Hello there,

I'm trying to diagnose a startup (I think) problem on my 6 year old Daewoo
2898ST CRT, with the aim of repairing it myself (as I can't afford to
replace or have it repaired at the moment). I used to tinker with
electronics a long time ago and I'm aware of the dangers and precautions
needed when working inside TVs and monitors.

Service manual here;
http://www.eserviceinfo.com/download...oo_2594ST.html

The set was working fine then made 2 popping sounds and went off, It didn't
blow any fuses when it went off. It now makes a constant ticking noise from
the psu area.

If it was a HOT failure would you expect it to have taken out a fuse?
I get no voltage across the collector / emitter of the HOT, do I have to
remove the HOT to check it for shorts or can I do it in situ and what should
I be looking for?

Or is this a power supply problem and how / what should I start to test?
I'm currently reading this smps troubleshooting guide;
http://www.repairfaq.org/sam/smpsfaq.htm#smpsmcp
but I'd appreciate any and all help in pointing me in the right direction.

Thank you,

Ian

"Ian" wrote in message
...

The set was working fine then made 2 popping sounds and went off, It
didn't blow any fuses when it went off. It now makes a constant ticking
noise from the psu area.

Shorted somewhere?

"Homer J Simpson" wrote in message
news:Yz1Ig.19110$tP4.10180@clgrps12...

"Ian" wrote in message
...

The set was working fine then made 2 popping sounds and went off, It
didn't blow any fuses when it went off. It now makes a constant ticking
noise from the psu area.

Shorted somewhere?


Thanks Homer,


The HOT checks out as shorted when in situ, I then removed it and it still
shows only an ohm or so across B-C, B-E and C-E in both directions, I take
it this means it's dead?

Are there any specific components I should look at that may have failed and
caused the HOT to go or anything that may have failed due to the HOT
failing?

Before I removed the HOT I checked to see if there was ~132v between the C
and E and there was no voltage present between any of the three pins, is
this just a symptom of the HOT failure - power supply not coming up /
regulating?

I've found three fusable resistors that all check out ok, a 60w bulb in
series with the mains lead glowed bright with the HOT in place and still
glows bright with the HOT removed. Does this mean that there is still a
short somewhere and where should I look?

Any and all help appreciated.

Ian

"Ian" wrote in message
...

The HOT checks out as shorted when in situ, I then removed it and it still
shows only an ohm or so across B-C, B-E and C-E in both directions, I take
it this means it's dead?

I'd say so but I haven't done this stuff for 30 years.

Before I removed the HOT I checked to see if there was ~132v between the C
and E and there was no voltage present between any of the three pins, is
this just a symptom of the HOT failure - power supply not coming up /
regulating?

the power supply is trying to come up but since the hot is shorted it is
shutting down due to overcurrent protection
does the b+ (voltage at the collector of the hot) come up to around 130v
with the hot removed?

I've found three fusable resistors that all check out ok, a 60w bulb in
series with the mains lead glowed bright with the HOT in place and still
glows bright with the HOT removed. Does this mean that there is still a
short somewhere and where should I look?

does the bulb dim after a while - this could just be the degauss circuit it
takes a while to switch off with a series bulb

check the high voltage rating capacitors around the area of the hot and
flyback for incorrect capacitance opens or shorts (out of circuit) also
check for arcing at the flyback or around the connections to the yoke -
these things can blow the hot or sometimes it just gets tired!

Any and all help appreciated.

Ian

no probs

"Neilish" wrote in message
...

Before I removed the HOT I checked to see if there was ~132v between the
C and E and there was no voltage present between any of the three pins,
is this just a symptom of the HOT failure - power supply not coming up /
regulating?

the power supply is trying to come up but since the hot is shorted it is
shutting down due to overcurrent protection
does the b+ (voltage at the collector of the hot) come up to around 130v
with the hot removed?


Yes B+ at the collector is okay with HOT removed.

I've found three fusable resistors that all check out ok, a 60w bulb in
series with the mains lead glowed bright with the HOT in place and still
glows bright with the HOT removed. Does this mean that there is still a
short somewhere and where should I look?

does the bulb dim after a while - this could just be the degauss circuit
it takes a while to switch off with a series bulb


The bulb dims after a few minutes with the HOT removed, but did not dim with
it in. I'm only using a 60w bulb at the moment, from what I've read I
should be testing with a ~150w bulb for a 28" CRT with the HOT replaced, is
this right?

check the high voltage rating capacitors around the area of the hot and
flyback for incorrect capacitance opens or shorts (out of circuit) also
check for arcing at the flyback or around the connections to the yoke -
these things can blow the hot or sometimes it just gets tired!

I've ordered a replacement HOT, which should be here Tue/Wed, and I'll start
checking the components around the HOT in the meantime. Is it safe to
assume that the LOPT is okay as there were no blown fuses.

Thank you for the reply,

--
Ian