I have iMac that I have been trying to repair.

The orginal fault was that the unit would not power up. Put a fuse in
and it would pop. Checked and found that the transistor SSF9N80A was
shorted on all legs. Replaced it with a BUZ355 which is the closest I
could find without having to specially import the transistor.

Anyway when I powered it up next, I found that (what it looks like) the
posistor has blown and spat all over the case. I suspect it is a
posistor as it runs in series with the fuse and is close to the degauss
coil. It is actually soldered on a set of pins exactly like the ones you
would normally plug the degauss coil.

Anyway normally I understand you can just leave the posistor out, but
since this is running in series with the fuse, without it, the rest of
the unti will not power up.

Is there anyway I can bypass it (just link the gap?, or link with with a
fuse?) so I can be sure it was this that was causing the fault in the
first place?

The markings on the part:

15D15 with the letters T and P

Maybe it isn't even a posistor.....if not what is it?

Thanks

TEX

"TEX" wrote in message ...

| Anyway when I powered it up next, I found that (what it looks like) the
| posistor has blown and spat all over the case. I suspect it is a
| posistor as it runs in series with the fuse and is close to the degauss
| coil. It is actually soldered on a set of pins exactly like the ones you
| would normally plug the degauss coil.
|
| Anyway normally I understand you can just leave the posistor out, but
| since this is running in series with the fuse, without it, the rest of
| the unti will not power up.
|
| Is there anyway I can bypass it (just link the gap?, or link with with a
| fuse?) so I can be sure it was this that was causing the fault in the
| first place?

If it is a posistor and is in series with the degauss coil, bypassing it
will leave the coil running continuously. This is NOT a good thing. You
could replace it with a push button temporarily.

N

I have had another look and there is a proper posistor (black box with
three legs), this thing I am having probs identifying looks like a large
disc ceramic capacitor. Black in color. Has the markings 15D15. Runs
inline with the fuse.

Thanks

TEX


TEX wrote:

I have iMac that I have been trying to repair.

The orginal fault was that the unit would not power up. Put a fuse in
and it would pop. Checked and found that the transistor SSF9N80A was
shorted on all legs. Replaced it with a BUZ355 which is the closest I
could find without having to specially import the transistor.

Anyway when I powered it up next, I found that (what it looks like) the
posistor has blown and spat all over the case. I suspect it is a
posistor as it runs in series with the fuse and is close to the degauss
coil. It is actually soldered on a set of pins exactly like the ones you
would normally plug the degauss coil.

Anyway normally I understand you can just leave the posistor out, but
since this is running in series with the fuse, without it, the rest of
the unti will not power up.

Is there anyway I can bypass it (just link the gap?, or link with with a
fuse?) so I can be sure it was this that was causing the fault in the
first place?

The markings on the part:

15D15 with the letters T and P

Maybe it isn't even a posistor.....if not what is it?

Thanks

TEX

"NSM" wrote in message news:l%7xd.5811$KO5.4810@clgrps13...

"TEX" wrote in message
...

| Anyway when I powered it up next, I found that (what it looks like) the
| posistor has blown and spat all over the case. I suspect it is a
| posistor as it runs in series with the fuse and is close to the degauss
| coil. It is actually soldered on a set of pins exactly like the ones you
| would normally plug the degauss coil.
|
| Anyway normally I understand you can just leave the posistor out, but
| since this is running in series with the fuse, without it, the rest of
| the unti will not power up.
|
| Is there anyway I can bypass it (just link the gap?, or link with with a
| fuse?) so I can be sure it was this that was causing the fault in the
| first place?

If it is a posistor and is in series with the degauss coil, bypassing it
will leave the coil running continuously. This is NOT a good thing. You
could replace it with a push button temporarily.

N



That won't work, the magnetic field has to drop gradually, a pushbutton will
only severely magnetize the screen.

"TEX" wrote in message ...
| I have had another look and there is a proper posistor (black box with
| three legs), this thing I am having probs identifying looks like a large
| disc ceramic capacitor. Black in color. Has the markings 15D15. Runs
| inline with the fuse.

Inline with the whole set?

N

NSM wrote:

"TEX" wrote in message ...
| I have had another look and there is a proper posistor (black box with
| three legs), this thing I am having probs identifying looks like a large
| disc ceramic capacitor. Black in color. Has the markings 15D15. Runs
| inline with the fuse.

Inline with the whole set?

N


Yeah. it runs in series straight after the main fuse on the live trace.
It looks like it might be a heater or something? It measures 23ohms
across it, even with a chunk missing from it. Any more help??

Thanks

TEX

"TEX" wrote in message ...
| NSM wrote:

| Inline with the whole set?
|
| N
|
|
| Yeah. it runs in series straight after the main fuse on the live trace.
| It looks like it might be a heater or something? It measures 23ohms
| across it, even with a chunk missing from it. Any more help??
|
| Thanks
|
| TEX

Maybe a soft start device? Seems odd, since I assume this has a SMPS.

N

"TEX" wrote in message ...
NSM wrote:

"TEX" wrote in message
...
| I have had another look and there is a proper posistor (black box with
| three legs), this thing I am having probs identifying looks like a
large
| disc ceramic capacitor. Black in color. Has the markings 15D15. Runs
| inline with the fuse.

Inline with the whole set?

N


Yeah. it runs in series straight after the main fuse on the live trace.
It looks like it might be a heater or something? It measures 23ohms
across it, even with a chunk missing from it. Any more help??

Thanks


Sounds like a posistor to limit the inrush current when the mail filter
capacitor charges, the resistance drops as it warms up. They're often used
when the power supply is software controlled to prevent the current spike
from damaging the triac controlling the power.

Thanks for that James. That is what I thought, one posistor for the
degauss (the back box type with the three legs) and one for the software
power on (the disc ceramic looking one with two legs). I have put back
in anyway, but the psu is still doing the same thing....not doing anything.

Gonna have to check if the standby voltages are present, otherwise just
convert the silly thing to a PC ATX power supply and mod it to a new case.

Thanks

TEX


James Sweet wrote:

"TEX" wrote in message ...

NSM wrote:


"TEX" wrote in message

...

| I have had another look and there is a proper posistor (black box with
| three legs), this thing I am having probs identifying looks like a

large

| disc ceramic capacitor. Black in color. Has the markings 15D15. Runs
| inline with the fuse.

Inline with the whole set?

N



Yeah. it runs in series straight after the main fuse on the live trace.
It looks like it might be a heater or something? It measures 23ohms
across it, even with a chunk missing from it. Any more help??

Thanks



Sounds like a posistor to limit the inrush current when the mail filter
capacitor charges, the resistance drops as it warms up. They're often used
when the power supply is software controlled to prevent the current spike
from damaging the triac controlling the power.

On Sun, 19 Dec 2004 17:39:05 +1300, TEX wrote:

I have iMac that I have been trying to repair.

The orginal fault was that the unit would not power up. Put a fuse in
and it would pop. Checked and found that the transistor SSF9N80A was
shorted on all legs. Replaced it with a BUZ355 which is the closest I
could find without having to specially import the transistor.

Anyway when I powered it up next, I found that (what it looks like) the
posistor has blown and spat all over the case. I suspect it is a
posistor as it runs in series with the fuse and is close to the degauss
coil. It is actually soldered on a set of pins exactly like the ones you
would normally plug the degauss coil.

Anyway normally I understand you can just leave the posistor out, but
since this is running in series with the fuse, without it, the rest of
the unti will not power up.

Is there anyway I can bypass it (just link the gap?, or link with with a
fuse?) so I can be sure it was this that was causing the fault in the
first place?

The markings on the part:

15D15 with the letters T and P

Maybe it isn't even a posistor.....if not what is it?

Thanks

TEX
It's the Degauss posistor,always seem to pop,they are only pennies to
buy and any TV shop will have them or close enough to run as the
degauss specs are not critical,don't run without it,buy a couple.

Harry Hotspur wrote:
Anyway when I powered it up next, I found that (what it looks like) the
posistor has blown and spat all over the case. I suspect it is a
posistor as it runs in series with the fuse and is close to the degauss
coil. It is actually soldered on a set of pins exactly like the ones you
would normally plug the degauss coil.
It's the Degauss posistor,always seem to pop,they are only pennies to
buy and any TV shop will have them or close enough to run as the
degauss specs are not critical,don't run without it,buy a couple.

From the description above it sounds more like the NTC resistor that is
in series with the power supply to reduce inrush current.

---
Met vriendelijke groet,

Maarten Bakker.