Desperado
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- Joined
- Nov 25, 2017
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you will not believe it but even changing the cpu I have the same error!Have you tried replacing the CPU ? You never know, it might work... If not we know what it isn't...
you will not believe it but even changing the cpu I have the same error!Have you tried replacing the CPU ? You never know, it might work... If not we know what it isn't...
Ba0= 142Khz and i have waveformI think you ought to put the NOP generator back in and check all of the address and data pins of the UD9 ROM with your oscilloscope.
BA0 should be 250 kHz (if I remember correctly) with each higher address line decreasing in frequency by a factor of 2 (so BA1 will be 250/2 = 125 kHz).
For the data lines, just check that nothing is stuck at a '0' or '1' for the time being or is not an invalid voltage (e.g. in the range from 0.8 Volts to (say) 4.5 Volts).
Dave
That's not good.UD9:
20: HIGH
Bless you for volunteering. I think we are coming to the conclusion that our friend Desperado has not learned enough computer skills to fix this particular PET that has so many problems.I'm thinking about offering a repair service for your board...
I think you ought to put the NOP generator back in and check all of the address and data pins of the UD9 ROM with your oscilloscope.
BA0 should be 250 kHz (if I remember correctly) with each higher address line decreasing in frequency by a factor of 2 (so BA1 will be 250/2 = 125 kHz).
For the data lines, just check that nothing is stuck at a '0' or '1' for the time being or is not an invalid voltage (e.g. in the range from 0.8 Volts to (say) 4.5 Volts).
Dave
You mean UD2 pin 9 right ?Ok i checked with nop inserted and seems to be all fine except for UD9 pin 2....in this case frequency is not stable:
No.. i mean Ud9 pin 2 Hugo.....You mean UD2 pin 9 right ?
With the NOP running:
Do the pulses look ok on pins 23,22,21 & 20 of UD2 ?
I think you also replaced IC A3, but even so , can you check the output of IC A3 pin 10 on the scope, to see if it is an inverted (upside down version) of the pulse on pin 9 UD2
Ok, sorry.No.. i mean Ud9 pin 2 Hugo.....
Ok thanks, this evening i'll check!!Ok, sorry.
So this is buffered address line BA6 which originates from UC3 pin 12, and its input being pin 8, which is connected to the CPU's pin 15 address label AB6 .
Can you check IC UC3 to see if its inputs and its outputs match, for example compare pin 12 and pin 8. According to the post by ScottishColin, you should see on A6; (pin 15) of 3.096Khz with the NOP running (it should be stable).
Also if the connections (pcb track and UD9 socket) between UC3 pin 12 and UD9 pin 2 are ok the recording should be the same on those two pins.
Can you tell us more about the scope recording on your post #1588 and exactly what you did.
The pin 2 UD9 waveform started out low (I assume you had connected the scope up and the power was off to the board ?) then you switched on the pet, and saw those initial what looked like extra signals while the PET was in the process of a reset ? Then the waveform appeared to stabilize on the scope display, but your frequency counter did not get a stable measurement ? Is this what happened ?
Or was your PET already running with the NOP when you connected the scope to UD9 pin 2 and you saw those extra signals initially? If this was the case, does that happen every time you initially connect the scope to UD9 pin 2 ?
Indeed. Back in the early days the machine was almost working. I feel that new faults are being introduced all the time so we probably now have some broken traces and/or shorts added into the mix.We may have to get a fresh baseline and start again.