| Electronics > Repair |
| ADVANTEST R9211B |
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| m k:
It's guessing then. Left of CPU is quartet of chips. LS164 serial to parallel is interesting, but probably not for this case. HC148 is 8to3 lines priority encoder, its likely buddy is old style LS07 OC driver. If so then HC148 output pins 9,7 and 6 can be connected to LS07 input(A) pins and output(Y) pins to CPU IPL pins 25, 24 and 23. Since LS07 style is open collector there must be pull-up resistors. I remember that those IPL pins have been up in some picture, but I'm not sure. Faulty resistor network is not uncommon either. Open collector here can mean that some other direction is also connected to those CPU pins, but all of them must be also open collector style and near by gates are clearly totem-pole style. It's also possible that some controller chips have open collector interrupt lines, so they can connect directly. |
| stfjohn:
From what I can see from the copper side of the PCB, the connections would be as follows: CPU pin 25 connected to HC148 pin 9. CPU pin 24 connected to HC148 pin 10. |
| m k:
Is pin 9 a corner pin? CPU _HALT(17) and _RESET(18) are bidirectional, so good destinations for open collector drivers. If so then input side of the pair can be shorted and go to *SOFTRST output of a timer chip. (just something for possible future use) |
| stfjohn:
Yes: corner pin. |
| m k:
Pin 10 is input 0, so it's coming from somewhere else also. DMAC _IRQ pin is 21, is it connected there? KBC _IRQ is pin 4, is it connected to some other input of HC148? |
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