Mindset repair

[daver2]

>>> My god.. what is in those things!

WMD...

>>> I would have thought interlacing would be mentioned in the documentation or brochure somewhere..

It may be more to do with the modification (aka video production) rather than a 'standard' feature. That's what I am thinking off the top of my head.

Dave

[falter]

Yeah I kind of suspect. It'd be rare for two machines to have exactly the same fault.. unless it's a weak link common to both.

The manual I read was specific to the 'video production' variant. But who knows.. the 'sync' board on each machine is different.. one is only about half the size of the one pictured. Who knows what on the fly mods were being made. The machine I'm presently working on has about 6 or7 jumper wires on the bottom between different ICs.

[Chuck(G)]

Sure. Soon as the magic smoke clears from my office. Apparently I forgot about a RIFA cap. My god.. what is in those things!

Mineral oil, mostly. The rest is foil and paper. The encapsulation is resin.

Nothing you haven't seen before and mostly harmless.

[rittwage]

I've seen two other Mindsets in my travels, and both did not work in the same way yours does not (black screen, occasional video nonsense). I think they just fail. I would definitely spend some effort to see what could be done if I owned one, though. Maybe check/replace the RAM first since that is easily sourced...

Is the Mindset in the MESS emulator yet? If so, you could modify the source the make the emulator RAM faulty and see if it results in a black screen. Just ideas... It may not mean anything since I doubt the system is emulated 100%.

[falter]

Yeah, I've got a bad feeling this is maybe the custom video chip. Interstingly, the half of the RAM that isn't clocking or doing anything is right beside it.

It's like the sound chip - there's nothing happening on its XTAL pins... I even tried wiring in a 12mhz crystal directly to them and zero.. but if I move the chip to the socket the keyboard plugs into, there's activity there.

So I'm not sure if those two things show something is broken, or if they are normally not initialized/activated to a certain point in the post process, because something further up the chain is broken. But without a working unit or theory of operation to clear things up, I'm kinda stuck.

[daver2]

Do we have a manual or a schematic anywhere you are aware of by any chance?

Sorry, brain fade, bitsavers - duhhhhh!

Dave

[daver2]

So, the 8042 microcontroller can be clocked in one of two ways:

1. Pin 2 is connected to 0V/GND. In which case an external clock is fed into pin 3.
2. A crystal is connected between pins 2 and 3.

What do you see on your PCB?

No schematic in the manual unfortunately. We'll have to do this the 'old school' way!

Dave

[falter]

What I see for the sound controller 8042 is pin 2 is connected to one side of 12mhz XTAL (Y2), and pin 3 is connected to both the other side of the same XTAL as well as one side of this little cap C12:

20191117_122919.jpg

There is no activity on either pin. For an experiment, I tried wiring up another 12mhz crystal I had manually to pins 2 and 3, grounding it on its case.. but same thing. Then I moved the 8042 to the other 8042 slot and powered up.. just to see if there was any activity on those pins or if something was messed with the chip. There was clock signal there.

I've been going over the datasheet.. it doesn't seem to me like there'd be anything to trigger it on and off.. I would assume the clock would need to be running for the chip to do anything..

I don't know how many layers this board is either or what else might be connected. I suspect there is a ground or 5v plane sandwiched in between sides because I cannot see anything that the other side of C12 connects into on either side of the PCB.

[daver2]

With the power switched OFF you should be able to trace the wiring with your multimeter set to read Ohms.

Pin 2 of the 8042 should only be connected to one side of the 12 MHz crystal.

Pin 3 of the 8042 should only be connected to the other side of the 12 MHz crystal and one side of C12.

Neither pin 2 or pin 3 of the 8042 should be connected to 0V/GND or +5V.

The other side of C12 should be connected to 0V/GND.

Has your machine got an RS232 serial port fitted by any chance?

The PCB has probably 4 or 6 layers.

Dave

[daver2]

When you say 'video production' module, do you have the external unit with the fader or not?

I see an 'external synchronisation' cable that must be fitted between the two units etc.

Dave