TT/Mega STE power supply headaches

[damanloox]

I've been trying to find the issue that I have with my TT (or PSU specifically)... Long story short (exxos knows the details as I have been bothering him on Sunday ;)):
My TT seems to have a long delay when powered for the 1st time (after longer period of being idle/powered down and by longer I mean about 10-15 minutes) - when powered up the PSU seems to start, has all correct voltages except "power good" signal (orange wire). It takes about 20-30 seconds and PG magically goes to 5v and... TT starts (and works) perfectly OK. So the big question is - what can cause such delay...? Does anybody know what generates "PG" ("power good") signal (on orange wire)? Is it PSU or TT?
And another question - I can see R4 has been removed from my PSU and R5 is about 50 Ohms (instead of 100 Ohms as per PSU diagram)... Does anybody have any idea if that could be the issue...?

NOTE: the "delay" issue is non-existent when I use good PSU from another machine.

[exxos]

It takes about 20-30 seconds and PG magically goes to 5v and... TT starts (and works) perfectly OK. So the big question is - what can cause such delay...? Does anybody know what generates "PG" ("power good") signal (on orange wire)? Is it PSU or TT?

PG circulates around C23.. if you put 220uF instead of 22uF then it could take 10x longer to power up (30-60 seconds maybe). I put 10uF there I think in my kit, so about 2 seconds is normal.

And another question - I can see R4 has been removed from my PSU and R5 is about 50 Ohms (instead of 100 Ohms as per PSU diagram)... Does anybody have any idea if that could be the issue...?

Its factory calibration, its normal, even says in PSU docs I think.

NOTE: the "delay" issue is non-existent when I use good PSU from another machine.

1-3 seconds delay is normal, so depends what your classing as normal here ? if it powers up in under a second, then PSU may be malfunctioning and may need re-capping. "no delay" doesn't mean PSU is good.

[damanloox]

PG circulates around C23.. if you put 220uF instead of 22uF then it could take 10x longer to power up (30-60 seconds maybe). I put 10uF there I think in my kit, so about 2 seconds is normal.

I'll check the cap tomorrow... I hope I made mistake and installed wrong cap... That would finally allow me to enjoy my new TT...

1-3 seconds delay is normal, so depends what your classing as normal here ? if it powers up in under a second, then PSU may be malfunctioning and may need re-capping. "no delay" doesn't mean PSU is good.

I meant on the "good" PSU delay is about 1-2 seconds...

[exxos]

I'll check the cap tomorrow... I hope I made mistake and installed wrong cap... That would finally allow me to enjoy my new TT...

Also check you not put it in backwards...

A guess also on values, is that is 10uF gives 2 seconds, then 100uF 20 seconds.. 200uF 40 seconds..

I meant on the "good" PSU delay is about 1-2 seconds...

Yes, that should be fine. Powering up 1 second or less is getting onto sticky ground for the HV side to ramp up and start switching.

[damanloox]

Double checked C23 and it is 10uF as per exxos replacement/upgrade. So no joy... I double checked all caps in fact and they are all as per recap kit...
I'm stuck again... Any other ideas...? I'm so desperate I may go ahead and replace all components of PG part of the circuit (just need to find equivalents)

[exxos]

Check you have 5V and 12V input to the 2 transistors ?

[stephen_usher]

Yes, that should be fine. Powering up 1 second or less is getting onto sticky ground for the HV side to ramp up and start switching.

That's interesting as my TT always powered up in less than a second from brand new. It was *click* (about half a second) wurrr.

[exxos]

That's interesting as my TT always powered up in less than a second from brand new. It was *click* (about half a second) wurrr.

Be interesting if you could change C8 for a newer capacitor and see what the startup time is then. The one I had took about 4 seconds to turn on, its why I lowered the value from 22uF to 10uF to turn on faster (2 seconds). So don't know why some do and some dont. Either different revisions or very bad tolerances of multiple parts. :shrug:

[damanloox]

Check you have 5V and 12V input to the 2 transistors ?

OK, here's what I measured right after power up (ie. when voltages reach their correct values but PG is still not OK)
Q2: Vce = 1.1V, Vbe = 0.5v
Q3: Vce = 0.7v, Vbe = 0.6V
Q4: Vce = 0v, Vbe = 0.7v

Any ideas..?

[exxos]

Do you get 5V and 12 V on one side of R29,R31,R33..

On collector of Q2, turn on and see if the voltage changes over time.. try over 60 seconds...