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Commodore PET CBM 4016 ASSY 8032080 RIFA burn and more

Sorry for the delay. I had to redo my measurements due to a mistake. here are my measurements. I put high / low on the schematic inside the red and the more interesting signals pictures of osci.
 

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I will follow up on UE5 and UD2. Generally, assuming the PET worked some months before and most likely failure is 4116 failure. What video signal do we get with dram / rom issue / failure to boot? also just 5v / high? if yes then tracing back from video signal is likely not the fastest route, correct?
 
There should be no CRTC controller on this board.

Can you just double check that.

If this is true, even if I pull the CPU, ROM and RAM out - I should still get a random character video screen!

The video 'picture' has absolutely NOTHING to do with the 6116 DRAM, or the OR or the CPU.

Dave
 
There was one unusual finding that you got an ultra-bright dot in the screen center on the VDU. Unless you were non specific and this only appeared, for a while, after the VDU was turned off.

The reason is that in this VDU (assuming the schematic we have applies to your VDU) it uses a frame Sync pulse and a horizontal Drive pulse (though they label that H sync on the schematic, it is not).

If the H drive pulse goes missing, there is no H scan and no EHT (black screen). If the V sync goes missing the raster scan would still be there, just out of vertical lock, if the H drive was ok.

To get a bright dot continuously with the VDU powered, it would require the H drive pulse was present to generate EHT , but both the H scan and V scan currents were absent from the CRT's yoke, suggesting that the deflection yoke was disconnected. So it may be worth checking the connections to the deflection yoke, if they are on a plugged connector, there could be fractured solder joints on the pcb pins.
 
I have no idea what the pictures of the oscilloscope are actually indicating to me...

UD4/13 is permanently LOW - it shouldn't be. This takes us back to UC1/5 and the associated pins.

Hugo (good morning) that is what I previously suggested - to look at the soldering etc. for the scan coil plug/socket arrangement.

Dave
 
daver2 said:
I have no idea what the pictures of the oscilloscope are actually indicating to me...

UD4/13 is permanently LOW - it shouldn't be. This takes us back to UC1/5 and the associated pins.

Hugo (good morning) that is what I previously suggested - to look at the soldering etc. for the scan coil plug/socket arrangement.

Dave
Click to expand...
Good morning to you too, but I am about to head back to bed, it is 3.30am here !
 
Ah yes.

Change of schematic - change of circuit!

So, stuffed RAM or ROM means a potential black screen.

This is where my PETTESTER pays for itself. My PETTESTER only cares for a handful of instructions in the Kernel ROM working and no RAM.

So I see you have two (2) of the dreaded white sockets...

In this case, HDRIVE and VDRIVE directly come out of the CRTC (pins 39 and 40) respectively.

Dave
 
ah ok ... yeah had this hunch that black isn't necessarily video circuit. ok so i ll make my pettester search post now...
 
Also it is a 4016 and you did mention some adjustments needed for your rom in that case.

also, is there a way to scope out defective ram?
 
DrAlis said:
and more white sockets hiding underneath cpu and edit rom
Click to expand...
They were the important ones I was pointing out - the other two are irrelevant because there is nothing plugged into them...

If there is a bad connection to the CPU or EDIT ROM - your machine will not function correctly.

Unlikely to scope out faulty RAM if you do not know what is in there to start with I am afraid.

If you look in the source code for the PETTESTER there are different tables for programming the CRTC. The correct table values need to be copied into the EPROM programmer before programming the EPROM.

Dave
 
what is the issue with the white guys? do the legs break off? or do they make bad contact? i pulled both put and back in already... cpu was very tough
 
also for the thermally interested i have two thermal images of no-image pets for you to enjoy or maybe have some detective insights
 

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i do find UE6 and UE7 to be hot in the left PET (this POST) and considerably less in the right PET (alternate broken PET)... They are the ICs two the right of the (gold cap) edit rom. one day, i will find a justification for that thermal cam...
 
We should be on the same schematic we were on at post #42 where you drew the red border.

Post #58 doesn't seem to be the correct schematic...

Didn't I say look at UC5/1 in post #46?

What are you measuring UB2/11 for?

I am confused.

OK, stop what you are doing please and download ALL of the correct schematics for your specific PCB before we start doing anything else - or we are just going to get ourselves hopelessly lost.

Dave
 
Well I am at least as confused. Which ones are my schematics? I have Assy 8032080 as per title... Please let me know which of Zimmers are the right ones. Thanks
 
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