Falcon doesn't initialize blank screen

[sdisla]

Hello everyone,

I recently acquired a Falcon 030 that was in a storage for a couple years. Unfortunately, when I powered up it did not initialize correctly, giving me a black screen with a few green dots, see pictures attached. Found that the 12v line on the power supply was missing. Instead of re-cap the power supply, I got a new one. Unfortunately, the problem persisted so after reading some similar issues in the forum I did the mandatory upgrades. 

I changed the NVRAM module, clock patch, cap C147. After these upgrades the issue still there, blank screen (black with some green dots) power LED is ON, floppy LED is always OFF. Taking it further, I checked for voltages on all ICs, signal clock, oscillator and shorts and no issues. Lastly, changed the ROM and RAM but still in the same failure stage. After checking deeper COMBEL IC was only providing 8MHZ to the CPU, check RESET, HALT & BERR signals to pins 64,129 & 130 - all high with 5volts present. While pressing the reset button, 5v on pin 64, it goes to 0v then to 5v and the screen on the monitor goes OFF for a few seconds and then back to black screen with some small green dots.

I checked the RF connection with my tv giving me a similar result with some noise on the screen. Lastly, I got the DIAGNOSTIC CARTRIDGE connected with a null modem cable on my PC with teraterm but there is no activity either on the console. At this point I am asking for help from here, from you guys, because I really would like to fix this machine and bring him back to life. 

Thank you in advance.

Image2.jpg

Image1.jpg

[exxos]

Jumper on expansion port ?

[Badwolf]

After checking deeper COMBEL IC was only providing 8MHZ to the CPU,

That's normal at boot.

check RESET, HALT & BERR signals to pins 64,129 & 130 - all high with 5volts present. While pressing the reset button, 5v on pin 64, it goes to 0v then to 5v and the screen on the monitor goes OFF for a few seconds and then back to black screen with some small green dots.

That you were able to measure the clock leads me to believe you may have access to an oscilloscope? If so, probe the AS line after reset. Even with the ROM and RAM missing you should get a dozen or so assertions (toggle to ground and back).

Jumper on expansion port ?

I think that tends to yield white screen.

My first guess would be the RAM board. Reseat, reseat and reseat again. Then maybe clean it and reseat it some more. :)

BW

[mikro]

I presume you are aware of https://docs.dev-docs.org/htm/search.ph ... vice+guide ? It provides further hints on what to check (i.e. pins directly on the COMBO IC).

[sdisla]

Jumper on expansion port ?

Thank you Exxos for approving my post.
To your question yes, the jumper is there.

Jumper.jpg

[sdisla]

I presume you are aware of https://docs.dev-docs.org/htm/search.ph ... vice+guide ? It provides further hints on what to check (i.e. pins directly on the COMBO IC).

I have the service guide for reference.

Thank you,

[exxos]

Does the floppy drive light flicker dimly at all ? If it does, then TOS is trying to boot and its likely a RTC fault. If it doesn't then, you have a hardware fault, which could be anything like a bad RAM card , bad solder joints, or a blown Videl chip etc.

Others had similar problems viewtopic.php?f=23&t=2662 but often they don't post if they fixed it or not. Also viewtopic.php?f=23&t=80

[sdisla]

Does the floppy drive light flicker dimly at all ? If it does, then TOS is trying to boot and its likely a RTC fault. If it doesn't then, you have a hardware fault, which could be anything like a bad RAM card , bad solder joints, or a blown Videl chip etc.

Others had similar problems viewtopic.php?f=23&t=2662 but often they don't post if they fixed it or not. Also viewtopic.php?f=23&t=80

Exxos thank you for the links, I had read both of them with details and keep using them as reference.
I will do the floppy LED check later today an provide some feedback.
Regarding the RAM, I got a new one from you 14MB that I swapped with the original 4MB one, but getting the same result.
Regarding solder joins I had done some visual inspections top to bottom of the motherboard, but I will keep looking.
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.

Thank you,

[exxos]

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.

[sdisla]

After checking deeper COMBEL IC was only providing 8MHZ to the CPU,

That's normal at boot.

check RESET, HALT & BERR signals to pins 64,129 & 130 - all high with 5volts present. While pressing the reset button, 5v on pin 64, it goes to 0v then to 5v and the screen on the monitor goes OFF for a few seconds and then back to black screen with some small green dots.

That you were able to measure the clock leads me to believe you may have access to an oscilloscope? If so, probe the AS line after reset. Even with the ROM and RAM missing you should get a dozen or so assertions (toggle to ground and back).

AS is one of the important CPU bus control lines. It signals the start of an access to the motherboard. AS is the 'address strobe' line and means the CPU has loaded an address onto the address bus.

After coming out of reset the CPU will try to read the first two longwords of its address space (address 0 to 8) to get some of is start-up parameters. These four addresses are in ROM (so scoping the ROM's CE (chip enable) pin would be the next step if AS has activity).

Since the Falcon has a 16 bit bus you should see *at least* four separate AS activations even with RAM or ROM missing as these will be read it regardless of their content.

If you don't see these -- the problem is more severe than bad ROM or bad RAM.

Jumper on expansion port ?

I think that tends to yield white screen.

My first guess would be the RAM board. Reseat, reseat and reseat again. Then maybe clean it and reseat it some more. :)

BW

BW,

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.
When the reset button is pressed, I can see some activity, hence I could not get my scope to trigger so I did a picture instead.

AS2.jpg