Lately I have been seeing many Amiga 600 and Amiga 1200 with bad Band Pass Filter (Z221) and Delay Line (Z222). This generally causing bad picture quality on composite and the RF-modulator.
There are many suggested solutions out there but none that really replaces the Z221 and Z222, until now. While attending to Datastorm 2018 I talked some with TBTorro and he said that he had done some tests with CXA2075 which was the high end version of the original CXA1145M which is the one used in Amiga 600 and Amiga 1200.
The modification is rather simple if you have some SMD soldering experience and you only need to components. So, why wait!
Bill Of Material
|1||CXA2075 RGB Encoder||SOT|
|1||2.61 kOhm 1% Resistor||Through hole|
CXA1145M vs. CXA2075M
The pinout is more or less 100% compatible between CXA1145M and CXA2075M. The main concern pins are Pin 8 and 9 on CXA2075M that is Audio In/Out on the CXA1145M and Pin 17 that is where we can enable the internal Trap which acts as the replacement for Band Pass Filter and Delay Line.
In my example I will show you how it is done on an Amiga 1200.
Start preparing the CXA2075M by cutting pins 8 and 9 as the picture show.
Remove the old CXA1145M from the Amiga 600 or Amiga 1200 mainboard. You can also remove Z221 and Z222, but we will disable them so it is really not necessary.
Flip the mainboard on the Amiga 1200 and locate the following area near the IDE 44 connector.
You should remove any of the following SMD components at this area. Note that some of the SMD components might already be removed from factory.
The de-soldering of SMD capacitors and resistors could be looking like this (pre-cleaning). Please be careful when cleaning the pads with solder wick. If you are using to much heat and pressure, you might damage the pads.
Clean the pads and add some flux of your choice and then put the CXA2075M in place. Attach one corner with solder, adjust the chip and put some solder on in the opposite corner of the CXA2075M.
When you are happy with the positioning of the CXA2075M, solder the rest of the pins to the mainboard, I these cases I prefer to perform a so called drag-soldering.
As you can see, I have already removed Pin 8 and 9 before soldering the chip onto the mainboard.
When the CXA2075M has been soldered to the mainboard, do a solder bridge between Pad 8 and 9. In my case I used a very short piece of the pin from the resistor.
This can also be done before the CXA2075 is soldered to the mainboard of course.
Prepare the 2.61 kOhm 1% resistor as following. Be aware so you don’t cut the pins too short.
Solder the 2.61k Ohm resistor between Pin 12 and 17 on the CXA2075M. This will add a Pull-Up so the internal TRAP switch is enabled and the CXA2075M will use the internal Band Pass Filter and Delay Line.
The final result should look something like the picture below. Be sure to connect between the mentioned pins, else you can damage your Amiga.
Alright, it is time for some testing. I hooked up my Amiga 1200 to a LCD TV with an RCA-cable between the composite port on Amiga 1200 and the LCD TV.
Power on the Amiga… Waiting… Waiting…
Holy shit! The result was probably one of the best quality pictures with composite I have ever seen. See for yourself!
And yes, the Mumin coffee cup is kinda of a thing I do 🙂
Well, I am super happy with this solution. The picture quality on the composite is now better than ever on my Amiga and I have more or less throw away any bad Z221 and Z222 that I find in the future and simply replace them with this solution.
If you have a working composite, please I would say it is not worth it unless you are a perfectionist 🙂
Over and out!