Entech 203.2 mods - What wattage soldering iron?

When I mod, I use both a desoldering pump/iron (the desoldering iron from Radio Shack), and desoldering braid. With that combo, I replaced about 50% of the parts on a M-audio SuperDAC 2496, including 6 DIP opamps, ~25 electrolytic capacitors, another 12 or so ceramic caps, along with a few resistors.

I personally think the two work well in tandem -- if the desoldering iron can't suck out all of the solder, then I hit the part with the braid. Anyways, both the braid and the desoldering iron are pretty cheap (about $15 total) at radio shack. so I don't think you have anything to lose by getting both.

Someone on these board mentioned that it's easy to burn Cruncher PCB. If you have no previous expirience with desoldering parts from PCB, better exercise some on an old board - it's definitely harder than soldering. Generally, never pull hard and wait for the joint to melt or you could tear traces from the PCB.

Here's what I do:

1)2-leg elements are easy with repetitive heating and pulling slightly side by side. Strat with the larges ones to clear space. You could put some more solder on ground plane jonts - these are the hardest to melt. Ignore residual solder in the holes at this time
2)3-6-8 leg element - put a blob of solder on one side and trying to melt all at once and gently pulling that side up a bit, than on the other etc...have to be creative here
3)Cleaning the holes by going with the iron from the top side and with the pump from the bottom, holding the board in small vise. I have braind but alomst never use it except for SOIC pads

I'm using 800F 1/32" conical Weller tip on 201 soldering station.

The kind of pump that poses a slight risk is the simple spring-loaded type, as it can kick back and strike parts. The bulb type motherone mentioned is safer, as is braid/wick.

If you want advice more specific to that DAC or the mod(s), you should link to good sources of information for these, good pictures too if possible.

If you are going to do more DIY, I think it is very worthwhile to get a good, temperature controlled iron. I bought a used hakko a while back, which was not that expensive, and it works very well. Better irons also have different size tips available, so you can buy a fine tip for surface mount, and a big tip for soldering something large.

For removing a chip, I think the easist method is to cut it off. You obviously end up throwing it away, but I think there is much less chance of damaging a board this way, unless you have very expensive desoldering equipment.

Randy

Entech Mods

I used a 60w temperature controlled Weller (W60P) with a 700 degree tip (PTA7). I probably should use a 600 degree tip but the 700 came with. This iron is really too big for surface mount components. I also have a Weller WM120 which is a small 12w iron but it gets too hot; I have to be careful and quick on the surface mount components.

I have several bulb-type vacuum desolder tools. My favorite is small and has a short teflon tip, but it's not powerful enough for some jobs. The small braid is also useful and I use paste rosin flux if needed. Oh and I use the very fine diameter (0.015 inch) silver-bearing solder for circuit boards.

I use q-tips and cotton balls (rayon cosmetic puffs actually) to clean the flux after each step. "Oops!" is a good solvent but "Goof Off" is too strong as it melts some plastic components. Polystyrene capacitors are very fragile and are usually hand soldered to avoid damage from heat and solvents.

I'll post some pics after I get them off the camera.

You can't beat hands on .....get a solder sucker

antex 15 watt fixed temp should be good enough not to get you into too much trouble!

there some good advice on the preceeding posts too...

Entech 203 Mods (pics)

I didn't do the wild monkey mod, just the socket for the op-amp and a connector for the LED.

The eight screws which hold the extrusion for left-top-right sides are torx t-9 and not too hard to remove considering they have been tight for about 9 years. From the date codes on the chips (late 1996 and early 1997) I guess the unit was assembled in late 1997.



The LED is hard-glued to the front panel and hard-wired to the PCB, a real PITA since the panel extends under the front of the PCB and there are no supports. So I just cut the LED wires to simplify the whole process of disassembly, modification, and re-assembly.



to be continued...

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Entech 203 Mods (continued)

The screws holding the back panel to the connectors were difficult to remove as they were very tight in the hard plastic. After I got them out I cleaned the threads and put a little grease on them so they won't be so hard next time.

Since I didn't need to recover the amp soldered on the PCB I just clipped the leads on one side.



After clipping the leads on the other side the chip was free leaving the 8 legs on the top of the board.



to be continued...

Entech 203 Mods (continued)

Now to remove the leads and clean up the holes. If you look at the back side of the PCB it looks something like this.



The amp layout is in the top left, below the output RCA sockets. The next step is optional. Carefully heat each pad and work the lead down towards the top side; this will make it a little easier to remove the leads from the top.

Notice the flux puddles left when the poly caps were hand soldered. These flux puddles have had about nine years to dry so they are difficult to remove. If you don't care just skip this part; this is my hobby and a labor of love so I broke them up with a toothpick. Don't scratch the fiberglass or the solder mask with a screwdriver, it will only look worse.

From the top side of the board, carefully heat each pad/lead joint and remove the lead with a small pliers or tweezers. Do not touch the poly caps with the soldering iron tip as they will melt easily. It will be easier to do the next step from the back side of the PCB. Apply a small bit of paste (rosin) flux with a toothpick or q-tip stick. Then carefully heat each pad and remove the solder from the hole with a vacuum bulb or solder wick. The wick (braided copper ribbon with flux) works well on surfaces but may not work well on small holes. It may be necessary to heat each pad and clear the hole with a pointed toothpick. If the holes are clear it will look something like this (sorry, this pic is a bit blurry).



Once the holes and pads are clear of excess solder, clean the flux from both sides with a q-tip soaked with solvent. This is also a good time to mop the rosin from the poly cap pads.

WARNING:
Some solvents will melt polystyrene and other plastics used in electronic components. Most effective solvents are a mixture of alcohol, petroleum and/or chlorinated hydrocarbons. THIS STUFF IS DANGEROUS AND WILL IGNITE. Also don't breathe the fumes; I know it's fun but this will damage your nervous system.

To be continued...

Entech 203 Mods

OK, so after a little cleanup the top side looks like this.



Notice the white outline with a notch towards the front. The notch on the outline (and the socket) indicates pin #1 on the chip. Install the socket with the same orientation. Solder the socket leads from the back side. The joints should be smooth, shiny, and symmetrical.



If you have a pin connector like they use on PC motherboards, you can use it for the LED. The pins and holder are soldered to the PCB between R22 and R23 (I think it's labeled D5).



Cut the wire with sockets down to 2-3 inches and solder the free ends to the LED. Heat shrink is nice but not necessary, just keep the LED leads from touching. Put the sockets in the connector housing (they snap in to a retainer in the plastic). Don't worry about polarity; if it doesn't work just reverse the connector on the pins.

Clean up the rosin from the back of the board. Put the new amp in the socket (pin #1 towards the front) and re-assemble the chassis. There is no support on the front panel so put a plastic bag or something under the board to insulate the bottom while testing. I taped the bag on for safety and also taped the two halves of the chassis on the bottom to hold it together.



After testing, remove the plastic bag and replace the top cover.