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Cbm dual drive 3040 disk - two red lights

Desperado said:
I have 4,6 V on UM2 pin 3 with button pressed!
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This is a logic HIGH - so why does your logic probe state that it is indeterminate?

If you release the button, does the voltage fall immediately, or does it take a short while before it falls to 0V?

Dave
 
daver2 said:
This is a logic HIGH - so why does your logic probe state that it is indeterminate?

If you release the button, does the voltage fall immediately, or does it take a short while before it falls to 0V?

Dave
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Dave i'm desperate!! Why i can't see high signal with my logic probe??? :(
 
daver2 said:
If you put the probe on UL2 pin 14 (+5V) does it indicate HIGH? If not, your logic probe is probably faulty.
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On UL2 pin 14 i can't see any signal with logic probe :(
Maybe bad power supply for logic probe??
 
Desperado said:
On UL2 pin 14 i can't see any signal with logic probe :(
Maybe bad power supply for logic probe??
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Just out of interest, what supply is powering the logic probe? Where is it taken from?

I would next test out the logic probe on a piece of equipment that I know is working...

There is nothing worse than trying to use test equipment that is faulty.

Dave
 
Ah, there you go.

Desperado, the logic probe should ALWAYS be run from the same supply voltage as the chips you are faultfinding on. These are +5V powered chips, therefore the logic probe should be running from +5V as well. Try Dave's tests again, but with the probe running from +5V, not +12V.
 
SiriusHardware said:
Desperado, the logic probe should ALWAYS be run from the same supply voltage as the chips you are faultfinding on. These are 5V - powered chips, therefore the logic probe should be running from +5V as well. Try Dave's tests again, but with the probe running from +5V, not +12V.
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Sorry but i am a big donkey :(
you're right Sirius!
I tried with logic probe on 5V and now i have correct reset signal on cpu pin 40....low and after high :(
 
Excellent...

Always good to know how to use the diagnostic tools.

I thought something was a bit amiss when I read your post.

Now we know we are getting a RESET, you can check pin 7 of the 6502 CPU (UN1) again to see if there are SYNC pulses.

Dave
 
daver2 said:
Just out of interest, what supply is powering the logic probe? Where is it taken from?

I would next test out the logic probe on a piece of equipment that I know is working...

There is nothing worse than trying to use test equipment that is faulty.

Dave
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Sorry but I did not know that it was powered only at 5v ... I read in the manual that it could be powered by 5 to 20V
 
Now i see that central led it switches off two seconds after switching on but the other two remain on and fixed!
 
Desperado said:
Sorry but I did not know that it was powered only at 5v ... I read in the manual that it could be powered by 5 to 20V
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If you read the manual you may find something stating that LOW is 30% of VCC and HIGH is 70% of VCC.

Bear in mind that VCC (in this case) is the supply that you are powering the logic probe from...

TTL runs from 5V, but CMOS can be up to 15V/18V etc. You have to connect the logic probe power supply to the same supply as the devices you are probing.

Dave
 
So, the 6502 CPU (UN1) is either not executing instructions - or failed soon after the RESET.

The LED flashing is driven by software. If the CPU is not executing instructions - it can't do anything.

Is the 6502 CPU (UN1) soldered in or in a socket?

Monitor the 6502 SYNC pin and apply a manual RESET to see if there are any signs of activity on SYNC at all. It will be brief...

Dave
 
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