[MZ-700] Modding a SCART>HDMI to output RGBS on modern TV
Posted: Sun Feb 04, 2018 12:05 pm
I have bought this converter because I was told they work pretty good with RGB output for AMIGA. I also read an article about the synchronization issue with Atari when using a SCART on modern TVs and to address it by modding this converter so I decided to buy another one as I was expected to get a similar issue with MZ-700 and MZ-800.
Here is the converter: This converter accepts RGBS source and composite (CVBS) source but not S-video source. In our case, only RGBS matters. Beware, there are a lot of SCART>HDMI converters out that don't accept RGBS source through SCART. At least this model does.
Here is my work environment: .
You can see I have an endoscope plugged into an embedded PC which displays on my modern TV. The circuit of the converter is quite small so this camera is a handful device.
The idea is to use this converter to provide fast switching with the voltage that goes well so that the TV receives well in RGBS.
The idea is all the more attractive as I could make myself a SCART cable for the MZ-700 (or even for the MZ-800) which will have the same problem of not being able to provide the right signal for fast switching in RGBS. If this converter does the job instead, I could use this converter for both the Atari 520 STE and the MZ-700 not caring about fast and slow switching signals (the latter can be ignored by forcing the 4/3 TV).
But there is a problem. The circuit of the converter has obviously changed since the last update of the tutorial I link here. The link states that a trace must be cut between the fast switching pin and the first 75 Ohm resistor connected to the ground in parallel. Just after this resistor, there is a ZD1 diode where we must add a wire connected to a source of 5V with a serial 100 Ohm resistor. Now, this diode is no longer!
So I tried to follow the trace: it goes through the same 75 Ohm resistor connected to the ground in parallel. So I guess I just have to cut it. However, on the other branch in parallel, there is no more diode and the trace drives straightly to a pin of the big processing chip.
The circuit with the 'FAST SWITCH' trace drawn in red: .
The voltage applied to FAST SWITCH must range between 0,3V and 3V so the SCART should use RGBS signals and not composite ones.
Now, I have two solutions:
1) Steal a 5V pad and turn it into a 2.15V to feed the big chip:
On my circuit, there is nothing after 74 Ohm resistance. We can try a voltage division that looks like this: where VIN = 5V, R1 = 100 Ohm and R2 = 75 Ohm.
As a result, we have: VOUT = 5V * (75 / (100 + 75)) = 2.15V.
Which gives us: .
---TO BE CONTINUED---
Here is the converter: This converter accepts RGBS source and composite (CVBS) source but not S-video source. In our case, only RGBS matters. Beware, there are a lot of SCART>HDMI converters out that don't accept RGBS source through SCART. At least this model does.
Here is my work environment: .
You can see I have an endoscope plugged into an embedded PC which displays on my modern TV. The circuit of the converter is quite small so this camera is a handful device.
The idea is to use this converter to provide fast switching with the voltage that goes well so that the TV receives well in RGBS.
The idea is all the more attractive as I could make myself a SCART cable for the MZ-700 (or even for the MZ-800) which will have the same problem of not being able to provide the right signal for fast switching in RGBS. If this converter does the job instead, I could use this converter for both the Atari 520 STE and the MZ-700 not caring about fast and slow switching signals (the latter can be ignored by forcing the 4/3 TV).
But there is a problem. The circuit of the converter has obviously changed since the last update of the tutorial I link here. The link states that a trace must be cut between the fast switching pin and the first 75 Ohm resistor connected to the ground in parallel. Just after this resistor, there is a ZD1 diode where we must add a wire connected to a source of 5V with a serial 100 Ohm resistor. Now, this diode is no longer!
So I tried to follow the trace: it goes through the same 75 Ohm resistor connected to the ground in parallel. So I guess I just have to cut it. However, on the other branch in parallel, there is no more diode and the trace drives straightly to a pin of the big processing chip.
The circuit with the 'FAST SWITCH' trace drawn in red: .
The voltage applied to FAST SWITCH must range between 0,3V and 3V so the SCART should use RGBS signals and not composite ones.
Now, I have two solutions:
1) Steal a 5V pad and turn it into a 2.15V to feed the big chip:
On my circuit, there is nothing after 74 Ohm resistance. We can try a voltage division that looks like this: where VIN = 5V, R1 = 100 Ohm and R2 = 75 Ohm.
As a result, we have: VOUT = 5V * (75 / (100 + 75)) = 2.15V.
Which gives us: .
---TO BE CONTINUED---