5150 Rescue and Repair

[modem7]

... including the 3 socketed replacements borrowed from bank 3 and placed bank 0 - (which RDR is now saying are faulty).

Clarification for readers. RDR indicates that 'bits' are faulty, not RAM chips. Accordingly, RDR displays, "<----- May or may not be RAM chips." to the right of the bit pattern. (As pictured in post #38.)

But if anyone is aware of a specific technique for desoldering the DRAM chips on the 5150 I'd love to hear it, as ...

The active thread at [here] may assist you.

 

[oldpcguy]

Just an update as I won't have much time to work on it now for a couple of weeks but this thread is serving as a bit of a handy journal too . I've built a DRAM tester and it's confirmed that the 3 x 4116 chips I pulled from bank 0 and the one from bank 3 are faulty. I've also tested the remaining socketed chips and they report as good - including the 3 socketed replacements borrowed from bank 3 and placed bank 0 - (which RDR is now saying are faulty). I did have to install some bodge wires sadly but all the continuity checks out with regards to the other RAM banks but of course there's always the possibility of I've either made a mistake or inadvertently damaged something else. U12 I can actually test externally and even have a replacement, but of course would require desoldering from the board which I'm not in a hurry to do at this point. But if anyone is aware of a specific technique for desoldering the DRAM chips on the 5150 I'd love to hear it, as trying everything from fresh solder, to braid and flux to using the desoldering gun I did struggle to find a technique that worked consistently on every pin

My technic is to use my Hakko desoldering gun to remove the bulk of the solder and then use hot air. When using the hot air I move it back and forth over all of the pins while lightly pushing down on the end pin where I currently have the hot air pointing. At some point the pin will push down and then I work my way to the other end of the chip. IMO it's important to be moving the hot air over all the pins and not focusing on any specific area for too long. This technic has worked great for me, I've even used it to remove some 40 pin DIPs and I am going to utilize it to try my hand at removing a 30 pin SIMM socket.