridge port & the diagnostic cart you have.

BW

[sdisla]

BW,

I ordered a new SIMM to try your new suggestion.

I wasn't talking about SIMMs, I was talking about the cartridge port & the diagnostic cart you have.

BW

I got your instructions clear, you suggested to replace the RAM *Memory Board*
If it works the ROM code being executed will check for the cartridge being present activating the ROM4 or ROM3 then I will probe the two test points on the cartridge port and use the Diag-Cart to access these two pins easily.

While I’m waiting for a new RAM *Memory Board*, I will clean the one I recently got from EXXOS to see if it works.

I just did but still on the same failure mode after re-sitting the RAM *Memory Board* and cleaning the SIMM pins.

I guess at this point it's just mater to wait for the new RAM and try your suggestion.

[sdisla]

I wasn't talking about SIMMs, I was talking about the cartridge port & the diagnostic cart you have.

BW

I got your instructions clear, you suggested to replace the RAM *Memory Board*
If it works the ROM code being executed will check for the cartridge being present activating the ROM4 or ROM3 then I will probe the two test points on the cartridge port and use the Diag-Cart to access these two pins easily.

While I’m waiting for a new RAM *Memory Board*, I will clean the one I recently got from EXXOS to see if it works.

I just did but still on the same failure mode after re-sitting the RAM *Memory Board* and cleaning the SIMM pins.

I guess at this point it's just mater to wait for the new RAM and try your suggestion.

BW,
Anything else I can check while I get the new RAM card?
Thank You,

[Badwolf]

I got your instructions clear, you suggested to replace the RAM *Memory Board*
If it works the ROM code being executed will check for the cartridge being present activating the ROM4 or ROM3 then I will probe the two test points on the cartridge port and use the Diag-Cart to access these two pins easily.

I meant replace as in "put it back" in the machine. The RAM board was removed whilst you tested the ROM2 CE line.

I suggested refitting the RAM board and then testing the ROM4 line (and ROM3 whilst we're at it) on the cartridge connector.

We've shown the CPU is working. We've shown ROM is being selected. Does the cartridge start to be selected too?

If all three happen, we're halfway to getting the diagnostic cart working.

BW