Cbm 2001 Pet strange boot

[Desperado]

With a BLANK EPROM installed. We are NOT changing the configuration unless I tell you.

Remember that we don't change the configuration?

The BLANK EPROM should be producing the VOLTAGE that we should be measuring on the data bus.

Dave

Ok but need i insert cpu on socket or nop?

 

[Desperado]

in this moment i removed the wires from cpu socket for continuity test...

 

[daver2]

The wires that you had installed before - no CPU, no NOP.

Why did you need to remove the wires to perform the continuity test? There should have been nothing connected to the CPU data bus.

Dave

 

[Desperado]

Why did you need to remove the wires to perform the continuity test?

I wanted to remove them to avoid possible contact during the test..

 

[Desperado]

Can you use your logic probe and check the data levels on each pin of UD9 and post back the results please.

UD9 PINS:

1 TO 8: LOW
9 TO 11: NO SIGNAL
12: LOW
13 TO 17: NO SIGNAL
18 TO 20: LOW
21 HIGH
22 TO 23: LOW
24: HIGH

 

[Desperado]

Can you also measure the DC voltage (using a digital multimeter) at the actual UD9 ROM itself (black lead to pin 12 and red lead to pin 24)

5,1 V

Can you also measure the DC voltage on the /CS line (using a digital multimeter) at the actual UD9 ROM itself (black lead to pin 12 and red lead to pin 20).

102 mV

Then double-check (with the logic probe) the logic levels on the CPU socket pins 33, 32, 31, 30, 29, 28, 27 and 26 again.

maybe I found the problem during this measurement, I inserted a piece of rigid cable in the socket to measure the status with the probe ... I noticed that for example in pin 26 I have no signal but if I move the cable left and right then I see the signal pulsate. Could this white cpu socket be faulty?

 

[daver2]

We are still working on UD9... Forget the CPU socket for now...

The address and control lines on UD9 appear to be correct (address lines all LOW, chip select line LOW and a correct voltage supply) but it would appear that the EPROM is not outputting any data onto the data bus (UD9 pins 9-11 and 13-17 NO SIGNAL).

So, back to basics, what type of EPROM have you programmed and got fitted in UD9? If you put this EPROM back into your EPROM programmer and read it - do you get all FF's? Is the EPROM installed the correct way round within UD9?

Are you measuring the signals with your logic probe directly on the pins of the EPROM plugged into UD9?

Dave

 

[Desperado]

what type of EPROM have you programmed and got fitted in UD9?

Tms2532JL

Is the EPROM installed the correct way round within UD9?

yes!

Are you measuring the signals with your logic probe directly on the pins of the EPROM plugged into UD9?

Yes directly on the pins

 

[Desperado]

do you get all FF's? Is the EPROM installed the correct way round within UD9?

yes i see all FF's!

 

[daver2]

Well, that all sounds correct - so why isn't it working then?

There are very few pins that you need to connect on an EPROM (in this configuration) to get it to work...

You need 0V/GND on pin 12 (power).

You need +5V on pins 24 and 21 (power).

You need a LOW signal on pin 20 (active low chip select).

Since we have programmed all FF's into the EPROM - it doesn't really matter what the input address lines actually are - but I have specified all LOW so the first memory cell is selected. Ultimately, if we get this test to work, we will put the Abracadabra ROM back in and select specific addresses to double-check the correct data is coming out but (at the moment) this is not relevant.

With the power and chip select being correct - the EPROM should be outputting data. The only reason why your logic probe is saying NO SIGNAL would be if we have bus contention - and that is what we were trying to look for with the last test with the oscilloscope - but failed dismally.

Can you double-check the the UD9 data bus pins with your logic probe (pins 9-11 and 13-17) and also read the DC voltage on each of the pins. The logic probe will tell is if it still thinks there is NO SIGNAL and the DC voltmeter reading should confirm this.

Report back and I will have a look to see where the contention could be coming from. The only thing I can think of would be the data bus buffers from the video RAM. But (before you even think about replacing them) we need to confirm this.

Dave

 

[daver2]

Just double-checking - the two PIAs and the VIA are not plugged in are they?

Dave

 

[Desperado]

Just double-checking - the two PIAs and the VIA are not plugged in are they?

yes not PIAs and not VIA on board!

 

[Desperado]

UD9:

9: NO SIGNAL 1,4V
10: NO SIGNAL 1,4V
11: NO SIGNAL 1,4V
13 TO 17: NO SIGNAL 1,4V

 

[daver2]

So, your logic probe and multimeter agree. 1.4V is 'no signal'. For a valid logic '0' you require < 0.8V for a logic '1' you require > 2.0V. Devices should OUTPUT < 0.4V or > 2.7V.

Either your EPROM is not performing correctly (i.e. it is dead) or something else is driving the data bus at the same time. With the PIA and VIA devices out of circuit it can't be them. The only other devices could be E9/E10.

Can you use your logic probe and check the signals on pins 1 and 19 of both E9 and E10 please.

Dave

 

[Desperado]

E9:

1: L
19: H

E10:

1: L
19: H

 

[daver2]

They are correct...

So, what we are left with is either ROM UD9 is not working, the buffers E9 and E10 are faulty - or there is something fundamentally wrong with the known Laws of the Universe.

What other pre-programmed ROMs do you have that you could put into UD9?

Dave

 

[Desperado]

What other pre-programmed ROMs do you have that you could put into UD9?

Abracadabra and original rom

 

[Desperado]

the buffers E9 and E10 are faulty

E9 is in socket but E10 is soldered on board

 

[daver2]

Put the original ROM into UD9 then and repeat the entire pin testing (using the logic probe) for all 24 pins of UD9 ROM and post the results.

Dave

 

[Desperado]

UD9 ORIGINAL ROM:

PIN 1 TO 10: L
11: H
12 and 13: L
14: H
15 : L
16: H
17 TO 20: L
21: H
22 and 23: L
24: H