Matsui MCT640

[simpsons]

This receiver uses the uPC1420 all-singing video demodulator, chroma and deflection ic.

When first switched on the set displayed an excellent picture and sound but soon showed its true colour.

When off tune video noise is shown on the CRT and white noise for sound.

However, when tuned correctly the screen displays a blank raster and the sound is muted.

There is some colour burst noise when rotating the tuning off station but that is all.

FM Radio is fine and although when switched off for some time, I can no longer get the set to work properly as in para2. Just the blank screen etc.

Before I order a replacement ic with its 48 legs any other ideas where the fault might be.

Chris

[agardiner]

Just taken a quick look at the schematic. Assuming the power supplies to the IC are correct, then my money would be on the uPC1420. Might be worth a squirt of freezer on the IC to see if that brings back the picture, just to confirm.

[simpsons]

Many thanks Adrian for your comment.

Inside my workshop, where the set was first switched on, the temperature was 30 degrees Centigrade so I placed a fan above the ic to cool things down. No difference

I don't have freezer spray at hand but will follow your advice and see what happens. If only I could get my better half to allow me to put the set in the fridge!! Wishful thinking I'm afraid.

This ic. has 48 legs, help!

Chris

[G6Tanuki]

If it's a 48 legged IC of the dual in line style then the best way to remove it if you haven't got a professional desolder thingy that heats all the leadouts together, is to use some very small side cutters to cut all its legs off then hoick out the body and remove the remains of the legs one at a time.

That will give you the least likelihood of damage to the PCB.

[simpsons]

Thank you G6 for your advice.

I did wonder how on earth I could get the ic out without damaging the pcb.

Just before I saw your welcome procedure, I looked at a YouTube video in which the publisher used a 22 gauge copper wire, bent to fit between the ic pins, pre-fluxing the whole then heating the wire with 40/60 solder flowing to distribute the heat.

Although it wasn't an ic but an ic socket being removed, the procedure was successful as before your very eyes, the socket just fell off the board.

Cutting the pins though may well be the best bet.

Many thanks

Chris

[Maarten]

A good quality desoldering wick (chem-wik) will work wonders. 22 gauge copper wire might work but I wouldn't take the risk.

[gallowfields]

yes quite easy to do with desoldering braid
brian

[simpsons]

Thank you all for your suggestion and Maartin and Brian for giving me confidence in removing the IC.

A new IC has been purchased and the recommended de-solder braid is in 2mm width format.

I do have some very fine-jawed side cutters to sever the legs of the IC if needed and together with a fine point soldering iron tip and de-solder braid, all should be well.

I will update the post when the job is done.

Chris

[gallowfields]

hi, i would,nt think you would need to go down the road of cutting the legs , just use the desoldering braid and a fine tip iron and you will find you are able to remove the i/c intact and leave the print in good condition. i have removed quite a lot using that method and also the desoldering pump method
regards brian

[simpsons]

Many thanks Brian

All advice is gratefully received.

Chris
PS Apologies Maarten for misspelling your name.

[Maarten]

No problem, for my job I regularly mail with people all over Europe to provide technical assistance an it would surprise you how many people only remember the approximate sound of a foreign name instead of the spelling.

In any case, I think you'll do just fine With the IC.

As a few last bits of advice, a flat tip or a tip with a flat side will usually work best to transfer the heat into the wick, or if you use a conical tip, apply it so the contact surface between the tip and wick is maximal.

Sometimes it can help to add a little bit of solder or a little bit of flux just before or during the wicking, though if the wick is fresh it should usually get going on just its own flux.

[simpsons]

Many thanks Maarten

I too found that adding flux or 60/40 solder to an old joint works wonders before trying to desolder a component. I use plumbers flux although there are products specifically designed to be used in the electronics field.

It does seem counter-intuitive to add solder to a joint before using a desolder tool or wick but it works. I read that it is because the joint oxidizes over time forming a "cold" joint.



Chris

[Maarten]

Plumbers flux can be corrosive and/or conductive and should be toroughy cleaned up immediately after use, but I'd rather use no additional flux than plumbers flux.

[simpsons]

I'm so glad others are reading my attempt to desolder the IC.

Now I know what the idiom "A little knowledge is a dangerous thing" means.

In my defense, I have dipped the soldering iron tip into the flux rather than paste it onto a soldered joint.

The IC is now with me, just waiting for the recommended de-solder braid to be delivered. Then, with my old habits put to one side, the IC will come out and the new one in its place.

Chris

[simpsons]

Thank you all for your help in fault finding, guidance and recommendations.

The TV works a treat. What a good CRT with excellent resolution and grey scale clearly showing the dots on test card F.

Adrian, you were spot on. A new IC did the job. G6, Maartens Chem Wick was just the ticket, there was no need to cut the legs. Thank you Maarten for the recommended product, it does work very well and last but not least, Brian for giving me the confidence to follow Maarten's advice.

The 48-pin IC came out quickly; well, that was after the hot glue had been dealt with. The pin spacing was a little tricky when soldering but, "Specsavers" aside, the illuminated magnifying lens was christened and the flux turned out to be electronic flux! No wonder my plumbing was, shall we say, not quite as good as it should be.

Chris

[agardiner]

Result! Well done.