IBM monitor won't start up - relay keeps tripping

[Scott M]

I found an IBM monitor model 6547-00N (chassis CM-1317). I cannot get the
unit to start up. It has a relay that keeps clicking on-and-off but there is
NO VIDEO. The monitor appearently suffered from a fall but there are no
visible cracks in the PCB. The monitor has a feature that causes it to
de-guass automatically upon power-up and I suspect that the relay that's
going on and off has something to do with the de-guass routine. Has anyone
ever seen such a problem? My next step is to try and locate a schematic for
this monitor so I can check test-point voltages and begin tracing the
relay's power supply.

 

[Jerry G.]

If the relay is clicking, this means that there is something that is either
shorted or opened and the power supply is going to protect mode. To make a
determination of the cause, you should verify that the power supply is not
being shorted out by something that is loading it, or it is not seeing
proper verification of startup.

Since this monitor was dropped there may be some broken conductors on the
circuit board, or something that is damaged that is causing a short or
opened.

There are many details that have to be determined in order to know what the
fault is.

As for the degaussing, many CRT monitors degauss the tube upon startup. I
doubt your problem is related to the degaussing circuit. You can infact
disconnect the degaussing coil while troubleshooting the monitor.

--

Jerry G.
=====


I found an IBM monitor model 6547-00N (chassis CM-1317). I cannot get the
unit to start up. It has a relay that keeps clicking on-and-off but there is
NO VIDEO. The monitor appearently suffered from a fall but there are no
visible cracks in the PCB. The monitor has a feature that causes it to
de-guass automatically upon power-up and I suspect that the relay that's
going on and off has something to do with the de-guass routine. Has anyone
ever seen such a problem? My next step is to try and locate a schematic for
this monitor so I can check test-point voltages and begin tracing the
relay's power supply.

 

[Zeljko]

If You find schematic let me know...please.

But You don't need it. Don't loose time.
Try the "dumb-mode".
Measure resistances between C-E or D-S of all power transistors - bipolar or
FET. Power diodes also.
If You find any short, take it out and measure again. Check other components
around before You replace this shorted trans.
Of course it can be line output transformer - then You will have HOT blows
again and again.
If You find shorted diode in secondary of power supply trafo - take it out
and measure again. If it's OK now, then You have shorted voltage line - some
other component...
Also You can take out the HOT and try to switch monitor on. If it starts
now - check DC voltages - then You have problem in horizontal output - trafo
or something...

There are also many other troubleshooting techniques...but this quick tests
brings success in 30%...if You can reach copper side of PCB!

 

[Scott M]

Thank you both for your feedback. Upon close inspection of the PCB, I didn't
find any broken solder joints. I couldn't find any obvious short or open
circuits either. I did find a FET that has a D-S short. I removed the FET
and testted it off the board and it still showed a short. If I understand
correctly, a FET transistor is similar to the bipolar as a bipolar should
not have any short between E and C. Therefore, this WOULD indicate that the
FET is fried, correct? I do not understand how a fall would cause that to
happen, but if it's bad, I'll replace it.
I've got a few more to test, but all the other transistors and diodes look
OK as far as my DMM readings go. I'm also doing the best I can to trace the
power supply circuit with the schematic (which has been somehwat elusive so
far).

 

[John Gill]

Scott:
I use the diode check position on my DMM to check most transistors
and FETs. Just look for zero or near zero reading to indicate a
shorted device. An FET will give a 500 to 700 mv reading between
the D-S pins one way with meter leads and high readings on all
the other combinations of pins and leads.
Hope this helps...
John

 

[Van Gardner]

You said you "found" a display and it looked like it suffered a "fall"
and now it has a power problem.

When I read this I visualized someone having a display with a power
problem and throwing it (the fall) in a dumpster. Maybe the fall had
nothing to do with the power problem. Last year I found two new
looking Compaq CV535 displays in a dumpster behind a Rent To Buy
store. One had an open 1meg resistor in the screen circuit and the
other had a defective transistor in the red color circuit. They both
are now on my other computer that I use for video editing.

P.S. I don't normally scrounge dumpsters but I was looking for some
cardboard to lay on while doing some plumbing work under my house. It
made my day.

Van Gardner