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Cbm dual drive 3040 disk - two red lights

Desperado said:
With the logic probe on cpu pin 40,i have always low signal when i turn on...also on pin 7 :(
Click to expand...

Ah, so the 6502 CPU is permanently held in a RESET condition - that will not do it any good for working will it?!

So, where does this signal come from on the schematic? A bit of homework for you... Sorry, going to make you work...

Dave
 
Correct.

So use your logic probe on the output of UL2 (pin 12) and then move your logic probe back to the input of the gate (at UL2 pin 13).

Then check the output from the dreaded 555 timer (UM2 pin 3).

Report back the results. Let's see if we can track down the reason for the permanent RESET signal.

By the way, the 555 reset circuit is the same as a PET (so the same description as @Hugo Holden gave still applies). There is, however, a slight 'twist' to it that we will get to presently (if we need to).

Dave
 
daver2 said:
Correct.

So use your logic probe on the output of UL2 (pin 12) and then move your logic probe back to the input of the gate (at UL2 pin 13).

Then check the output from the dreaded 555 timer (UM2 pin 3).

Report back the results. Let's see if we can track down the reason for the permanent RESET signal.

By the way, the 555 reset circuit is the same as a PET (so the same description as @Hugo Holden gave still applies). There is, however, a slight 'twist' to it that we will get to presently (if we need to).

Dave
Click to expand...
I have always low signal on UL2 pin12 and 13 and on UM2 pin 3 :(
 
A LOW on UM2 pin 3 and UL2 pin 13 is correct.

A LOW on UL2 pin 12 is not correct. UL2 is an inverter - so the output should be the logical inverse of the input (but it isn't).

So, you either have a device on the output of UL2 pin 12 pulling the line LOW, UL2 is dead or UL2 doesn't have a power supply.

I would suggest measuring the voltage on UL2 (using a multimeter) between pins 7 and 14 of UL2 (pin 7 = black lead, pin 14 = red lead). You should read approximately +5V.

The other thing to do would be to measure the signal on UL2 pin 13 whilst you short out C19 temporarily. This should give you a reset pulse on UL2 pin 13.

Do the same whilst monitoring UL2 pin 12 (whilst you short out C19 temporarily) and see if you get a pulse...

If not, UL2 could be a candidate fault.

Dave
 
daver2 said:
Suggerirei di misurare la tensione su UL2 (usando un multimetro) tra i pin 7 e 14 di UL2 (pin 7 = cavo nero, pin 14 = cavo rosso). Dovresti leggere circa +5V.
Click to expand...
yes i have 4,95V
daver2 said:
The other thing to do would be to measure the signal on UL2 pin 13 whilst you short out C19 temporarily. This should give you a reset pulse on UL2 pin 13.
Click to expand...
i can see for an istant a yellow led on logic probe but i have always low signal (green led).
Same for pin 12
 
I can actually understand the Italian translation!

4.95V is good.

I am not so sure about the next measurement though. Can I suggest wiring a normally open pushbutton across C19. Pressing the button will then force a reset condition. This is exactly the same as we would do for a manual reset on a PET computer.

Then, put your logic probe on the measurement point, press (and hold) the pushbutton, take a logic reading, then release the pushbutton and observe how long it takes for the measurement point to change state. Measure UL2 pin 13 first and note what happens and then measure UL2 pin 12 next.

Dave
 
I have a working 4040. I have just tested it and can confirm that the three LEDs flash on at power on and then go off in all of the following scenarios:

1) PET switched on
2) PET powered off, but cable connected
3) PET powered off and cable disconnected

I have the manual that covers the 3040 and 4040 and it does not highlight any difference in the LEDs between the 3040 and the 4040.

If some/all of the LEDs never power off, there may be a deeper problem here. If it is simply that the central Power LED never turns on, it may just be the LED has blown - I had to replace one of them myself.

Hope this helps.

Colin.
 
All - I am happy to do some comparative voltage/scope testing here although I do have a 3016 and a 4040 so I'm not really sure how comparative it will be. I'm guessing the IEEE port and supporting ICs didn't change much between the 2001 and the 3016?

I also have covid so I have plenty of time....although limited energy.

Colin.
 
ScottishColin said:
I have a working 4040. I have just tested it and can confirm that the three LEDs flash on at power on and then go off in all of the following scenarios:

1) PET switched on
2) PET powered off, but cable connected
3) PET powered off and cable disconnected

I have the manual that covers the 3040 and 4040 and it does not highlight any difference in the LEDs between the 3040 and the 4040.

If some/all of the LEDs never power off, there may be a deeper problem here. If it is simply that the central Power LED never turns on, it may just be the LED has blown - I had to replace one of them myself.

Hope this helps.

Colin.
Click to expand...
Thanks!! Can i test central led with a transformer maybe?
 
OK - then I think you have a different problem to a blown LED, but we will need help from others to work that through.

In the meantime you can test the central LED by opening up the case, tracing back the wiring for the central LED and plugging in a new LED to the sockets that the central LED is plugged into.

At the next power on, this should show if the LED is at fault or not. Makes sure the =ve and -ve legs of the LED are plugged into the correct location.

There are probably more elegant solutions to this, but this is what I did.

Colin.
 
daver2 said:
Measure UL2 pin 13
Click to expand...
if i press and hold on button, i can't see nothing on logic probe ( not pulses, no low and no high), if i release button i have low signal.
On UL2 pin 12 i have low signal in both situations!
 
ScottishColin said:
In the meantime you can test the central LED by opening up the case, tracing back the wiring for the central LED and plugging in a new LED to the sockets that the central LED is plugged into.
Click to expand...
you were right, the central led works ... someone had connected the plug backwards!
Now also the central red led is always on
 
This could point to bad Rom or RIOT chip. Have you re-seated the IC’s ? Also do the drives spin up at all ?
 
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