I got my Time Machine out of storage after moving house, and remembered why it wasn't going

No 5v. Pretty well all the caps have been replaced, as has the Bridge Rectifier.

I have been through and tested for continuity and all looks good and tests fine on the bench.

When I remove all the load from the 5v circuit, I get 5 volts at the test points. As soon as any load goes on (doesn't really matter which board I connect) it drops down to ~half a volt. It is not consistent - sometimes it will be closer to a volt after I have restarted. The 12v is always closer to 14v (and a bit higher when the 5v is down)

Looking at Clays guides, and the circuit diagram it seems the next suspects are the voltage controller chip or the large transistor on the heatsink.

I don't want to just shotgun replace everything, and I'd prefer not to have to replace the IC.

What is the best way to test/diagnose to narrow down the problem ?

What voltages should I see on the other leads of the transistor or inputs/outputs of the IC?

And secondary question, recommended currently available parts to replace the 2N6057 transistor or MC1723CP voltage regulator chip.

Thanks

Thanks for the info.
Pins 11/12 on the 723 show 27V with no load (and 5V at the test point)
With load I have 3.6V at pins 11 and 12 )and 1.3V at the test point.

R6 has the same voltage as the test point and doesn't show any voltage drop between the ends. I had replaced the original resistor and I couldn't get a .12ohm so it is a .1ohm.

The problem goes back to before the machine was in storage, and from memory one of the backbox fuses by the backbox bridges and 30,000uF capacitor had been replaced just before it went into storage.

So I have also tested the AC voltages at the fuses 1 & 2. The voltage at Fuse 1 (coming from pin 10) is very low when the 5V is not working. Reads the same as the voltage at the other fuse when there is no load and 5V test point shows 5V. Does this suggest I need to look at the block connector or even back off the board at where the nominal 9 V AC (reads about 10V) is coming from ?

Thank you G-P-E and ChrisHibler for your help and advice.

Yes, that is where my thinking is going. Fuse holder or even the pin 10 or connector on the CN1 block. I need to take the board out and look at that. When I put some a wire round pin 10 and some pressure on CN1 to create a test point there, the 5v became more stable.

Thanks again ChrisHibler and G-P-E , I think I have the 5V steady now.

One question though - The 34volt DC for the coils reads at 43V. Should I be concerned ?
(I'm in NZ where we are 230V 50Hz, and I have removed the fuse for the 100V circuit because I have an XPin display in the machine).

I *think* it was getting a better connection at Connector 1 for the 9V AC input. I had replaced the pin some time ago. I will keep an eye on it, and rewire the female side if I get problems later.