They are also very sensitive to faults in the voltage supply in one or more rails, so by running the board with rails out of spec, OP is already risking new ICs giving up the ghost. While other options do indeed exist, the vast majority of issues affecting TR4 or TR5 or faulty 7805s are due to issues in the low RAM bank. You repeat the process until you spot the faulty chip(s). 0 to 300V,500V,600V Measurement, Size : 96 x 96mm AM-V-3 Pointer - Knife Edge Pointer Pointer Deflection - 0 to 90 degree Scale Characteristics - Non Linear Scale Measuring Voltage Range - 0 to 300V,500V,600V Accuracy - Class 1.5 Frequency. If you get voltages back to normal levels, then the fault is in the leftmost half bank, otherwise it is located in the rightmost half bank. In a way, if the 5V rail is below spec due to an overcurrent, it kind of makes. What you would do next is restore the tracks, and cut again disabling half the low RAM bank, four RAM ICs to the left. The speccy generates the 12V and -5V voltages from the 5V output in the 7805.
If the voltages levels are back to normal, then you know the low RAM bank is at fault. You should be more worried if your reported voltages were all 12.00 and 5.50 3.30 right on the dot 100 of the time lol. On the speccies, it is very easy to disable the low RAM bank by simply snipping the three rails to the right of the rightmost 4116. 3 increase or decrease is perfectly normal and stable. The 4116s are definitely known to run hot when shorted, so it is definitely a good idea to check. Yes, the two other voltages are definitely generated from the 5V rail, through TR4, TR5, coil, a few diodes.
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