A1200 audio problem

[coze]

do you have audio output from paula ?

solder a couple of wires to paula left and right output and see if you have sound. it will be very high, distorted because you're by passing the filter. but it will save you from changing paula if nothings wrong with it.

personally I think you should supply +12v directly to op amp.

[elspero]

Unfortunately I don't have the tools. Otherwise I would already have desoldered and cleaned under LF347.

But I don't think Paula or LF347 are faulty. It's what arrives to LF347 that is wrong.
All the capacitors I changed had leaked a little, but I haven't seen broken vias.

The point is: R301 has +12v. From the schematics (audio decoupling) it should go directly to LF347 pin 4. It doesn't. From what I can see, from C303 the via goes under LF347.
What happens if I connect a wire from C303+ to LF347 pin 4?
Does anyone know where I can find a picture of the board with LF347 removed?

[elspero]

Originally Posted by coze

do you have audio output from paula ?

solder a couple of wires to paula left and right output and see if you have sound. it will be very high, distorted because you're by passing the filter. but it will save you from changing paula if nothings wrong with it.

Well, there's audio, but it has low volume, occasional popping and distorted sound.
Should I solder a wire from pins 33 & 34 and feed it to the TV directly?

personally I think you should supply +12v directly to op amp.

See my post above this one, feed from C303 to pin4 of op amp?

[coze]

Originally Posted by elspero

The point is: R301 has +12v. From the schematics (audio decoupling) it should go directly to LF347 pin 4. It doesn't. From what I can see, from C303 the via goes under LF347.

well, it sounds like it. just connect a wire from LF347 pin 4 to R301.

[elspero]

Ok, thanks. I have to go to work now, I'll report back later.

[Loedown]

Any leakage can be enough to chew tracks away the outside view of LF347 can be all rosy, but underneath it's rotten track hell.

[elspero]

We're almost there! Connecting pin4 to R301 or C303 restored almost all the sound.

BUT it looks like one of the channels has problems. I tested it with "into the wonderful", and some sounds are missing now and then. It doesn't look like a frequency problem, as only some samples are missing. But the defects are always the same ones, so it's not random.
I'll have another go trying to desolder lf347, but I only have a soldering iron, no hot air.

In the meantime, suggestions regarding how to fix defective audio channels are more than welcome!

[elspero]

No success with LF347. I don't have the proper tools for smd.
Could the sound defect be caused by it?

I tried connecting the audio output directly from paula, but the audio is very low and I can't understand if it's working properly.

What would be the best course of action now?

[kipper2k]

Originally Posted by elspero

No success with LF347. I don't have the proper tools for smd.
Could the sound defect be caused by it?

I tried connecting the audio output directly from paula, but the audio is very low and I can't understand if it's working properly.

What would be the best course of action now?

.

If youre in Canada and want to send it to me i can replace paula and the lf347

[elspero]

Thanks for the offer kipper2k, but I am Europe. Shipping would cost more than a full A1200 setup :/

[Loedown]

Hassle Zetr0, he's in UK, I'd do it but I know what it would cost to send it to Australia.

[Hewitson]

Simply cut the legs of the op amp with a knife and remove the chip, then remove the legs with your iron.

Soldering the chip will be very easy if flux is used.

[pandy71]

Also serial port translator 1488/1489 are responsible for strange things - at least one person made ale replacement for this - not so long ago - check history

IMHO replace them for something decent and more modern like MAX232 or similar - usually faster and simpler application circuit.

[Loedown]

Originally Posted by pandy71

Also serial port translator 1488/1489 are responsible for strange things - at least one person made ale replacement for this - not so long ago - check history

IMHO replace them for something decent and more modern like MAX232 or similar - usually faster and simpler application circuit.

Or just simply ask Maxim for samples, they do a 1488 and 1489, I got some sent to me several years back.

[Loedown]

Originally Posted by Hewitson

Simply cut the legs of the op amp with a knife and remove the chip, then remove the legs with your iron.

Soldering the chip will be very easy if flux is used.

Oh good another butcher, what happens when the knife slips and cuts the tracks underneath?

Clip the leg leads with sidecutters then desolder the leg stubs from there. but be warned, use very fine sidecutters as they limit the amount of stress placed on the pads, always cut from directly above not from the side.

[Hewitson]

Think you're more likely to do damage with a pair of sidecutters to be honest. Never slipped once with my little craft knife.

I don't really appreciate being called a butcher, I take a lot of pride in my work and have never damaged a board in my life.

[kipper2k]

To remove SMD's you MUST use a hot air rework station especially if the chips are 4 sided, you can remove the chips quickly and prevent damage and bending of the legs.

here is a link for same model i use...

http://cgi.ebay.ca/SMD-Rework-Solder...item43a0af3e52

Set the temp at 350 deg and use the smallest nozzle, i actually took the small round nozzle, and squished it flat to elongate the nozzle to give more control. Practice removing components on an old board, you do not need a lot of air flow (especially on a densely packed board).

You would be surprised how much heat these chips can actually take, saying that, make sure you direct the air flow to the legs only, constantly moving back and forth and side to side, do not heat the chip up directly. it would take about 10 seconds to remove the LF347 for example, with no stress on the pads

It is not hard, a bit of practice and you will be impressed with yourself.

[pandy71]

It can be removed (by normal solder iron) by putting very thin steel (or similar not very well solder-able material) between legs and pads on PCB - for example blunt razor blade or event better one of thin feeler gauge sheets.

If You use hot air it is better to cover surrounding areas by some thermal insulator - like glass fiber mate - easily available due of frequent use for repairing composite structures (cars, yachts...) - can be easily cut by scissors. More expensive (but slightly better) is kapton tape - yes it is used in industry for thermal protecting many sensitive devices.

[Loedown]

Originally Posted by kipper2k

To remove SMD's you MUST use a hot air rework station especially if the chips are 4 sided, you can remove the chips quickly and prevent damage and bending of the legs.

here is a link for same model i use...

http://cgi.ebay.ca/SMD-Rework-Solder...item43a0af3e52

Set the temp at 350 deg and use the smallest nozzle, i actually took the small round nozzle, and squished it flat to elongate the nozzle to give more control. Practice removing components on an old board, you do not need a lot of air flow (especially on a densely packed board).

You would be surprised how much heat these chips can actually take, saying that, make sure you direct the air flow to the legs only, constantly moving back and forth and side to side, do not heat the chip up directly. it would take about 10 seconds to remove the LF347 for example, with no stress on the pads

It is not hard, a bit of practice and you will be impressed with yourself.

LF347 is just a standard SOIC, pins on two sides easy to take off.

[Loedown]

Originally Posted by Hewitson

Think you're more likely to do damage with a pair of sidecutters to be honest. Never slipped once with my little craft knife.

I don't really appreciate being called a butcher, I take a lot of pride in my work and have never damaged a board in my life.

I take a lot of pride in the work I do as well, in my younger times I damaged plenty of boards and that's what taught me techniques to avoid said damage again. One of my first roles was repairing power supplies that their capacitors had leaked and caused massive damage to the pads / boards. What we were shown to do was to scrape the solder resist back and to use the legs of the capacitors to reinforce the tracks. I then used to use scrap boards to learn how to take off and put on SMD components in my spare time so that now when I have an A4000 or A1200 main board sitting in front of me I am confident that I can repair them without damaging the board and if the board has already been damaged by corrosion either through caps or battery, then I can fix that too.

The point you missed in this thread is that the owner of the board is an amateur, craft knife expertise in removing chips isn't recommended for amateurs, more to the point SMD isn't recommended for amateurs but if people are adament that they want to try advanced techniques on a board to save a few dollars on a repair that could be done by someone competent and run the risk of destroying their boards that's fair enough, I just try to offer advice based on sound techniques that I know work and that are easy.

I would personally use hot air to take the chip off, if I didn't have that a fine iron and a dental pick, even the latter can't be done without having some practise prior and as a last resort the sidecutter technique mentioned earlier.

By the way, if you use very fine sidecutters from directly above you cause minimal disturbance to the pads, but if they're not fine then you run the risk of clipping a second leg at the same time and putting a sideways shear on one or both pads.