My Falcon went to black screen

[christophe.griard]

Hello Sety,

Thank you very much for your message...

First, I checked the reset operation:
- when I press the reset button on the back of the Falcon, pin 17 displays a - 5V which quickly goes to 0v.

Concerning RAM, when I had the problem with the screen going black, I had a 16MB RAM card.
Before this memory upgrade, I had a 4MB card (with memory components directly soldered to the card, while on the 16 MB memory card there is a SIM card installed on the board). I know that the 4 MB card worked before switching to the 16 MB board and it is with this 4 MB card that I am currently diagnosing the Falcon.

As I initially thought it could be a RAM issue, I ordered a new memory card from Exxos store (without the SIM RAM), so I'm 100% sure of the RAM card. But regarding the SIM RAM, I put another 16MB SIM RAM that I already had (in case the SIM RAM which was installed when I had the issue is defective) : I am not 100% sure of this 16 Mb SIM (I was told it works but I have never tried it before so I can't be 100% sure ...).

I have despite retried the two 16 Mb memory boards today and the only thing I can see is that I have an all black screen with the two 16 Mb cards while I have strange green stripes with the 4mb board... I made several tests and these observations are not random and are reproducible.

For the green bars, I put a photo of the screen with the green bars at the very beginning of this post.

Like Exxos and Mikro, you help me diagnose my Falcon and it's already very nice. It’s really nice of you to offer to lend me a memory card to make sure it’s not a memory issue.

Even if his shop is closed at the moment, maybe when Exxos reads the post he can tell me if I can buy one from him to avoid you lending me one (unless you have several SIM and I can buy one from you).

You will tell me if the behavior of the reset I observed is correct. On my side, I will look again at the signal on pin 18 to see if the processor is in "HALT" or not.

Thank you again for your help in bringing my Falcon back to life: I really appreciate...

I wish you a nice end of the day.

Christophe.

[christophe.griard]

Hello,

A small update : I checked the HALT signal on pin 18 :

- just after power on, signal at +5V that goes rapidly to 0V
- just after reset -5V that goes rapidly to 0V.

In the service guide, it said that HALT signal should be TTL high (if not there is a bad reset circuit, a double bus error or a bad CPU) : so should I understand that the signal should be at +5V on pin 18?

I removed the ROM (TOS 4.02) and replaced it with a 4.04 which I know it works (I also cleaned the contacts in the ROM support also in case ...) and same result...

[PhilC]

Halt should be high ie 5 volt. It's written /halt which means not halted

Same for the likes of /berr

So if you can see a blip of 5v high on the scope at reset and then it goes low, then it's trying to reset but something has halted the cpu, the harder bit is to find out whether it's the cpu or another device halting the system.

[christophe.griard]

Thanks a lot PhilC for these explanations.

At least, betwwen the clock frequency that is only at 8Mhz on the Pin 23 of the expansion port instead of 16 Mhz, and the fact that the HALT signal is at 0 instead of +5V, I better understand the non response of the system since it is halted/stopped...

As you say, the question now is to discover why the system is halted...

I went to my desk again and I just had a look to the signal on pin 19 (Bus error) : service manual indicates that the reason for an halted status could be either an faulty reset circuit, a faulty CPU or a double bus error.
The signal is at 0V on this pin 19 and as the service manual says it should be high, it seems that there is a bus error...

I made several test and one or two times I saw a +5V but very rapidly it goes to 0V. Pushing the reset button does change anything on the signal...

At this point, to be honest, I'm not sure what to look for to try to understand why the system is stopped ...

[Tomswork]

There a falcon for sale on ebay and maybe a motherboard

Tom

[sety]

The signal is at 0V on this pin 19 and as the service manual says it should be high, it seems that there is a bus error...

I made several test and one or two times I saw a +5V but very rapidly it goes to 0V. Pushing the reset button does change anything on the signal...

At this point, to be honest, I'm not sure what to look for to try to understand why the system is stopped ...

Is the cpu unusually hot or unusually cold? Ditto for other ICs on the board.

Do you have a test cartridge? If you can get one and set up a null modem cable and serial terminal, with any luck it might spit out an error code via rs232 before the cpu halts and help to narrow the fault.

Cheers

[christophe.griard]

Thanks Tom for the information. I just saw the memory board with 16 Mb of RAM. I will try to bid...

[christophe.griard]

Hello Sety,

Concerning chips temperature, I noticed that CPU is warmer (not very hot but hot) in comparison with COMBO and VIDEL for example. I made temperature measurements with an infrared thermometer : with the same inital temperature of 25°C, after 2 minutes I reach a stabilized situation with a CPU at 30°C, a COMBO at 27°C and a VIDEL at 26°C. By touching the CPU with a finger, I can clearly feel the CPU is warmer than the COMBO and the VIDEL.

Concerning the diagnosis cartridge, this is the first thing I did by plugging such a cartridge with a null modem cable connected between the Falcon and an ATARI STE running the VT52 terminal emulator but nothing appears on the VT52 terminal... Unfortunately...

[christophe.griard]

Hello,

I made another measurement on pin 24 and 25 of the expansion port (Vcc) and if just after power on the Flacon, the voltage is at +5V, very rapidly it goes to 0V.

The reset pin shows a +5V just after power on and then rapidly goes to 0V (instead to be "High" in normal operation that is to say +5V (Sety information; like for Bus error pin and HALT pin).

So I must have a look at the reset circuit that may be the root cause... I will try to see if I can diagnose the reset button without desolder it from the motherboard.

At least, following Sety advice, and after temperatures measurement, I let the Falcon on for 10 minutes to see if the CPU becomes warmer and warmer (it is said in the service manual that if one can not let his finger more than 1 second on the CPU, probably the CPU is faulty.
And after 10 minutes, the CPU is not very hot : I can let my finget without any trouble for my finger and the temperature I measured with an infrared meter is 33°C with an ambient air at 27°C. So CPU should be ok...

[christophe.griard]

I just ordered a 16 Mb SIM and 2 reset switches (one potentially for the Falcon and one for spare).