Quantel PaintBox Restoration Part 3: ( 7001, 1983) (Warning, technical video lol)

I am also on Twitter too if you want more insanity in your life,have a website showing all my vids, my collection and a blog etc, and a Facebook group :o)

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[PiepsiPanic]

"Speak up, the Paint Box is too loud!!" - "What did you say? Can't hear you, the Paint Box is too loud!!" *lol*

[electronash]

Yep, outside of BNC is the ground / shield. It normally connects through the shield / braid on the cable(s) inside the SCART cable.

I had to hook up my Quantel Harriet to the SCART socket as I didn't buy a broadcast monitor for it. I took +5V from inside the Harriet for pin 16 on the SCART, but I added a 100-ohm series resistor for safety (there is a LOT of current available from the PSUs when something shorts out!)

[electronash]

Quick tip about the o'scope - The central "twiddler" dials on the volts/div and timebase which let you "zoom in" on the signals usually have a position where they click into place (often at the top end of their range); unless you click them into place, the volts/div and/or timebase value is not calibrated and are basically meaningless. :)

In the "Problems 2" vid, it didn't look like the timebase central dial was clicked, so the timing of the signal was a weird value.

[electronash]

We're still after any suggestions though. :)

It may be something simple like a dodgy DIP switch, or that it always needs an external sync signal before it will start up properly (the Installation Manual does mention this).

In the next few days, Steve says he might hook up the composite output from an Amiga (or one of his many computers) to the Paintbox's Sync input to see if it locks on.

[electronash]

At 8:31, this is at 10mv/div, so the Main signal is only around 20mv peak-to-peak. This is tiny - a normal PAL signal is around 1000mV (1 volt or so p-p, maybe a bit higher).

(btw, if volts/div is on "mv", this is millivolts, not microvolts) :)

At 12:33, this is a proper nice looking PAL composite signal. It's at 0.5v/div, so the signal is around 1.5 volts p-p. It seems a tiny bit high, but this might be due to those evil twiddlers!

[RetroGamerVX]

No intro on this one, takes ages to render the intro and outro and I wanted it up tonight :o)

[laurdy]

to get a signal lock on the scope: make sure that the trigger is set to the correct input channel, check for the correct triggering mode and then set the trigger level

[RetroGamerVX]

Thanks Laurdy, the trigger setting is knocked out of alignment inside the scope, I know this because I knocked it myself and do not know how to put it back properly. I have a second scope so hopefully that can help :o)

[electronash]

The H/V syncs from the CRTC go through a few logic IC's and a PLL chip, and will need to be combined to comp sync too. Not sure where that happens yet.

I'll ask Steve to do a vid showing the 'scope shots of the EPROM address / data pins soon. He says there is data whizzing past on most of those pins, so the CPU is doing something at least?

A quick way to test the RGB outputs is to add a cap between Sync out and one of the colours. This should get a stable picture on the TV's composite input.

[electronash]

Yeah, I was a bit bored last night, so I just rambled on here. lol
I hope I didn't scare anyone off. Like I said, any suggestions would be welcome.
I'm just letting people know what you've found so far.
Don't worry about the Black Burst stuff, I'll have that sorted soon. Or, just a BBC Micro might work well for now.

[RetroGamerVX]

Wow, you have been thinking about it a lot :o) I've read it but will discuss it tomorrow or Thursday, depending on how the Replay project goes, but if more money needs to be spent on it, I will have to put it on the backburner until at least after Replay :o(

[pferreira]

Meanwhile next door the neighbours think Steve is conducting government experiments...

[electronash]

A "Black Burst" is a composite signal with just the sync / colour burst, and the image part of the signal set to the "black" voltage level.

You could probably generate that from a retro micro, or anything with a "blank" image on a composite output. It might even work by just connecting the Sync output into the Black Burst input??

[electronash]

...at 12:33, the timebase is 5µs/div...

This would mean around 20µs between the sync pulses, so something is dodgy there? Pretty sure the 'scope is set wrong because I doubt the TV would even sync if the signal was running that fast.

(The width of a normal PAL line is 64µs.)

The install guide shows the Black Burst specs under the "Locking Reference" heading, so Stu may have the answer - it needs a reference signal on the Black Burst input to lock on to! :)

[RetroGamerVX]

I'm told that this kicks out an old rgb (15khz) so may not be recognised, but that's something I'm gonna try tomorrow. :o)

[Galfonz]

Static zapped probably. That old equipment was much more sensitive than modern stuff.

[electronash]

There's also a Rockwell R6545 CRTC chip (Motorola MC6845 clone) on the CPU1 board which outputs the basic text info for the "Digital Display" port. It doesn't look like there is any proper output at all from that port, so it doesn't look like the CPU board is starting up properly?

You'd at least expect the Hsync / Vsync outputs from the CRTC to be working. Many of those chips will output sync even with just the clock connected (not always the case though).

[electronash]

...if you find you need to use very small volts/div like on the Main output, most of the time these signals are likely just crosstalk or leakage and are not at a high enough level to be considered video signals!

It could point to a possible fault with the Main output, or it could just be that the PB isn't locked to a Sync input and has disabled the Main composite output...

[retrokitUK]

Been doing some reading. The BNC shields are the GND connections. Sending a link to you via twitter...

[electronash]

My hunch is that the RGB outputs will be similar to the comp vid image from the Aux output though.

By the look of the screenshots, the framestores aren't being initialized properly. The image appears too fast for the CPU to have written to the framebuffer already (I doubt it anyway).


The Aux output confirms the PAL encoder and sync is probably working fine. I don't think the Main output is giving anything useful - the voltage level is so low that it could just be leakage from the Aux output.