IBM 6734_HBO: 2sec to black

[Welchs101]

Hi,

A friend brought me an IBM model number 6734_HBO (not ABO).

Background:
I plug in the monitor and it turns on for 2 to 4 seconds then turns off.

I opened it up and found a 1000uf/10V bulging. Replaced cap with a new one 1000uf/25V. Put monitor back together and powered it up. Still the same thing.......2 to 4 seconds on and then off.


What i have done:
1- replaced bulging cap. No change.

2-I checked ALL 4 lamps and they all seem to be ok. I used my home-made bulb checker.

3-Measured voltages at connector (see enclosed pic of connector):
Pin1=>13v when off. When on ~14V and then when shuts down voltage goes to 12.6V
Pin2=>13v when off. When on ~14V and then when shuts down voltage goes to 12.6V
Pin3=>0V
Pin4=>0V
Pin5=>0V
Pin6=>0V
Pin7=>4.96V
Pin8=>0.138V
Pin9=>when off ....0V.........when on....2.72V.

Note: See connector pic.......i dont seem to measure the 3.3V.

Note: When making measurements at the connector i did by accident short pins 4 and 5 just for a second. It does not appear to have done any damage since i still get the same error.......2 to 4 seconds to black.


4-I checked fuse located in the inverter section......seems to be ok.....0.2ohms.

5-I worked on a similar monitor as shown below. But not exactly the same.
https://www.badcaps.net/forum/showthread.php?t=10055


Any ideas on where to start.

[momaka]

Re: IBM 6734_HBO: 2sec to black

If there's one failed/bulged cap, then the rest are probably not far behind. I see that you have CapXon caps in your unit. Replace them all (except the 400v one) - it's common for CapXon to go bad in LCDs.

As for the 3.3v rail - can't say why it's not there. If you can get a picture that covers the whole underside of the PCB, that would be helpful.

[retiredcaps]

Re: IBM 6734_HBO: 2sec to black

Agreed. I find it a bit hard to trace the 3.3v rail without a whole underside picture.

If that one cap was bloated, you might want to check IC660 to see if it is okay since it is close proximity?

As for the 3.3v rail - can't say why it's not there. If you can get a picture that covers the whole underside of the PCB, that would be helpful.

[Welchs101]

Re: IBM 6734_HBO: 2sec to black

I am enclosing an "overall" pic of the back of the power-supply/inverter board.

I also measured the IC660:
Note: MEasurements same with either black or red lead first/second.
Pin1 to Pin2: Measured resistance was 9.9kOhm
Pin1 to Pin3: Measured resistance was 0.4ohm
Pin2 to Pin3: Measured resistance was 9.9kOhm

[alexanna]

Re: IBM 6734_HBO: 2sec to black

I am unsure of your 3.3v problem either .But it sounds like you may be going into the current protection mode. I know you most likely checked it but is there a picture that you can see with flash light?
Have you tried with three of your lcd lamps hooked up,Install a known good lamp into one of the connectors and then repeating down the line to see if you can see any difference?
Al.

[Welchs101]

Re: IBM 6734_HBO: 2sec to black

When the lamps go out i can still see a faint picture. However, I did not look at this to make sure that the picture stays on for a long time. I just happened to notice that when the lamps went out i could still see a picture.

I checked all the lamps using a home made lamp tester.

[alexanna]

Re: IBM 6734_HBO: 2sec to black

Ok you know your bulbs are good.What I am suggesting checking the circutry of each of the ccfl connectors.I have found it is very hard to see whats happing thru the dark lcd.Try hooking your known good bulb up to each connector,See if it lights.If for only A second?
Al.

[Welchs101]

Re: IBM 6734_HBO: 2sec to black

I guess i dont understand. How is connecting a known good bulb doing anything if i have already verified the bulbs are "good". Sorry but i dont understand.

[alexanna]

Re: IBM 6734_HBO: 2sec to black

My mind and my fingers dont work very good together some times.In the other ibm thread you had made a test jig to test each circut on your inverter did you try that on this monitor?
Al.

[retiredcaps]

Re: IBM 6734_HBO: 2sec to black

Odd, I can't see how pin 5 and 6 (if it is 3.3V as marked on the board) go anywhere on the back side?

What is IC660? That is, what is written on it?

I am enclosing an "overall" pic of the back of the power-supply/inverter board.

I also measured the IC660:
Note: MEasurements same with either black or red lead first/second.
Pin1 to Pin2: Measured resistance was 9.9kOhm
Pin1 to Pin3: Measured resistance was 0.4ohm
Pin2 to Pin3: Measured resistance was 9.9kOhm

[PlainBill]

Re: IBM 6734_HBO: 2sec to black

I guess i dont understand. How is connecting a known good bulb doing anything if i have already verified the bulbs are "good". Sorry but i dont understand.

A common inverter design has one 'stability' feature, as well as two forms of protection. The stability feature feeds the total CCFL current back to the inverter controller so the lamps are running at their designed current.

The two safety features react to the maximum current through any one lamp and the maximum voltage across any lamp. By substituting a known good lamp in turn for each original lamp you can determine if the problem is caused by a lamp that is drawing too much current (current draw increases as the lamp ages).

If you remember the IBM monitor I helped you with a few weeks ago, try the same test I PM'd you'.

PlainBill

[Welchs101]

Re: IBM 6734_HBO: 2sec to black

ok. I shorted pin 3 and pin 20 of the BIT3105. In the previous monitor you helped me with the monitor stayed on after doing this (not a permanent fix) but for THIS monitor lamps went out....ie....no change. Monitor comes on for a few seconds then goes off.

[momaka]

Re: IBM 6734_HBO: 2sec to black

Have you tried changing all of the caps yet? If not, at least change the 25v, 220uF CapXon next to F1 and maybe another cap on the 5v rail. I'm still very suspicious of the rest of the CapXon caps.

Odd, I can't see how pin 5 and 6 (if it is 3.3V as marked on the board) go anywhere on the back side?

Yeah, it seems the 3.3v was omitted from the PSU design, so pins 5 and 6 may be ignored when doing measurements again. I'm guessing the video board probably has it's own 3.3v regulator.

[Welchs101]

Re: IBM 6734_HBO: 2sec to black

momaka,

I have not changed all the caps. I was hoping i would not have to go this route. I did borrow a friends ESR meter and i measured the ESR values of the caps (in circuit) ......they seem ok.

[PlainBill]

Re: IBM 6734_HBO: 2sec to black

ok. In the previous monitor you helped me with the monitor stayed on after doing this (not a permanent fix) but for THIS monitor lamps went out....ie....no change. Monitor comes on for a few seconds then goes off.

OK, that means it's not an sensing an open lamp, so that side can be ignored. Now try measuring the resistances of each transformer secondary. I've circled the pins.

PlainBill

[Welchs101]

Re: IBM 6734_HBO: 2sec to black

Measured transformer:

Note measurement on transformer #3:
Transformer1: 0.981Kohm
Transformer2: 0.975Kohm
Transformer3: 5.0Kohm
Transformer4: 0.997Kohm

Question:
These transformers........what am i measuring? I know conceptually what a transformer is supposed to do and how its supposed to look. But the transformers on these inverters always have more leads than simple "input side" and "output side". The points you mentioned in the picture.......what am i measuring?

[PlainBill]

Re: IBM 6734_HBO: 2sec to black

Measured transformer:

Note measurement on transformer #3:
Transformer1: 0.981Kohm
Transformer2: 0.975Kohm
Transformer3: 5.0Kohm
Transformer4: 0.997Kohm

Question:
These transformers........what am i measuring? I know conceptually what a transformer is supposed to do and how its supposed to look. But the transformers on these inverters always have more leads than simple "input side" and "output side". The points you mentioned in the picture.......what am i measuring?

You are confusing physical configuration with electrical configuration. Recall, on a schematic a capacitor is always shown with the two leads opposite one another - even a radial cap. This transformer design has one end of the secondary attached to the same end of the transformer as the primary windings. And you are measuring the resistance of the secondary - the high voltage winding.

Fortunately, replacement transformers are available - just search for 8TT00006.

PlainBill

[Welchs101]

Re: IBM 6734_HBO: 2sec to black

So based on the measurement values #3 transformer is bad...........right?

I looked up this transformer......only found one site "lcdparts.com" that sells it. Do you know of another place?

Also, any ideas where i can find a datasheet on this thing. Just wondering how you knew that i was measuring the "secondary" resistance.

Thanks!

[retiredcaps]

Re: IBM 6734_HBO: 2sec to black

So based on the measurement values #3 transformer is bad...........right?

Also, any ideas where i can find a datasheet on this thing. Just wondering how you knew that i was measuring the "secondary" resistance.

It should be around 950ohms according to this

http://www.lcdparts.net/TransformerD...ProductID=3355

The picture in the above URL shows you the pins for primary and secondary.

This is just like that video on how to test transformers

http://www.youtube.com/watch?v=eNuGWBPRGKA

[el3ctroded]

Re: IBM 6734_HBO: 2sec to black

Just wondering how you knew that i was measuring the "secondary" resistance.

One reason is because of the resistance. The primary has low resistance, whereas the secondary has a higher resistance. If you had one pin of each, you would get nothing, unless the coils had shorted, but then all pins would read connected to all the others (that assumes there's only 1 secondary)