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I don't think it's a RAM issue as the same screen appears each time. Each flashing cursor on the screen shows the same character. I see two blinking cursors which mirror each other when I type, but only a handful of keys bring up the correct character on the screen. It's not random, I get the same screen at each power on. I no longer see any RAM failure flashes while using the Dead Test cartridge, BUT I am now seeing a new fault No more voltage drop across the switch I now have 40mV drop across the board which sounds about right for this older board. pins with blobs of solder to bypass the switch. way way too much!Īs a quick diagnostic check I simply bridged the N.O. I'm measuring 200mV drop across the 5V side while it's switched on. Instead of a nice 4.87-4.9V across the board, it was getting down to 4.5-4.6V.Īfter poking and prodding around the board it turns out the power switch is the cause of the voltage drop. The between the DIN socket and the User Port was over 200mV!! This would explain the weird coming and going RAM failure issues. I've rechecked the 5V power rail across the board and found that it was measuring lower than it should by a significant amount. OK, after a few days of being distracted by work and family I am taking a fresh look at the this board. These look factory original (no obvious rework).Ĭan a RAM chip be partially bad or is this fault likely caused by something else on the PCB that has failed? It has 4x MN4164P and 4x M3764 memory chips on board. Strangely sometimes the RAM test passes fine and sometimes it shows different RAM chips as bad. I recall that a faulty SID will also cause a control port to show as bad (no paddle inputs). The time on the bottom right of the Diag Cart screen is not incrementing which points to U2 as being faulty. It looks like I also have at least one bad 6526 as well (U2).
#MEMORY DIAG TEST SERIAL#
Number one is a dead SID chip, it makes no sound! It also shows that Cassette, Control Port, Serial Port, User Port, Timer 2 A & B are bad. It has a 250407 PCB in it that is showing some hardware issues while running the C64 Diagnostic Cart and Harness. It does sometimes power up with the normal C64 screen, but also randomly shows the dreaded "Out of Memory error in 0". Tablet and Smartphone users touch only repeated images.
#MEMORY DIAG TEST PC#
When an image is repeated: PC and laptop users press the space bar on your keyboard when you see a repeated image. I had heard of these cases before but had never seen one in person until now. Test your short term memory performance with these online screening tests: A series of images will appear during the test. Interestingly it has a custom replacement C64C style case that was made locally here in South Australia.