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Cbm 2001 Pet strange boot

For a start you haven't set CH 2 volts/division to the same as CH 1 have you?

I am not seeing any evidence of UD2 being faulty so far...

Dave
 
Now you have changed the Volts/division setting, the oscilloscope doesn't appear to be synching onto the wave anymore.

You now need to adjust the timebase trigger LEVEL control to get as stable a signal on CH 1 as you can.

Dave
 
Maybe for me is more easy to unsold jumber block or replace Ud2 :(
I am desperate now.... :(

 
I am really confused about what I am seeing on the video without any frame of reference.

Let's forget the oscilloscope for now.

Before you warm up the soldering iron again ( :) ), Hugo mentioned something else back in post #1,304 FIRST...

Dave
 
Hugo Holden said:
And some IC's did use a Tin plated pin, so every pin of the IC's connected to the pin 9 connection need to be inspected for a whisker and pass a tool between the pins, for example pin 1 and pin 2 A4 and pin 11 & pin 10 & 12 of A3, just in case there is a whisker connecting to an adjacent pin on those IC's. (Unlikely it would have been around pin 9 of U2 as soldering there would have destroyed it)
Click to expand...
Checked but not continuity with multimeter between pins indicated!
 
Just replace UD2 when your part comes in.

If it works it works; if it doesn't - you'll get desperate again and we will have to start over with the oscilloscope...

However, I can see how this fault potentially affects the screen - but not why you weren't getting any pulses on the /CS pin of the PETTESTER ROM. You may have another fault after this one...

Dave
 
daver2 said:
Just replace UD2 when your part comes in.

If it works it works; if it doesn't - you'll get desperate again and we will have to start over with the oscilloscope...

Dave
Click to expand...
Can i try to unsold jumber block maybe or not?
 
if there was a short circuit under the block, I would also see it externally with the tester, right?
 
Desperado,

Daver2 is correct in that it is better to find the exact leakage pathway with the scope, then determine the cause for that.

Are you familiar with Tin Whiskers, have you seen them before ? if not you won't know how to identify them. If you haven't seen them before, look them up on Google images. They can be extremely fine and very difficult to see without very bright light and magnification. They are very fragile and easily broken with the slightest touch.

If there is one causing conductivity to adjacent pins in the switch block area, or between IC pins on the pin 9 connections (the ones I mentioned), then in theory you should be able to see with the scope, with channel 1 locked to pin 9 signal, and one of the adjacent IC pins or adjacent pins on the switch block, using the scope's ch2, that the signals match up.

Obviously if there is no direct short (or conductive pathway) to any of the connections and track-work to pin 9, then it has to be a defective 74154 IC.

I mentioned previously how you could have resolved this question by just disconnecting the 74154 IC's pin 9 only and seeing if the output voltage on that pin returned to normal. If it did, then you could conclude there is definite leakage to the track-work going on and it is not the IC at fault. As I mentioned before, one way to disconnect an IC pin (without damage) is to just solder suck that pin. It does require a good solder sucker and it pays to apply fresh solder first. By moving the pin around in the hole it is often possible to get the pin to disconnect from the pad & hole, which you would check with a meter to confirm it was disconnected. Then gently put the scope back onto pin 9 to see if the problem has gone.
 
Ok Hugo, tomorrow i'll try to unsold ud2 pin 9 and check with the scope! ThankS!
 
Hugo Holden said:
I mentioned previously how you could have resolved this question by just disconnecting the 74154 IC's pin 9 only and seeing if the output voltage on that pin returned to normal. If it did, then you could conclude there is definite leakage to the track-work going on and it is not the IC at fault. As I mentioned before, one way to disconnect an IC pin (without damage) is to just solder suck that pin. It does require a good solder sucker and it pays to apply fresh solder first. By moving the pin around in the hole it is often possible to get the pin to disconnect from the pad & hole, which you would check with a meter to confirm it was disconnected. Then gently put the scope back onto pin 9 to see if the problem has gone.
Click to expand...
Hugo i am desperate really now!!
I disconnected ud2 pin 9 from board and i tested this pin with scope and now signal is good!!! :(
 
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