Hello everybody!
First of all please forgive me for my not so well English, it is not my first language. So...
Before two days i got my precious Commodore PET 2001-32N BS. Till now i never had the chance not even see one in real and finally i got one! I take it faulty with horizontal lines on the screen. Photo is from others member thread cause today i take apart the monitor from the case, but i have the same issue.
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What i find so far is that i missing -5V on ram IC's. I check the voltage regulator and i have output 0v. The input is -10V. One of my questions that i dont want to forget to ask, is that on schematic i see that pet 2001 use 7905 regulator. In my case my motherboard have 7906 regulator. Is that normal?
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What i did after i saw the missing -5V, is to test the HM4716A-4 Ram's with my arduino tester one by one. Luckily all Ic's are in working order. So, i just clean very well the IC legs and put them away till i fix first the issue with the regulator.
Photo 5-12-19, 12 48 17-min.jpg Photo 5-12-19, 13 25 19-min.jpg Photo 5-12-19, 13 25 23-min.jpg Photo 5-12-19, 13 26 15-min.jpg Photo 5-12-19, 14 47 01-min.jpg
What other things i found in the board are some "mods" that may be tell something to you.
First there is a cut on trace that going at UG6 74LS107 Pin12.
Photo 5-12-19, 10 15 52-min.jpg Photo 5-12-19, 10 33 56-min.jpg
Also, there is a bypass cable that connect the previous UG6 74LS107 Pin12 with the UH6 74LS107 Pin2.
Photo 5-12-19, 10 33 13-min.jpg Photo 5-12-19, 10 16 12-min.jpg
Finally, the is one more cut on the trace that normally connect the UH1 74S74 pin12 with UF1 74LS08 pin3.
Photo 5-12-19, 10 16 22-min.jpg Photo 5-12-19, 10 33 22-min.jpg
All this i can tell for now. The reason i take apart the monitor from the case in because i read that is very risky to do test's with the original monitor. I am waiting the schematic from here http://www.vcfed.org/forum/showthrea...230#post597230 to connect an external monitor to the motherboard.
Should i replace the faulty voltage regulator? But with what, 7905 or 7906? And check after the replace the -5v if they come back on board.
I have a voltmeter and i just buy a logic probe, eprom programmer, mini oscilloscope (in the way), in case i need them for the repair.
Thank you all very much for your time reading all this and i really cross my fingers for your help!![]()
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