pavery
Experienced Member
Wa-hoo! Solved it!
Wa-hoo! Solved it!
Good news team - found the problem. Ye haa!!! :D
It was the *other* PIO in the Kaypro - the SYSPIO (U72). This generates the BANK signal which has to go Hi to enable the Boot ROM. This BANK (A) [A means this signal goes to schematic sheet 'A'] signal was stuck low and didn't pulse on Reset. At that moment I knew I had the smoking gun. So I pulled that PIO just to observe the signal & low & behold - a boot screen appeared! EPROM was fine after all - just wasn't being enabled. Yet, observing the /CE on the EPROM with a probe showed it was active for a burst at Reset, but this must have been a side effect of Reset. I interpreted that as ok, but now I see /CE is enabled (pulsing) *the whole time* while the "Insert Disk" screen is displayed. Renewing *that* PIO got the disk to boot up to "A>" prompt.
Now what about that suspect Z80 CPU? Sure enough, when it was put back in - screen flashed garbage, no boot. So it was *two* big i/cs that failed - PIO & CPU. Nasty, because the symptom (screen flashing garbage, no boot) was the same for either one of the failures. Come to think of it thou - this symptom is typical in 8 bit micros that won't boot & can mean a multitude of causes.
I will write up a full blog to go on Tezza's site, when I get my head around more of this. I will include some Troubleshooting Tips that will assist future Kaypro fixers regarding no-boot scenarios.
Thanks team - we got there in the end.
Philip
Wa-hoo! Solved it!
Good news team - found the problem. Ye haa!!! :D
It was the *other* PIO in the Kaypro - the SYSPIO (U72). This generates the BANK signal which has to go Hi to enable the Boot ROM. This BANK (A) [A means this signal goes to schematic sheet 'A'] signal was stuck low and didn't pulse on Reset. At that moment I knew I had the smoking gun. So I pulled that PIO just to observe the signal & low & behold - a boot screen appeared! EPROM was fine after all - just wasn't being enabled. Yet, observing the /CE on the EPROM with a probe showed it was active for a burst at Reset, but this must have been a side effect of Reset. I interpreted that as ok, but now I see /CE is enabled (pulsing) *the whole time* while the "Insert Disk" screen is displayed. Renewing *that* PIO got the disk to boot up to "A>" prompt.
Now what about that suspect Z80 CPU? Sure enough, when it was put back in - screen flashed garbage, no boot. So it was *two* big i/cs that failed - PIO & CPU. Nasty, because the symptom (screen flashing garbage, no boot) was the same for either one of the failures. Come to think of it thou - this symptom is typical in 8 bit micros that won't boot & can mean a multitude of causes.
I will write up a full blog to go on Tezza's site, when I get my head around more of this. I will include some Troubleshooting Tips that will assist future Kaypro fixers regarding no-boot scenarios.
Thanks team - we got there in the end.
Philip
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