- VCF South West - June 14 - 16, Davidson-Gundy Alumni Center at University of Texas at Dallas
- VCF West - Aug 2 - 3, Computer History Museum, Mountain View, CA
- VCF Midwest - Sept 7 - 8 2024, Schaumburg, IL
- VCF SoCal - Mid February 2025, Location TBD, Southern CA
- VCF East - April 2025, Infoage Museum, Wall NJ
-
Please review our updated Terms and Rules here
5150 Rescue and Repair
- Thread starter Oddsocks
- Start date
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.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
I'm noticing that the bits reported as faulty do change slightly each time I power cycle the system. Is that more suggestive of an issue with U12 than the RAM itself?
Finally got some time to look at this again. I'd previously replaced 3 faulty RAM chips in bank 0 and 1 in bank 3. Then I was getting the previous memory error about the first 2K failing. Examined the sockets under a microscope and noticed the tiniest bridge between one of the pins and a trace that ran between it. I could barely make it out with the magnifying glass which I'd use previously. Removed the solder bridge, discovered I actually had 4 spare 4116 TMS DRAMs in stock from a TI/994A project, stuck them in and got this. Now the slow refresh issue doesn't seem to follow the chip, always seems to be at the same address, but I'll need to double check that.
Attachments
I'm thinking there's even a chance this my show something with the original ROM now, which would be a major milestone with this for me
modem7
10k Member
Something to check, and put aside:
The 4116 RAM chip uses +5V, -5V, and +12V. Do those three voltages measure (at the RAM chips) with the ranges shown below, which is what I see in three 4116 data sheets that I looked at.
The 4116 RAM chip uses +5V, -5V, and +12V. Do those three voltages measure (at the RAM chips) with the ranges shown below, which is what I see in three 4116 data sheets that I looked at.
modem7
10k Member
Yes, the IBM BIOS ROM may now show an output.
modem7
10k Member
I have a RAM chip that fails the 'slow refresh' test. I use it in regression testing of new versions of Ruud's Diagnostic ROM.