My Hitachi CP1421R smoked

[agardiner]

It is unlikely that the replacement IC has failed. They normally 'blow up' when they go like your original one did. Far more likely that there is still something else wrong. You need to check all the peripheral components in the primary of the supply.

[Foneet1]

Originally Posted by Welsh Anorak

All your measurements should be in DC mode.
The most likely items to have died will be D806, D808 and R804.

Yep, R804 is dead. It is burned too, but the mark is on the bottom where I couldn't see it. Diodes seem to be ok, despite the torture me and my poor soldering skills have put them through.

[Foneet1]

Aand no effect

Except now the IC values are 315 on pin 1 and 0 on all others.

[Foneet1]

Also, maybe it's just my meter but the resistors are supposed to be 0.56 ohm and it's showing 0.8 ohm.

The first one I soldered in had flaked a bit and no longer shows anything on the meter, second seems to be ok.

[Foneet1]

And another thing I noticed is that on schematic R804 is a circled zigzag, unlike the other ones. In the part list it's listed as a "fusible", and the one I put in instead is a metal film resistor. Could that be the problem?

I read about it, and it seems that a "fusible" resistor is just a fuse and a resistor in 1, so I guess it isn't a problem?

I swear, if this is some kind of "left the lens cap on" issue... maybe I shorted the IC or something? because my hand did slip a few times.

[John123]

Fusible resistors are often marked as 'safety-critical', so it's good practice to replace like-for-like.

Check any more that you find on the schematic, as it's not always immediately obvious if they have gone open-circuit without going through and testing each one. Also look on the schematic for anything marked as 'ICP' or 'circuit protector'.

[hans]

Originally Posted by Foneet1

Aand no effect

Except now the IC values are 315 on pin 1 and 0 on all others.

Is R803 ok? This resistor supplies voltage to pin 9 which is the power supply to all the "logic" in the IC.

[Foneet1]

Originally Posted by hans

Is R803 ok?

Yes it is. But it's showing 67.5k Ohm instead of 68k.

[marceljack]

Originally Posted by Foneet1

Yes it is. But it's showing 67.5k Ohm instead of 68k.

It's largely within the tolerance (generally +/- 5%), I would say it's almost perfect !

[Welsh Anorak]

Without any voltage on pin 9 the IC won't do anything. So we need to look at where this voltage has gone.
You've checked the feed resistor, so check there's a high voltage at one end and zero at the other. This means it's being loaded down.
Coud be the new IC (unlikely) or a diode connected to it which isn't in your diagram. Check for a low ohms reading from pin 9 to earth (Tv off and main capacitor discharged, of course). If you have one then find out what's loading it down.

Make sure all diodes have an infinite resistance on your meter's ohms range. Under 1M won't do!

Why not get an electric desoldering tool? They aren't expensive and will save you a lot of trouble.

Also if you say your soldering isn't the best, check you haven't damaged a track by looking under a magnifying glass with good lighting.

[Foneet1]

Originally Posted by Welsh Anorak

Check for a low ohms reading from pin 9 to earth.

Make sure all diodes have an infinte resistance on your meter's ohms range. Under 1M won't do!

It says 2.9k ohms, and everything between that caps negative leg and pin 9 is working fine.

All the diodes have around 2M Ohms.

[Foneet1]

So now I've checked everything in the power supply, and everything is working.

It could be another cap losing its juice, I can't measure capacitance, so I can't see if they are working badly. Though in that case I think there would be some signs of life.

It could also be the IC, or some other component.

Or some broken/burnt traces. I haven't seen any though, and I always checked if connections are still there. Wouldn't hurt to test one more time, right?

[Foneet1]

The second R804 resistor also flaked and stopped working. Even though the TV wasn't plugged in and caps were discharged.

[Foneet1]

Also I can't find this resistor anywhere. I need a 2W 0.56 Ohm fusible resistor, please help.

[agardiner]

The exact value is not too critical; the fusible element is quite important. If it were me, I would try putting a 1.5 ohm fusible and 1 ohm 0.75W fusible in parallel. These are easy to get values from the likes of Cricklewood.

[Foneet1]

Originally Posted by agardiner

a 1.5 ohm fusible and 1 ohm 0.75W

What about the watts though? Would that be ok? And just to make sure, they both have to be fusible and 0.75W?

[agardiner]

2 0.75W resistors in parallel will equate to 1.5W, which should be OK in this position. And yes, both would need to be fusible resistors though.

[Foneet1]

Originally Posted by Foneet1

The second R804 resistor also flaked and stopped working.

I see, but what does this mean? The normal resistors I put in there are burning out. Is it because they aren't fusible?

[agardiner]

A fusible resistor is just a special kind of resistor designed to go open circuit in a controlled, quick manner. Basically a resistor that doubles up as a fuse. Most are very low values.

If you are fitting an ordinary resistor as a replacement and it is burning up, then you have another fault which needs investigating.

[Foneet1]

Originally Posted by agardiner

If you are fitting an ordinary resistor as a replacement and it is burning up, then you have another fault which needs investigating.

Could that be an old capacitor? I don't have a capacitance tester, so I can't tell.