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About RTBaker

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    Combat Commando
  1. Hi, Looking for some hardware repair advice regarding my XEGS. I brought it on Fleabay as 'working when I put it away but unable to test before selling' - not surprisingly its dead. On power up there is no sound and no video output. There are some 0.5v pulses on the video output which occur at PAL line rate but they are too small for a tv to lock on to - no video data is present. After opening it up +5V was on all the IC's and none of the IC's get hot so I had a look at the Sally 6502c processor with my scope. I found that there is no activity at all, even on reset, which works ok, on either of the data and address busses or control lines. I found the following: (3) phi0 - permanently LOW (37) phi2 - clock I/P working (coming in from Freddie) (39) phi2 - clock O/P sitting at 1.2V (7) SYNC - permanently low - even with reset no activity at all (34) R/Wbar - permanently low (2) RDY - this is really weird - It starts High on reset but then gradually drops to Low over about 30 seconds (4) IRQbar - this changes state after about 30 seconds This is shown in the scope photo below where yellow trace is RDY and Blue is IRQbar I see from the schematics I have that the RDY pin just goes to the ANTIC. It is also labelled as leaving that sheet but I cannot see it being used anywhere else. There is something amiss here but is it the ANTIC, SALLY or something that could be at fault - could anything else cause the weird RDY signal? As I don't have any spare IC's I wondered if anyone could offer me any advice on what to do next to narrow the location of the fault before I start buying replacement IC's. Thanks for your help
  2. Hi, Can anyone direct me to a copy of the 4port bios rom? Thanks for you help
  3. Hi, I was just wondering if anyone had the schematics and/or a service manual for this unit? I've looked all over the inter webs and come up with nothing! Thanks for your help Russell
  4. Forgot say the ROM has printed on it 1983 Coleco R72114A 8316 Thanks
  5. Hi, I have just blown the Final Test Cartridge (19xx) into an eprom and plugged it into my ColecoVision. Everything works fine but the ROM Checksum comes up as bad showing BE86. This is a UK unit and I was wondering if they came with a different rom to the US one that, I assume, the test program is looking for? Does anyone know what the checksum should be for a UK unit? Thanks
  6. I did put in sockets so I was able to check out all of the memory lines between the memories and to the graphics chip - they were all OK. I then thought to check out the power supply I was using and found that it tops out at 500mA so I changed it for the 1.5A unit I use with my Raspberry Pi. With the new power supply all is well and all of the lines have disappeared! Thanks very much for all the suggestions and help
  7. Thanks for the advice - I'll try to double check all the traces with a multimeter to check continuity between all the VRAMs
  8. Hi, I have just spent a few weeks bringing an old ColecoVision back from the dead. It was a flea-bay purchase and had a dead power supply, faulty video memory, a dodgy power switch and a broken cartridge connector!. Anyways, I have replaced the memory - now 5V only, repaired the power switch, replaced the cartridge connector and it now runs OK from a 5V power supply with a 5V to 12V (Pololu U3V50ALV) up converter inside the case. The problem I now have is that I am getting vertical lines on the sprites as shown in the attachments. Its fine when the games startup in text mode but appears as soon as a sprite is present. I have attached some photos of the problem. Can anyone help and point me in the direction of the problem please? Thanks very much for your help.
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