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| IIc strange image |
Posted by: WillJac on 2022-07-17 11:16:30
Can I see the schematic? You need to trace pin 4, the WE pin, it's got some issues in the write enable circuitry This for the 16 chip ram logic board A2S4000. I have the A2S4100 that schematic is VERY bad quality and is on page 407-411 of this attached manual. I decided send the entire manual as it could help you. |
Posted by: WillJac on 2022-07-17 11:39:13
The signal starts at the TMG chip as 01 pin 14 good solid signal nice form. Goes to R59 then to the 74LS32 pin 4 comes out on pin 6 and is garbage. See the pics. Going in, out and last is at pin 4 on the ram. Seems everything coming out of this 74LS32 is bad garbage. |
Posted by: Lycus on 2022-07-17 11:42:26
The signal starts at the TMG chip as 01 pin 14 good solid signal nice form. Goes to R59 then to the 74LS32 pin 4 comes out on pin 6 and is garbage. See the pics. Going in, out and last is at pin 4 on the ram. Seems everything coming out of this 74LS32 is bad garbage. Awesome, that's exactly what I was looking for, I'd replace that 74LS32. |
Posted by: WillJac on 2022-07-17 12:01:32
Awesome, that's exactly what I was looking for, I'd replace that 74LS32. I hope it’s this but I made a error. This pics and results are with ROM and CPU removed. Does it make different? I can redo with them in socket. |
Posted by: Lycus on 2022-07-17 12:06:40
I hope it’s this but I made a error. This pics and results are with ROM and CPU removed. Does it make different? I can redo with them in socket. You need all chips in their sockets. This would be potentially caused by the CPU R/W line not being there so it's just floating. |
Posted by: Lycus on 2022-07-17 12:11:12
I hope it’s this but I made a error. This pics and results are with ROM and CPU removed. Does it make different? I can redo with them in socket. If those readings are from with all chips installed, then I'd say for sure that 74LS needs to be replaced. |
Posted by: WillJac on 2022-07-17 12:18:15
The first set of pics are with cpu and rom the last set I send were with them out. I will do with them in. |
Posted by: WillJac on 2022-07-17 12:25:09
Ok here is a full set pin 14 on TMG, one side of resistor, other side resistor, pin 4 in on 74LS32, exit on pin 6, pin 4 ram 1, pin 4 ram 2, pin 4 ram 3, pin 4 ram 4. |
Posted by: Lycus on 2022-07-17 12:30:41
The last five are kinda funky to very funky. I'd probably replace that 74ls |
Posted by: WillJac on 2022-07-17 12:55:47
The last five are kinda funky to very funky. I'd probably replace that 74ls Those 5 from pin 6 on 74LS which is the out pin goes to 4 and ram 1 and 2. Ram 3 and 4 I need check as that comes from another source. That is the Aux memory. |
Posted by: Lycus on 2022-07-17 12:58:10
Those 5 from pin 6 on 74LS which is the out pin goes to 4 and ram 1 and 2. Ram 3 and 4 I need check as that comes from another source. That is the Aux memory. Well no matter what I'd say it needs a replacement. |
Posted by: WillJac on 2022-07-17 12:58:11
i will see where I can borrow a 74LS from to test it. Don’t have any new right now. |
Posted by: Lycus on 2022-07-17 12:58:40
i will see where I can borrow a 74LS from to test it. Don’t have any new right now. Crossing my fingers! |
Posted by: Lycus on 2022-07-17 14:30:29
If you order new ones, this is the exact same chip, just new.
There's also these which are even faster, which won't really do much for you, I don't think it'll make it not work, but it's slightly cheaper. |
Posted by: WillJac on 2022-07-17 15:24:28
I will need to order I don’t have any laying around. I going to see my other machines maybe borrow from them. |
Posted by: WillJac on 2022-07-17 15:40:37
Thanks. I just order some but had to use Amazon as I need it delivered tomorrow as I have a friend coming to visit me Tuesday from Miami. I live overseas in the Cayman Islands so it’s hard for me to get parts. I know is not best quality but it’s what i can do in a pinch. |
Posted by: Lycus on 2022-07-17 15:51:03
Hey, whatever works! As long as it's a 74LS32 it'll work. Let me know if that fixes it, I think that might be it. |
Posted by: WillJac on 2022-07-17 16:23:59
Hey, whatever works! As long as it's a 74LS32 it'll work. Let me know if that fixes it, I think that might be it. Well I open up my other IIc to probe the chips and I get same results. It seems the keyboard needs to be connected to get the proper signal on pin 4. I will send you some pics shortly. Outside with the kids a bit before they disown me. |
Posted by: Lycus on 2022-07-17 16:33:10
Strange, reprobe with the keyboard connected then |
Posted by: WillJac on 2022-07-17 17:02:11
Here are the pics for current machine with issues. In order pic 1 is pin 6 on 74ls32. Pic 2 is pin 4 RW on chip 1, pic 3 is chip 2.
Pic 4,5,6 same pins different machine that is working. |
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