After warm up running with short/overcurrent

[kataklysm]

Hi everyone.
My frend was give me a zx spectrums, one with case and second only pcb (its junk for parts)

After few days i was fix one of this (issue 4A)

What was replaced:
Tr4
Tr5
All electrolytic capacitors
Some diodes like d9,d13
One of ram chips (this one was be warmer than others when i used thermovision)
+5v regulator

After this zx run correctly again, passed ram test, buzzer working, games loading and run without any problems but...

I using regulated power supply "korad" default with short protection, when i play some time, eg 20 minuts and power off the Spectrum after this i cant run it again because short protection are kick out psu. I must wait few minuts, when temp fall i can run this again.

I think its may be a temp protection in regulator because i dont have radiator in this one but before i replaced all capacitors this situation has occured randomly on cold machine too.

So, maybe someone can help me? I dont have any ideas what to do

[1024MAK]

If you are using a conventional voltage regulator like a 7805, it does need a suitable heatsink fitted. Otherwise it will overheat. When it overheats it will reduce the output voltage causing malfunctions.

A ZX Spectrum 16k/48k/+ with no expansions fitted, typically requires between 600mA and 700mA. The input voltage from a regulated supply can be between +7.5V and 11.9V. If using an unregulated DC supply, the recommended on load voltage should be between 8V and 11.5V (the off load voltage should be less than 13V).

If the above does not answer your question, or you still have difficulty, please let us know.

Mark