Micro Genius IQ501 - console with PAL to SECAM converter

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krzysiobal
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Micro Genius IQ501 - console with PAL to SECAM converter

Post by krzysiobal »

I get this console for fixing because it suffered from blinking horizontal bars. My first idea was that the crystal resonator got jitter, but after opening it I couldn't believe what was inside.. a piggyback board with PAL to SECAM converter. This console must have been developed for French or eastern Europe countries.
Image Image Image

I saw this console in at least 2 configurations before, both having 50/60Hz switch:
* With TA-02NP PPU that allows 50/60Hz switch
* With NTSC PPU and external MK5060 50/60 switch
* This one, with classic Dendy chips (UA6527P + UA6538). It also has the 50/60 Hz switch at the back but it is non-functional. After rev-ing the schematic I think it is intended to switch the RF channel instead:
Image Image Image Image Image Image

But the main point of interest is the PAL to SECAM converter of course.
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The PCB consist of unknown chip. The one with non-removed markings is still not known in internet. After restoring the schematics, I have a high premonition that the main 28pin is.. Sony V7021, found in french NES. At lest the GND, VCC, crystal and some other inputs matches. No idea what are the other 4 chips responsible for, but they have legs painted in red/green/blue color, probably to distinguish them after marks had been removed.


The video quality in comparision to PAL is rather poor - colors are dull, noisy and there is some kind of rainbow effect on the right side of objects when color transition changes rapidly from dark to bright:
Image

Anyway, I was curious about the signals going into the chip so I made a ROM that displays 16 vertical colors. The choice was as following, because that way they differ with hue, lumination and saturation:
Image

Here is the difference between PAL signal going to the converter (CH1) and SECAM one going out of it (CH2):
Image

I'm not a video expert but looks like in PAL, the colorust signal phase is maintained between frames, while in SECAM it is altering.

I was curious about the other chips and signals going from/to them, so I checked them against the same fragment of PAL input video line.

V7021:
Image Image Image Image Image Image Image Image Image Image Image

GREEN chip - seems to be some kind of sync detector and forming
green pin 01 = 1.950kHz 29us/484us 0/5V sync with PAL
green pin 02 = 3.900kHz 26us/256us 0/5V sync with PAL
green pin 03 = 1.950 kHz 256us/258us -1.2V/4.8V sync with PAL
green pin 04 = 160mv
green pin 05 = +5V
green pin 06 = 160mb
green pin 07 = 160mv
green pin 08 = GND
green pin 09 = floating
green pin 10 = floating
green pin 11 = floating
green pin 12 = floating
green pin 13 = 1.95 kHz 26us/486us 0/1.69V sync with PAL
green pin 14 = 1.95 kHz 4us/510us 0/5V sync with PAL
green pin 15 = floating
green pin 16 = VCC
Image Image Image Image Image

BLUE chip - no interesting signals were found
blue pin 07 = +5V
blue pin 09 = +5V
blue pin 13 = +5V

RED chip - seems to be some kind of divider
red pin 01 = 5.514 MHz, not synced with PAL
red pin 03 = 2.168 MHz, not synced with PAL
red pin 04 = 1.084 MHz, not synced with PAL
red pin 05 = 0.542 MHz, not synced with PAL
red pin 06 = 0.271 MHz, not synced with PAL
red pin 08 = 973 Hz, not synced with PAL
red pin 10 = 3.91 kHz sync with Pal
red pin 11 = 7.81 kHz sync with Pal
Image Image Image Image Image Image Image Image

HS-7035
hs-7035 pin 08 = -160mV
hs-7035 pin 10 = 5.28V
hs-7035 pin 12 = 240mV
Image Image Image
lidnariq
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Re: Micro Genius IQ501 - console with PAL to SECAM converter

Post by lidnariq »

krzysiobal wrote: Thu Nov 12, 2020 1:27 pm I'm not a video expert but looks like in PAL, the colorburst signal phase is maintained between frames, while in SECAM it is altering.
My understanding is that SECAM is supposed to switch between FM-modulated Pr and Pb on each scanline, each component with its own center frequency a little below the PAL-B colorburst frequency. So it gets the same chroma subsampling that Telefunken PAL has, but uses the 64µs delay line to only hold the other component, rather than adding and subtracting the current scanline from the previous one.
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vortexion
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Re: Micro Genius IQ501 - console with PAL to SECAM converter

Post by vortexion »

Wow. This I have never seen before.

Where did this IQ-501 come from?

That’s definitely a SECAM video signal in channel 2, so this device is converting PAL into SECAM as you say.

I have one of the 50Hz/60Hz switchable IQ-501s using an NTSC chipset and a PAL transcoding circuit, and I also have a native SECAM Dendy using the UM6557 UM6558 UM6559 chipset.

What you have here is something different. It was clearly made after the PAL UMC chipset came into existence, and I would guess before the SECAM UMC chipset was made. I suspect this device generates much better SECAM than the native SECAM chipset does.

Do you still have this machine?

Richard Atkinson
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vortexion
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Re: Micro Genius IQ501 - console with PAL to SECAM converter

Post by vortexion »

Just to give an idea of what that circuit has to do:

1. Decode PAL composite video, by separating out Y (the luminance) and C (the chrominance) and decoding C to R-Y and B-Y.

2. Generate frequency modulated carriers for R-Y and B-Y, using 4.40625 MHz as the centre frequency for R-Y and 4.25 MHz for B-Y. It only needs to generate one of these at a time, so the circuit may only have a single frequency modulator circuit.

3. Combine Y and the new C signal, consisting of alternating lines with R-Y and B-Y carriers, and output that as composite video.

There are a few complications with SECAM that this circuit may or may not bother with. Pre-emphasis is supposed to be applied to R-Y and B-Y before modulating the carrier, and the resulting carrier should go through a notch reject filter (called an anti-cloche filter in a lot of SECAM documentation) centred on 4.286 MHz - but the native SECAM Dendy doesn’t do any of this and this circuit may not do it either.

From the look of the carrier in channel 2, the amplitude is constant so there is no anti-cloche filtering. On the native SECAM Dendy the picture can suffer from “SECAM Fire” on cyan colours, even with a direct baseband video connection, and I think this is because of the lack of an anti-cloche filter. (Also known as high frequency pre-emphasis in some SECAM documentation)

This SECAM Fire shows up in Cutman stage in Mega Man on the native SECAM Dendy. I wonder, does it show up on this machine?

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vortexion
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Re: Micro Genius IQ501 - console with PAL to SECAM converter

Post by vortexion »

krzysiobal wrote: Thu Nov 12, 2020 1:27 pm

The video quality in comparision to PAL is rather poor - colors are dull, noisy and there is some kind of rainbow effect on the right side of objects when color transition changes rapidly from dark to bright:

I'm not a video expert but looks like in PAL, the colorust signal phase is maintained between frames, while in SECAM it is altering.
Hi krzysiobal,

Just a few comments about your original post. I have observed the "rainbow effect" on the right side of colour transitions in the native SECAM Dendy, and I think it's a form of "SECAM Fire". I'm not 100% certain of this, but I think what it is happening is that the FM decoder circuit in the television's SECAM decoder is momentarily losing track of the FM carrier for some reason. The R-Y and B-Y signals are supposed to be band limited to about 1.3 MHz which puts a limit on how fast the carrier can change frequency. If the frequency changes faster than this, there could be more FM sidebands outside the range of the SECAM chrominance signal that is input to the FM decoder, and the amplitude of FM signals within the range could be reduced. This could cause the FM decoder to momentarily lose track of the FM carrier.

Regarding the colour burst, the PAL colour burst ought to be generated at the same point every line, which in colour cycles is 284 1/6 cycles later. The PAL colour burst has two phases, for +V lines and -V lines, which are output on alternating lines to give a six line pattern. Three 135 degree colour bursts starting at 0, 120 and 240 degree offsets, and three 225 degree colour bursts starting at 60, 180 and 300 degree offsets. (341 PPU dots per scan line, 1705 master clock cycles, 284 1/6 colour cycles)

SECAM doesn't have a colour burst, but what it does have is continuous FM carrier throughout the entire line except for the sync pulses. The carrier is present during the back porch, throughout the visible line (including all black areas) and during the front porch. The instantaneous phase of the carrier contains no information in SECAM, nor does the amplitude. The only thing that matters is the frequency, which can be thought of as being related to the time between successive peaks of the carrier (frequency = 1 / period).

What happens to the phase of the carrier between successive lines depends on how the carrier is generated. On the native SECAM Dendy, the FM carrier is generated digitally using a phase accumulating oscillator, and it looks like the carrier starts at the same part of the cycle on every line. Because it uses FM, the number of cycles of carrier and the phase of the carrier at the end of the line depend on the colour information in that line. But when it starts the next line, the phase is reset to the same point at the start of the line.

Some other SECAM encoders use voltage controlled oscillators to generate the FM carriers, and so their behaviour can be much more unpredictable. There is a SECAM version of the Commodore 64 computer which contains a PAL decoder and a SECAM encoder, and the oscillator(s) on this SECAM encoder exhibit very analogue style behaviour. They drift as the device warms up, causing the hues to change (!), and there's no attempt to start each line at a defined phase of the carrier.

The SECAM standard does actually specify a particular pattern for how the carriers start on each line, but the purpose of this is to reduce the appearance of the carrier on monochrome receivers that pre-date the introduction of colour, and SECAM decoders don't need this exact pattern to be present to decode valid colour.

"The phase of the subcarriers is also reversed 180° on every third line and between each field to further reduce subcarrier visibility." page 108 of http://goelectronics.weebly.com/uploads ... 1/ntsc.pdf

Richard
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