First thing is to replace all Tantalum capacitors
They can often short circuit and burn so this is my top priority.
As can be seen on the pictures a lot of mainly blue tantalum capacitors are found. Also other colors.
I will not use tantalum again. I did consider to use capacitors with low ESR like ceramic X7R types but the pcb layout is from a time where tracks are longer than today and EMC was not an issue, especially with slow IC’s like used in ABC 80. So the tantals will be replaced by standard electrolytic capacitors. Todays technologies Offers much lower ESR than 47 years ago. There are still a lot of ceramic capacitors near the IC’s so this should work.
Values of 2u2 and 47uF and 150uF was found on 5V and 17V rails sobi will choose 25 V types.
Thermal photos
I have now replaced all the tantals with standard electrolytic capacitors and powered up the CPU board with 5V and +/- 17 V lab power supply. The current at 5V is approx 2,5 A wich I need to investigate as this is too high.
Here are some thermal photos
In the upper picture you see the 4 x ROM’s and 2 x video RAM
In the picture below the PROMS are approx 60 C warm. They consume 140mA each, approx 1 Watt per. PROM.