HP545 repair, desoldering the NVRAM.

[Arjan Emm]

I have an old HP54503A that has lost it memory . The NVRAM died. Realtime bandwidth is useless on this old machine with 20M/s, but it's a real nice machine to work with, up to say a MHz, so i like to keep it in working order. The old DS1235YW-120, 28 pin sram can be replaced with a DS1230-120 that's still in production and i sampled one.
Question, how to desolder the old ds1235. It's on a 3 or 4 layer board. I first resoldered all the pins. Then i used a pen style solder sucker to remove the bulk of the solder. And used solder wick after that. But it's stuck as a brick.

How do you remove such a bastard with 28 pins, you can't cut the pins individually and pull em out because you can't reach them because the package is wider as standard dip. And i don,t want to ruin all those nice gold plated  .5 mm traces.

[xrunner]

I have an old HP54503A that has lost it memory . The NVRAM died. Realtime bandwidth is useless on this old machine with 20M/s, but it's a real nice machine to work with, up to say a MHz, so i like to keep it in working order. The old DS1235YW-120, 28 pin sram can be replaced with a DS1230-120 that's still in production and i sampled one.
Question, how to desolder the old ds1235. It's on a 3 or 4 layer board. I first resoldered all the pins. Then i used a pen style solder sucker to remove the bulk of the solder. And used solder wick after that. But it's stuck as a brick.

How do you remove such a bastard with 28 pins, you can't cut the pins individually and pull em out because you can't reach them because the package is wider as standard dip. And i don,t want to ruin all those nice gold plated  .5 mm traces.

It's hard. You are doing it the way I've done it in the same situation. I've done it before but it's tough, tough, tough -

Xrunner's HP 54501 restoration

I was very worried that I wouldn't get it out without ruining the thing. I also put in a socket after I got the bastard out.

What you might have to do is get a real desoldering system, but maybe you'll get another idea in the thread. 

[RayRay]

You probably still have some solder stuck in there!
I'd suggest you add a bit of solder to each joint, apply flux on em, and then use a wick on top of em with your iron.
Using flux in combination with a wick often yields much better results than just using it standalone.
Alternatively, you could use a hot air station instead to heat up the whole area and gently pull it out at the same time.

[xrunner]

Arjan - what are you going to try next?

[Arjan Emm]

Nice restore Xrunner.

I think I'm gonna try a gas fired 3Kw plumbing iron on it. These are used for zinc roofing and gutters, soldering meters of 1mm thick zinc or copper plates together. This may sound crude and yes, I will test it on some old boards first before I have a go at this beautiful board.
These are actually nice irons to adjust if you get a feel for them. I have access to a couple of them with tips ranging for 2x17mm like in the picture, to 10x50. I can also solder lead with it that melts at only 325C while the solder melts at 260, so it's pretty accurate with lots of thermal capacity.

So I plan to resolder all the pins for good thermal connection through all the layers and desolder it in one go. Maybe one row at a time.

[xrunner]

Nice restore Xrunner.

Thanks.

I think I'm gonna try a gas fired 3Kw plumbing iron on it. These are used for zinc roofing and gutters, soldering meters of 1mm thick zinc or copper plates together. This may sound crude and yes, I will test it on some old boards first before I have a go at this beautiful board.

Interesting idea - keep us updated! 

[MarkL]

Wow, I don't think I'd go anywhere near delicate electronics with a gas iron like that.

One way is to get a bar tip (and the unit that goes with it).  For example, here are some offered by Aoyue:

  http://www.aoyue.com/en/products/?bID=133&sort_id=167&page=2

The 40mm one, WQ-1402, would do nicely for 28 pins.

I'd blob solder on all the pins, heat one side until all the solder flows, and then lift the side very slightly.  Then do the same to the other side.  Alternate sides until it's all the way out.  Use lots of flux and a gentle touch.

I'd recommend putting in a socket instead of soldering in the new part.

[JFJ]

... I plan to resolder all the pins for good thermal connection through all the layers and desolder it in one go...

I wonder if ultra-low melting point ChipQuik solder (intended for the removal of SMD components) would be of help with your plan?

Dave did a ChipQuik review video:

[senso]

My plan of action would be to use an hot air station, and evenly heat the board for around 2 minutes, then, with lots of flux follow the pins around while still keeping the hot air going, the chip will just fall off the board, but I reckon that you need at least 4 hands for that.
At work I have a bit IR station with pre-heat/heated bed that is a joy to use in those cases.

[Arjan Emm]

Thanks for the input everyone!
I used an old iron with a 35 by 8 mm tip and just heated it with a gas torch for a few minutes till i took solder. cleaned it on a sponge and applied the 500 gram block of copper to one row of pins. Within 2 seconds the whole row of 14 came out, same for the second row. All vias, pads and traces survived. Crude but effective, with actually minimal amount of heat stress to the board and the chip. From here on I went back to the normal soldering station and wicked the vias clean with litze before soldering in the new NVRAM. And the scoop regained it's memory! All self tests passed and remains in calibration after power off.

[Samogon]

I would not call it crude, it is ruther elegant solution not having expensive desoldering stations.
Congrats on repair.

[james_s]

I use a Hakko 808 for this sort of thing, wonderful tool, I had no trouble removing the Dallas chips from my recently acquired TDS784C with it.

Not that it matters now, but it's actually possible to replace the battery with the chips in place if you don't want to try pulling them. There are some videos out there that show the details, but essentially you grind into just the right spot with a rotary tool to expose the leads to the battery. Sever them and solder wires to an external battery, CR2032 holder glued on top of the chip works well. If you're careful you can even attach the new battery before disconnecting the old one and retain the memory but that's tricky.

[MarkL]

... I plan to resolder all the pins for good thermal connection through all the layers and desolder it in one go...

I wonder if ultra-low melting point ChipQuik solder (intended for the removal of SMD components) would be of help with your plan?

I always wondered that too.  I use ChipQuik for SMDs all the time.

I decided to try it on an old board with a 28-pin ceramic DIP.  It worked pretty well, but I needed to use a lot more ChipQuik than I would normally use on an SMD part.

I think I'll continue to use a bar tip, or as someone else mentioned, a good ole' SoldaPullt (solder sucker).  If the pads were in bad shape and needed extra care, I would probably opt for the ChipQuik.

[xrunner]

Thanks for the input everyone!
I used an old iron with a 35 by 8 mm tip and just heated it with a gas torch for a few minutes till i took solder. cleaned it on a sponge and applied the 500 gram block of copper to one row of pins. Within 2 seconds the whole row of 14 came out, same for the second row. All vias, pads and traces survived. Crude but effective, with actually minimal amount of heat stress to the board and the chip. From here on I went back to the normal soldering station and wicked the vias clean with litze before soldering in the new NVRAM. And the scoop regained it's memory! All self tests passed and remains in calibration after power off.

I hope you put a socket in there but I doesn't look like you did ... 

[james_s]

What I'd like to know is what they were thinking not putting a socket in there from the factory. Planned obsolescence? But surely most people who know how to use equipment like this know how to desolder and replace a chip, it's just an inconvenience.

Oh and regarding ChipQuik, it's totally neat stuff but the challenge I had with it was cleaning it all off the pads and/or the IC if I wanted to reinstall. If you leave much of it behind the solder melts at a very low temperature and hot running parts can unsolder themselves.

[MarkL]

Oh and regarding ChipQuik, it's totally neat stuff but the challenge I had with it was cleaning it all off the pads and/or the IC if I wanted to reinstall. If you leave much of it behind the solder melts at a very low temperature and hot running parts can unsolder themselves.

I've never had chips unsolder themselves, but I've had problems soldering to pads or pins after ChipQuick has been on them.  The surfaces sometimes appear dull gray, perhaps from oxidation, and fresh solder does not flow easily even with extra flux.

Before remounting a part, re-tinning ChipQuik'ed pads/pins with regular solder and then removing the excess with solder wick restores a good soldering surface.  It's part of my routine when using ChipQuik.

[Rasz]

One way is to get a bar tip
I'd blob solder on all the pins, heat one side until all the solder flows, and then lift the side very slightly.  Then do the same to the other side.  Alternate sides until it's all the way out.  Use lots of flux and a gentle touch.

this, but instead of just solder blob use old solder filled desoldering braid - it has a ton of thermal mass and will conducts heat to all the pins in a row
personally I would use hotair in the first place

[Armadillo]

Arjan, thanks for the method, considering that chipquik is not so Cheap, I should get one of the iron myself. Never try, never know.