1994 Sharp 27F-S40 27-inch color CRT set. (curb find)

Symptom: No power.

Cause: Blown AC line fuse. Replaced fuse, popped again.

I've been looking around, and some places suggest it may be a problem with the degauss thermistor? if this is indeed the problem, how would I know where to find the exact replacement?

This is a decent sized TV with an okay feature list, it would be nice to have it working again. Any help is appreciated.:thmbsp:

Check these items:

A. All four bridge rectifier diodes. One or more could be shorted.
B. Horizontal output transistor for a short.
C. Regulator SCR in the power supply for a short
D. Shorted degaussing coil. Rare, but, it does happen.
E. Shorted degaussing thermistor. You can eliminate D and E by taking them out of circuit and seeing if the set will power up.
F. Shorted main filter cap
G. Shorted AC line choke
H. Shorted "across the line" cap.

If the HOT is shorted, resolder the horizontal driver transformer and everything else around the HOT. Also would be a good idea to check/replace and electrolytic caps in the 130V B+ line. If you do all of this and it blows the HOT again, the flyback is likely bad.

Check these items:

A. All four bridge rectifier diodes. One or more could be shorted.
B. Horizontal output transistor for a short.
C. Regulator SCR in the power supply for a short
D. Shorted degaussing coil. Rare, but, it does happen.
E. Shorted degaussing thermistor. You can eliminate D and E by taking them out of circuit and seeing if the set will power up.
F. Shorted main filter cap
G. Shorted AC line choke
H. Shorted "across the line" cap.

If the HOT is shorted, resolder the horizontal driver transformer and everything else around the HOT. Also would be a good idea to check/replace and electrolytic caps in the 130V B+ line. If you do all of this and it blows the HOT again, the flyback is likely bad.
With the coil and thermistor removed, I would just short across their leads where they were removed?

No, leave them out of the circuit. Don't short across the thermistor or the degaussing coil plug or you will blow the fuse. The set will play just fine with these parts out. You just won't have any degaussing action.

When you get it powered up and playing; play it safe and resolder the power relay (the blue thing in the power supply) and the vertical output IC. Also, resolder any power resistors. I've fixed a ton of Sharp sets from this era simply by resoldering these parts.

No, leave them out of the circuit. Don't short across the thermistor or the degaussing coil plug or you will blow the fuse. The set will play just fine with these parts out. You just won't have any degaussing action.

When you get it powered up and playing; play it safe and resolder the power relay (the blue thing in the power supply) and the vertical output IC. Also, resolder any power resistors. I've fixed a ton of Sharp sets from this era simply by resoldering these parts.

Okay, thanks for that info. I'll get on it as soon as time allows.:thmbsp:

I took some photos just to be sure I'm dealing with the right components:

http://www.wolfness.net/up/files/100_3006.jpg (Power relay circled in blue, degauss thermistor circled in red)

http://www.wolfness.net/up/files/100_3007.jpg (Vertical IC circled in yellow)

Am I doing okay so far? :D

From what I can see, you're right on.

You should be able to trace one of the degaussing thermistor terminals to the degaussing coil plug and the relay will likely have four pins. two pins for the coil and two for the contacts and these pins should be identified by coil and contact symbols on the underside of the PC board.

Before you waste a fuse on testing the degaussing components, check the HOT, the bridge rectifier diodes in the front end of the power supply, and the regulator SCR. Those components are far more likely to cause your problem than the degaussing components.

From what I can see, you're right on.

You should be able to trace one of the degaussing thermistor terminals to the degaussing coil plug and the relay will likely have four pins. two pins for the coil and two for the contacts and these pins should be identified by coil and contact symbols on the underside of the PC board.

Before you waste a fuse on testing the degaussing components, check the HOT, the bridge rectifier diodes in the front end of the power supply, and the regulator SCR. Those components are far more likely to cause your problem than the degaussing components.

At the risk of sounding like a newbie, how would I go about actually testing said components? Would I need to remove them from the board?

SCR, what's that stand for?
(really wishing I had a schematic for this model :D)

Thanks for your help. :yes:

Silicon Controlled Rectifier
Use an ohmeter across collector and emitter of the horizontal output. If you see less than 5 or 6 ohms the transistor is shorted. This usually means flyback is gone too. Unsolder (using desoldering braid) the collector and see if you still have a short to be sure. Check both the transistor and the foil pad to ground. I have seen a few shorted flybacks where the transistor stayed good (rare).
If these are good, I agree with the others that a rectifier diode has probably shorted. Check all four.
A good test for shorts on these sets is to place a 75 watt 120 volt incandescent lamp across the fuse terminals and plug in the set. If the lamp remains bright, keep looking. If it goes bright, then dim, after parts are replaced, I usually double it to 150 watts (two parallel bulbs) and turn the set on.
If you hear high voltage, unplug the set and replace the lamps with a fuse and try again. I save a lot of time with this trick.

The jury is currently out on this set, as I may not have the time or space to continue working on it. Two more sets just came in :D (25" Admiral with some weird colors on the screen, tried degaussing it, but they keep coming back, and a 19" Magnavox whose screen goes wonky when the programming is dark)

The Magnavox has a 100 mfd 160 volt electrolytic bad near the large heat sink in the middle rear of the set. Most of the time they tend to swell and vent out of the top. Dark sccenes tend to set off the HV protect and that causes squiqly pictures
Your Admiral may use the 3 lead degauss thermistor (black square with three tabs soldered to the board. These break loose and cause intermittant trouble with purity. If not, look for bad solder around the thermistor if it is a two lead

The Magnavox has a 100 mfd 160 volt electrolytic bad near the large heat sink in the middle rear of the set. Most of the time they tend to swell and vent out of the top. Dark sccenes tend to set off the HV protect and that causes squiqly pictures
Your Admiral may use the 3 lead degauss thermistor (black square with three tabs soldered to the board. These break loose and cause intermittant trouble with purity. If not, look for bad solder around the thermistor if it is a two lead

Thank you very much! I was thinking of making threads for each of these sets. The Maggie also has a problem with the power button--it only seems to turn half of the set off. Pressing the button removes the audio, but there is still a picture!