Excellent video. Wish I'd seen this before I fixed my 4032 12" monitor board. I ended up verifying all of the waveforms from the service manual and changing all the electrolytic caps before finally finding the R752/R753 resistors. If I ever repair one again that's the first thing I'll try!
Really nice repair video Chuck. I'm sure Dave will be very happy to have his PET video boards back and to get his machines up and running. I'm a huge fan of the PET computer. I recently moved my PET 2001-N into my main computer room so it's now getting daily use.
There is debate about that. A lot of people prefer to hear the snap so they know when the discharge happened (or not). With a resistor, there's some guessing required for how long to hold it to be sure you've bled off the full charge.
These resistors are fusible resistors, (thats also why they are mounted away from the board using the mounting pin). So changing them for normal ones with even higher watt rating is not the best idea.
I've never seen that mentioned before. Afaik the parts list just shows them as normal metal film resistors. I assumed the standoffs are mainly for heat dissipation, but I could be wrong. Why would a fusible resistor need that standoff? I'll have another look at the schematics and parts list. Thanks.
I can't actually find a parts list for this version of the board but I re-checked the schematic and it only specifies RN type resistors. I also reviewed some old online postings as well and found no mention that these should be fusible. The only 56 ohm fusible resistor I could find online now is rated for 2 watts.
What caused the cascading failure? Replacing the diode and cap, followed by resistors seemed related to another issue. If the diode has failed, do you suggest replacing all at once? Diode - cap - resistors?
Thanks for putting this info online! My PET 12" 4032 had a burned out resistor in the CRT.
Excellent video. Wish I'd seen this before I fixed my 4032 12" monitor board. I ended up verifying all of the waveforms from the service manual and changing all the electrolytic caps before finally finding the R752/R753 resistors. If I ever repair one again that's the first thing I'll try!
Really nice repair video Chuck. I'm sure Dave will be very happy to have his PET video boards back and to get his machines up and running. I'm a huge fan of the PET computer. I recently moved my PET 2001-N into my main computer room so it's now getting daily use.
That is nuts! You can an also replace those small film caps with new tiny TDK box caps.
8:45 I even jumped when I heard that lol.
Again at 13:48 lol. I don't think I will get over the fear of high voltage.
It would be interesting to measure the voltage drop across those two resistors, to determine the actual operating current/wattage.
Great repairs! Really enjoying your channel! Thanks for sharing
Thanks 👍
Neat set of fixes. Why not put a resistor into your bleeder circuit to avoid the snap?
There is debate about that. A lot of people prefer to hear the snap so they know when the discharge happened (or not). With a resistor, there's some guessing required for how long to hold it to be sure you've bled off the full charge.
Good point. Maybe there is DIY tool to be made to bridge the gap! Thanks for the video!@@HutchCA
\o/ Jameco!
These resistors are fusible resistors, (thats also why they are mounted away from the board using the mounting pin). So changing them for normal ones with even higher watt rating is not the best idea.
I've never seen that mentioned before. Afaik the parts list just shows them as normal metal film resistors.
I assumed the standoffs are mainly for heat dissipation, but I could be wrong. Why would a fusible resistor need that standoff?
I'll have another look at the schematics and parts list. Thanks.
I can't actually find a parts list for this version of the board but I re-checked the schematic and it only specifies RN type resistors.
I also reviewed some old online postings as well and found no mention that these should be fusible.
The only 56 ohm fusible resistor I could find online now is rated for 2 watts.
What caused the cascading failure?
Replacing the diode and cap, followed by resistors seemed related to another issue.
If the diode has failed, do you suggest replacing all at once? Diode - cap - resistors?
I'm pretty sure the bad cap caused the diode failure. The resistor failure is unrelated and quite common on these boards.