IBM L200p - 6736-HC9 - powering off and on

[ank]

Ok here is my first attempt to repair, or rather save from the recycle bin, a good monitor. Please do not shoot. I have a degree in electronics/computer interfacing but actually never used that knowledge (30 yeard old now) having gone into systems administration. Out of necessity not choice. SO I can understand muh of the theory but have very limited practical tech abilities.

This particular monitor, IBM L200p 6736-HC9, has been in service for around 8 years but is in good condition except that after powering on and working properly it suddenly looses power, front led goes off. Several minutes later it just comes back on may stay for a few seconds to minutes on and then powers off again. This continues ad nauseum. I have noticed that sometimes after about 20-30minutes it will really decide to stay on, but not always.

This is what I have done up to now:
1) I went through the thread https://www.badcaps.net/forum /showthread.php?t=35158&highlight=6736-HC9 which was very informative to me and tried to follow on some suggestions there.
2) Visually checked all capacitors, no problem detected.
3) I have traced my AC (220V 50Hz) on switch, fuse etc and seems ok.
4) Voltage on big caps is more than 400V (is this right?)
5) I tried several components, rectifies, regulator etc and did not find anything wrong. May be grossly wrong.

Got stuck!
Any suggestions? Thanks all.

[stj]

Re: IBM L200p - 6736-HC9 - powering off and on

you wont find the bad part here.

solder some wires on the psu outputs so you can leave a voltmeter connected to it while it's in use.
see if the psu is actually still running when it looks dead.

that will narrow it down between the psu and control board.

and post some good foto's of the psu - i suspect i know what's wrong - but i'm not playing the guessing game because it could waste money.

[ank]

Re: IBM L200p - 6736-HC9 - powering off and on

OK, coming back to this. Thanks for the reply. I had a hard time getting voltages during failure. The thing just would not fail. Eventually it started acting up again and I managed to get the following voltages on the power connector to the logic board. I give first the label on the board then the voltage during normal operation and then during failure.

12/18v, 18, 10
12/18v, 18, 10
GRD, 0, 0
GRD, 0, 0
5v, 4.8, .05
5v, 4.8, .05
GRD multimeter probe
5v, 4.8, .05
N/F, 3.2, 0
VBL, 3.2, 0
NC, 0, 0

I am attaching a photo of the power supply board. The connector is seen at the lower right corner with the probe cables barely visible.
Thanks for any help

[stj]

Re: IBM L200p - 6736-HC9 - powering off and on

well 2 things stand out.

1 - the voltages are a bit low.
so it probably has some bad caps.
i'd replace the 2 small ones bottom-center next to the heatsink - because some idiot put them near a heatsink!
and maybe change the ones on the lower-right too.

there is a u-shape heatsink center-right, if some satanic devil worshipper put caps under it - change them.

the second thing that stands out is that it didnt want to go wrong after you opened it.
this may indicate some bad soldering that got moved.

check the soldering on the connectors, the transformers, and anything bolted to a heatsink.


it looks like it works btw, but it's just going into standby mode.
so that's the mystery to solve - and low voltages may be the cause.

if not, it's going to be time to look at the invertor & tubes.

[budm]

Re: IBM L200p - 6736-HC9 - powering off and on

"5v, 4.8, .05
5v, 4.8, .05"

Since it is an always on power supply, for the 5V to drop to 0.05V that means it stops running for reason. As suggested by STI, check for bad solder joints, bad caps, etc. The 5V should always be there if even when the monitor is in standby mode because it is an always on supply, there will be 12V (or 18V as marked on the board depend on the board setup) and 5V the minute you apply the AC to power the board.