Need to repair this (commercial product) multiple 9V distribution stripe

[arma61]

Hi there

I've been given this to fix, no 9V at the output, what I get is 15V from the, separate, wallwart up to the diode, then after the 60 XF050  (PTC Overcurrent Protection Device??) I only get 3 to 4 volt and the PTC is becoming very hot.





At first I though the PTC is damaged, but now I'm thinking that, for a reason or another, also the 7809 may be damaged and over doing something that gets the PTC hot.

What do you think ? I have 7809s on hand but no PTC, what value should I look for, if I need to change the PTC ?


Thanks, as usual, for your help!!

Ciao
Armando

[R.G.]

It is extremely likely that the PTC is doing what it's supposed to do - open up when too much current is being pulled. I suspect that one (or more!) of the output regulator circuits are drawing so much current that the PTC is opening up.

It's also possible that either the PTC is damaged, or that the wrong PTC was put in in an earlier repair attempt.

[arma61]

Thx RG for reply!

there is only one regulator at the beginning, for the hole stripe, so, at the end could be that the 7809 is gone?

Thx

[PRR]

You have a short downstream of the PTC.

Start cutting traces until the PTC bops back up to 9V.

[arma61]

thx Paul

unfortunately it's not mine so cannot cut traces 

What happend to this board, according to the owner, if felt down and been "walked on" so the input socket got loose and the + wire disconnected. Wire is now connected to the right tab and socket is working properly.
Could the shock have damaged the 7809 ?

What I've done till now
Checked the hole board, no previous repair present, as far as I can see.
Checked all traces all good, no breaks.
Checked all the 4 sockets, there's no shorts.
Checked continuity between gnd and +, no continuity

I have some ideas, just need "green light" before to make more problem than the present one 

- disconnect the IN leg of the 7809 and check if I get the right voltages at the end of the PTC and it stays cold

- bypass momentarily the PTC and check if the 7809 is working regulating 15 to 9V

what do you think about ?

is there any danger for the board?

Thanks m8s

[Ronan]

You mentioned you have 7809 on hand, why not replace it. It's a very simple circuit, and the chances the 7809 is damaged are good, since there is no short circuit protection.

Edit - while you have it out, check there's no short circuit on its output.

[arma61]

my bad!!! didn't check carefully the big cap there!!!

look




I started to cut one pin of the 7809, PTC hot, then removed it completely, PTC hot, then the next component was that big fart cap... had a look at it... hmmm looks almost like domed......cut one leg, PTC cold, cut the other leg PTC cold, soldered in a new one, even big and farty.. .. soldered a new 7809, bump 9.01v at all the socket.... and PTC cold.

Thanks for your time and help m8s, at least I've learned (almost  ) what a PTC is.


Ciao