I've got an Apex 660 DVD player that I'm trying to repair. It's has very low analog sound output (that is, you have to turn the TV all the way up just to hear the sound). There's a separate circuit board that contains the A/V outputs and associated circuitry.
I'm pretty sure that the two little JRC4580 op-amps on the board are the problem. Trouble is: They're these little 4x4 SOIC chips soldered to the BOTTOM of the board (whereas everything else on the top are conventional through-board components). I found out via Mouser that the LM833 is an equivelent that can replace the 4580.
My question is: How exactly does one desolder these things? Should I put the board in the oven like that dude about a dozen posts up did w/ a video card (I did get a bit of a laugh out of that)? Currently, I've replaced all the electrolytics and a few transistors (S8050, 9014,
9015), but the problem still remains, which leads me to suspect the chips.
Use a fine tip soldering iron, desolder 1 pin at a time and then lift the pin up using a sharp needle or something similar, work on all the pins and this way you will free the IC without damaging any of the traces, of course your IC can no longer be used so if you still want to reuse it you will probably need to heat the area with a heat gun.
If you want to go the heat gun route protect the surrounding areas with a thick cardboard/plastic mask and then let the IC fall off once heated.
What type of iron would you recommend? I don't think my $12 RatShack one is going to work since it has a wide conical tip. One w/ a needle tip? I don't need to worry about reusing the old chips since I ordered and received the replacements from Mouser. Just that I get them off without taking the solder pads w/ them.
That iron should work fine, it's not so much the tools but the skill and patience of the person using them that matters. I've used a heat gun to desolder chips too.
If you take a piece of thin single strand wire, such as rework wire, thread it through behind the pins, and tack solder its end to any convenient solder point nearby, you can then pull the long end outwards away from the pins, keeping it as flat to the board as you can. Then touch the first pin that's holding the wire from moving, with the tip of your iron. So if you're right handed, with the row of pins that you are desoldering facing away from you, you will have threaded the wire through from left to right, and tacked its right end down. You will now have the free left end in your left hand, and the soldering iron in your right hand. As the joint melts, and wait a second or two so that it has *thoroughly* melted, pull a little harder on the wire. It will slide out from under the pin, taking any solder with it, and will also lift the pin very slightly clear of the pad. Repeat for each pin until the wire comes free from under the last pin, then repeat for the other side. If the IC looks like it's on the move as you unsolder the other side, stop when you get to the last pin, and just heat that one whilst lifting the device off the board with tweezers. If the chip remains fixed to the board by glue, then unsolder all of the pins with the wire, then use an old scalpel to get in under the chip, and twist to break the glue seal.
Before fitting the new chip, you must remove any glue fragments from the board, and you must carefully remove as much as possible of the original solder from the pads, using a good quality de-solder braid. Place the new IC as accurately as you can, then tack one corner pin, using as little solder as you can. Now carefully examine your positioning to make sure that *all* legs line up correctly with their pads. Adjust if necessary. It is now pretty much essential to run some liquid flux in around all the pins, before soldering them with a clean fine tipped iron, and fine gauge solder. After doing this, I would strongly recommend cleaning the whole area with a defluxing agent, and then examining your work with a strong magnifier, or better, a jeweller's loupe.
For what it's worth, I actually think that replacing the ICs is highly unlikely to cure your problem. Before going down this route, have you checked *very* carefully that there is not a menu setting that disables the PCM audio analogue mixdown ? Such a setting may be several layers down in audio or system setup. Failing this, have you checked that the IC's have both a positive and negative supply on them ( pins 4 and 7 from memory, but check this ) ? There are several makes and models that suffer from the symptoms that you have described, and the problem is that one or other of the rails to the output buffer opamps, is missing. It is usually caused by a short circuit rail decoupling capacitor, and the only aspect of operation of the machine that's affected, is the analogue audio. If one of the rails is missing, look for a couple of caps, probably something like 47uF or 100uF, nearby the IC's.
Hello, Madness! You wrote on Fri, 22 Sep 2006 22:29:13 GMT:
What type of iron would you recommend? I don't think my $12 RatShack one is going to work since it has a wide conical tip. One w/ a needle tip? I don't need to worry about reusing the old chips since I ordered and received the replacements from Mouser. Just that I get them off without taking the solder pads w/ them.
What I sometimes do is take a few inches of solid copper, fairly heavy guage wire, and wind it around the element and tip of my old weller 25W soldering iron. Wind it around about half a dozen times leaving a short length extending from the tip. Cut the end into a chisel point and clean and tin it with solder. I find this a useful tool for fine work if you don't do enough SM stuf to justify a proper station. You can use finer wire of course to make an even smaller point but on the smaller scales the surface tension of the molten solder becomes a problem.
With best regards, 3T39. E-mail: snipped-for-privacy@hotmail.com
*Any* soldering iron will work. I get mine at those Chinese dollar stores for, yep, $1. You know, you can file the tip to any shape you like. You're not stuck with shape of the tip as sold.
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The Zealots won against the Romans, and Ehud Olmert won the Second
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That used to be a lot truer in the old days when the tips were made of copper, but now that they are all iron clad or nickel plated, I find that taking a file to them results in their rapid demise, especially with the more aggressive fluxes that they are having to put in the lead-free crap solder to make it stick to anything ...
Probably not so much of a problem if you are a hobbyist who takes his iron out once a month, uses it for 5 minutes, and shuts it off again, but definitely is if your irons are on 12 or more hours a day, as mine are.
So, what a guy would want to do, maybe, is replace his tip with a piece of copper bus bar or ground rod, say? Would that be better?
I'm definitely in the first category. Maybe once-three times a week.
--
Napoleon won the battle of Waterloo. The German Wehrmacht won World War
II. The United States won in Vietnam, and the Soviets in Afghanistan.
The Zealots won against the Romans, and Ehud Olmert won the Second
Lebanon War.
- Uri Avnery, Israeli peace activist
(http://counterpunch.org/avnery09022006.html)
You're probably OK then. I doubt that filing down would have much impact on your tip life that you were bothered about. I used to prefer tips when they were all copper, as when they did oxidise up, you could indeed just file 'em up to a new tip shape, and re-tin. I used to use an old Adcola years ago, that employed pure copper tips, and you used to be able to use and file until you were down to like a half inch long, before you had to replace.
These days, I keep replacement tips for all of my irons in stock. I suppose that I shouldn't imply that there's anything wrong with iron clad tips per se. Initially, they definitely provide a ready-tinnable tip for much longer than the all-copper ones did. But once they start to go, and stop tinning, for sure you can get them back by lightly filing, but you'll then find that inside a couple of days ( of 12 hours a piece ) you've got a dirty great crater in the tip, and there's no option but to replace. Most of the irons that I use are thermostatically controlled, so I would guess that the tip design and materials, are carefully selected by the manufacturers to produce a good tight control loop, and subbing for copper rod or whatever, would probably not do the performance any favours. In fact, it might be quite hard to do these days anyway, because most tips have particular shaped bodies to fit their intended irons, but if you are just an occasional user, with an iron that uses the sqeeze up collar type of tip mount, then you might well find that you prefer a home-made all copper tip to the one originally fitted.
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