Thomson To9 no video

[Stellaris]

Good evening folks!
I am trying to get working two Thomson machines, TO9 and TO8.
Here I will ask you help about the TO9.
The machine was with no power and the power supply had two blue capacitors fired. I replaced all the capacitors with the exceptions of three big ones.
I cleaned the motherboard and the machine was working just fine.
After a coupled of days when I went back to the pc it power on, the red light is on, on the screen there is the signal but it is black. I say that there is the signal because when I switch it off the black change to a more dark and the TV say no signal.
Any tips?
Thanks a lot.

[__sam__]

May be it is the SCART which isn't correctly plugged, or has a bent or oxidized pin ?

[Stellaris]

I tryied with a different cable, a different TV and plug in and out several times. Same results. The pc react to a reset with the red light of the cups button on and off when pressing.
The only strange happen just before the problem when I was using a floppy with a game. After pressing B there was a message about memory error but the basic was reacting to commands.
I switched off and then after one hour when I went to switch it on again it showed the problem.
Now I replaced all the capacitors from the motherboard.
Nothing. I cleaned all the contacts. Nothing.

[__sam__]

IIRC the caps-led on the keyboard is handled by a separate CPU. So, it might still react when the main CPU hangs.

[Stellaris]

This is not a good news for me.

[Daniel]

Did you measure the voltages at the output of the power supply

[Stellaris]

no. Do you have a pinout with the values?

[Stellaris]

Ok, I got the power supply schemas from http://dcmoto.free.fr.
Attached there is the values that I got rounded by the red square close to the must values.

ThomsonTO9PowerSupply.jpg (53.15 Kio) Consulté 3683 fois

I assume that there is problem with the power supply. This should be easly fixable, but I hope that something on the motherboard got not broken from the 6V insted of zero!
Any advice how to proceed?
Thanks a lot

[Daniel]

Your pinout is wrong. This is the correct one :

1= -5V
2= GND
3= +12V
4= GND
5= GND
6= GND
7= +5V
8= +5V
9= +5V

to9-power-supply.png (51.05 Kio) Consulté 3679 fois

[Stellaris]

I see. So the wrong value is, in my case, on pin 3 that should be +12v while I have +6v

[Daniel]

This is possibly the cause of the video problem.

[Fool-DupleX]

The two fried capacitors on the PSU is a known problem on these machines, it's benign. There's really no need to change all the other capacitors.

Not sure about the video. the +12V is used only for the switching signal on SCART. It has no other purpose. If the TV switches … the signal is ok. However, on modern TVs, it has to be +12V to detect a proper 4/3 ratio (Under 9V, it's 16/9). So this should be fixed still. Have you measured the voltage with the PSU disconnected or connected to the mainboard ? When it is connected, the +5V MUST be around 5.02, but certainly not less than 5V and not more than 5.5V.

If the screen remains black, obviously the CPU does not start (but it did in the past, right), it could be just as easy as resocketting the CPU or the ROMs. I would try that first.

Edit, you said :

After pressing B there was a message about memory error but the basic was reacting to commands.

This message is a very strong indication that one of the RAM chips is fried. This is something quite common after 30 years on these machines. I just repaired a TO9 with this problem last week. It could be the source of the problem also, but not necessarily (especially since your machine worked despite the message). The most common symptom with RAM error is strange color patterns on the screen.

[nicolho]

If the screen remains black, obviously the CPU does not start [...]

Hi Fool ! Could it be just related to the video circuitry (I mean any chips specifically involved in image output) so the CPU could still operate without display ?
When it happens on an MO5, we could know this easily if 'beep' sounds could be heard when pressing the keys... Stellaris could make a similar test, even without visual feedback, following these simple steps (not totally sure, because I've only tried them in an emulator ) :
- wait a few seconds after powering up the TO9 and press 4 so it goes to the BASIC 1.0 console
- wait another few seconds for the BASIC to load, then type BEEP and Enter, which should give a beep on TV speaker (via SCART) and on the audio output RCA connector at the back as well (useful to check with some amplified speakers or connected to a sound system, if there was a problem with the TV output). Obviously you can type the same command again.

In that case, it would be interesting to observe with an oscilloscope if the video sync signal (generated by the Gate Array Circuit Machine, according to the schematics) is present on SCART (pin 20) or its internal connector (BW07, on pin 8 ).

[Fool-DupleX]

You can try that for sure. But if you have an oscilloscope (I do), you do not need to make all these tests at all. Go straight to the point and test the vsync, the clock, the reset and the address bus of the CPU and you'll know immediately where the problem lies.

However, Stelaris has a very particular description of the black screen. He says it's "light black" so to say, which means that the machine does produce a full picture. Also, on a modern tv, no sync is generally detected and a message is displayed.

The gate-array responsible for displaying the picture is initialized in software by the CPU. As long as it's not initialized, you get a "light black" picture. This is why I concluded with the CPU not running. Note that it's not necessarily because the CPU is out of order. It can be the ROM where the initialisation code is stored. Or the reset line could be stuck for some reason. The clock is probably OK because you would not get the "light black" picture otherwise (serialisation of the RAM to the scart always runs as long as there is a clock signal).

But before trying anything else, the very first thing to make sure of is the voltage levels *on load*, i.e. with PSU connected to the mainboard. On the Thomson machines in general, they are ideally set at +5.02V, +12.10V and -5.02V. The +12V and -5V are not that important, but the the +5V is especially critical. Below 5V, the machine will be unstable. Over 5.5V, it gets really dangerous for the chips.

[nicolho]

Ok, thanks for this detailed and logic explanation. Sorry, I didn't pay enough attention about Stellaris' description of his black screen, indeed a sync signal is probably present.

I proposed the "keyboard beeps" test because it is easy to do and can be tried without any electronic instrument (obvisouly an oscilloscope could be used after that, or from the start). If sound was working, it would only mean that the problem is limited to the ""pixels generation circuitry"", yet that would at least exclude the CPU and ROM chips (amongst others, partially working at least)...

But you're right, it looks like this TO9 initialisation fails at some point, before the video chips are properly configured by software.