Color Classic Needs Serious Help

[rickrob]

Thanks, I'll check the horizontal output transistor.

So far all the seconday diodes are OK, caps, resistors, etc... as well. I've been slowly working my through the board

I figured if that FET went, it took the controller IC with it, so I ordered a couple of those, along with the FET.

The IRFBC40 is rated at 6.2A, but the only thing I can't figure out is what that Termistor might be rated at.

There's a bunch of choices for NTC 10 - 3A, 5A, 6A...

 

[rickrob]

It's Alive-- Been running for about an hour now.

Turns out the only problem was that  IRFBC40 FET and the Thermistor. I replaced the TDA4605-2 controller IC as a precaution.

Now, time to recap the LC550 board....

 

[uniserver]

can you go ahead and just say a little more about what you did?

 

[techknight]

he mentioned what he did? replaced the mosfet, thermistor, and driver IC? 

 

[rickrob]

Yes, That's all I had to do, replace those three parts.

When the fuse originally popped, I replaced it and it popped again.

So I started looking for damaged components-- and saw the damaged Thermistor.

I thought those were supposed to protect against high current? Maybe it did and that's why it went up.

Then I checked components for shorts-- Transistors/FETS first, then diodes then caps, then resistors.

I pulled a few caps out of circuit and tested them with a cap tester in my meter when they looked suspect, but all were OK.

I checked just about every component on the board (in circuit), and couldn't find anything else that looked obviously bad. (Shorted)

I replaced that NTC 10 ohm Thermistor with a 3A , from what I read they're suppsed to protect from blowing the fuse from

inrush current, The main fuse is 3.15A, so that's why I went with a 3A.

When I tried the first power up after replacing those, I half expected it to pop the fuse again. I figured it couldn't be that simple.

But when I hit the power switch, I heard the CRT fire up. (That quick hum sound--Degauss?) Hit the switch on the keyboard and got a chime.

No problems yet-- Maybe I got lucky, and it was just the switching FET that failed.

I'll eventually recap the analog board, probably sooner than later.

 

[techknight]

They do fail, but when they do they usually take the SMPS IC out with it. 

 

[uniserver]

Ah ha!   for a moment I thought he had figured out what was causing the Color Classic Boards to be dead.

There is like 3 other threads about CC's goin.     But good job on fix'n up the A/B!

back to the mystery of the dead Color Classic MOBO's