Apple IIc memory chip replacement

Here is the schematic for the //c:

http://www.applelogic.org/files/IICSCHEMATIC.pdf

Looking at that it appears that the //c uses 16 4164 type DRAM chips.  They're labeled 6664 on the schematic which is I believe from googling it a Motorola part #, Most //c I've seen used another brand of chip though, most often Micron Technology (MT).  Unfortunately MT chips have a reputation for going bad over time.  I've also seen TI, Hitachi and other brands in Apple products of that era, so who knows what you actually have.  But in general I think if you order 4164 from a reputable source like JameCo you should be OK.

https://www.jameco.com/z/4164-150-Major-Brands-IC-4164-150-DRAM-65-536-Bit-65-536x1-150ns-with-Page-Mode-DIP-16_41662.html

I think the 150ns parts are fast enough for a //c but look at your chips and match the speed if possible, especially if you aren't replacing all of them.

Unfortunately your DRAM chips are probably soldered down, which makes replacing more work.  And work that has to be done carefully and correctly to avoid damaging yuor motherboard.  Definitely don't solder in new chips.  Use a quality socket like the round hole machined ones.

If you can determine which chips are bad, you can replace just those, but you may end up replacing more later.  Often if one or two fail, others are on their way.  To be on the safe side I always order at least a few extra ones.

softwarejanitor wrote:...uses 16 4164 type DRAM chips

FYI - While the original //c motherbioard uses 4164 chips, later versions use 4 41464 (65K x 64 bit) chips.

jeffmazur wrote:

 

softwarejanitor wrote:...uses 16 4164 type DRAM chips

FYI - While the original //c motherbioard uses 4164 chips, later versions use 4 41464 (65K x 64 bit) chips.

Duly noted...  I've never actually owned a //c.  I guess the ones I've seen opened was the earlier style motherboard.    The later one would be a lot fewer chips to replace.  I'd definitely just replace all four with sockets on that one I think.

You will probably want to upgrade to a newer ROM version than 255.  That old of a mobo probably is 16 4164 chips.  JameCo is reputable.  You could try Aliexpress or eBay but its more risky.  May be a bit cheaper.  Not much you can do about shipping and crazy European customs charges and taxes though.  CVT may know somewhere that might have them over there.  Shipping from California where JameCo is to Texas is high enough, and we're ostensibly in the same country.

Giano wrote:

So far I haven't found any alternative shop located in Europe, and Aliexpress is a no go for me. 

I've ordered from Jameco the chips and low profile socketes too. Postage rates are reasonable: $16. But of course, custom fees will cost around $25 :-)

I've already ordered the ROM4X - it will be needed anyway to help me to locate the defective RAM chips.

Not sure where you are in Europe, but ТМС4164 chips are very easy to find and lots of shops sell them. Here are a couple:

https://shop.tvsat.com.pl/pl/p/5szt-TMS4164-20-64KBit-DRAM-IC-DIP16-RFT/13417

https://elextra.dk/komponenter/integrede-kredse/hukommelses-ic/tms4164-15nl-65536-bit-dynamic-random-access-memory/H29754

"ZP" means zeropage, the first 256 bytes of the memory, which are especially important for the 6502. "RAM ZP" means the issue already affects the first 256 bytes of memory. Just "RAM" means the test of the zeropage was successful, however testing RAM failed anyway.

Giano wrote:

Next step for me is to learn how to solder correctly :-)

In this case you will actually need to learn how to desolder first - which is the tricky part... :)

In post #11, 'MacFly' wrote:

" In this case you will actually need to learn how to desolder first - which is the tricky part... "

Uncle Bernie thinks it is not "tricky" at all:

You only have two options to desolder an IC from a double sided, thru-hole PCB which do not damage the PCB:

1. Use a professional desoldering station with a hollow tip soldering iron and an electrical vacuum pump. These are expensive (I have one which served me well for 40+ years)

2. Use fine tip wire cutter tool (like the blue one in the following photo) and snip off all the leads near the body of the IC. Once the IC is body is out, you can then use a fine tool (like the needle nose pliers or the tweezers on the photo) to grab the pins still stitting in the PCB one by one, heat them with a normal soldering iron, and pull them out. After that, solder each hole shut so it has a small solder "dome" - use leaded solder, if possible. Then use fluxed (but not activated) braided solder wick on each hole: place the solder wick over the hole and heat up the solder wick by touching it in the location over the hole with a soldering iron. "Screwdriver" type tips on a 60W temperature controlled soldering iron work best for that step. The solder wick will suck all the solder out of the hole. Then it is ready to solder an IC socket in.

DO NOT USE any of these spring loaded suction "Desoldering" tools, ever. If you have one, throw it in the trash. The reason is they they have a fierce recoil and this damages the traces on the PCB more often than not.  These tools are worthless but look like a good idea. The makers of these tools knew about the problem and so they once made some which had counteracting, balanced mass pistons inside. Hence, no recoil, and no damage to the PCB. But these were patented, very expensive, and rare. All the ones you can buy today are the primitive type with the recoil and the risk of PCB trace damage.

The reason why is recommend leaded solder is that it has a lower melting point and better flow characteristics than the dreaded lead free solder to push nowadays. Which in the end is a massive scam and ripoff because lead free soldered electronics have reliability issues and don't last as long as the ones soldered in the traditional way using leaded solder. There is a reason why leaded solder is still legal to use in certain applications. But for the consumer, nooooo. Stupid consumer / slave / human lifestock shall buy a new car or a household appliance after a few years when the lead free solder joints have developed micro cracks or tin whiskers. This is why it's a ripoff. Instead of banning leaded solder they should have provided proper recycling streams for electronics which reclaim all the valuable metals in them. In typical electronics junk there is more gold, silver, tin, copper per weight than in some inferior ores mined nowadays - the good ore deposits are long gone in many places. So 100% recyling of electronics would make sense. But they throw it into landfills. Maybe future generations will mine the landfills for metals, who knows.

- Uncle Bernie

Some tools every electronics hobbyist needs:

Required Tools.jpg

Uncle Bernie's method of clipping out the chip with a small side-cutter (the green handled tool in his photo) is a good idea.  

As he also noted, those spring-loaded solder suckers are not a good idea, not because they damage the PCB traces (I've never done that in 30 years) but because they're not the best at removing sufficient solder from the hole to be able to remove the chip.  So that prompts you to keep heating the area with the soldering iron and trying over and over again...THAT is what damages the PCB.

baldrick wrote:

Uncle Bernie's method of clipping out the chip with a small side-cutter (the green handled tool in his photo) is a good idea.  

 

As he also noted, those spring-loaded solder suckers are not a good idea, not because they damage the PCB traces (I've never done that in 30 years) but because they're not the best at removing sufficient solder from the hole to be able to remove

I also use the method Uncle Bernie mentions of clipping all the pins and them removing them one at a time.  I've worked at places that had an actual desoldering/rework station so I know what I am missing not having one at home.  Someday it is on my list.  Next purchase is probably an oscilloscope.  But this desoldering station is one I've been looking at.  It is made by the same company that made the soldering station I use and I've been reasonably happy with it considering it wasn't that expernsive.

https://www.amazon.com/YIHUA-Desoldering-Variable-Temperature-Function/dp/B08BK69H2M/ref=sr_1_32_sspa?crid=1SFVJHM3HLYMW

@softwarejanitor, that looks like a reasonably priced unit.  Do be careful with overheating the pad with that type of tip.  The mass at the tip looks pretty significant.

I've been using the Pace SODR-X-TRACTOR unit with the Sensa-Temp Power unit (self contained) which does a great job, BUT  (as stated) the price of these units are quite high in comparrison.

I run mine at 750 degrees for best results.

I bought mine piecemeal on eBay and aquired the 2 piece unit for under $200.  One thing I would sugest for those who pursue this specific model is to add a one-way valve (shown below) to the vacuum line because the vacuum pump has a tendency to push a small pulse of positive pressure before the vacuum kicks in.  I found that to be quite annoying.  The thing I like about this model is the tip.  It's long enough to allow you to see what you're doing and hot enough to desolder pretty-much anything -but there are cases where I have to use my hot pencil to melt large ground-plane connections. (because the heat sinking is too great)

The downside of this desoldering unit is the glass tube.  They're made of Borosilicate glass and are quite fragile.  I discovered this when extracting the filter and splash guard (within the glass tube) with a pair of needle-nosed pliers.  If you know in advance to NOT  remove the internals for cleaning using metal tools, you will save yourself some coin.  Take note of this with any Solder extractor that uses glass tube collectors.

Pace Sodr-X-Tractor.png

Here's a photo of my home soldering station. (excuse the mess!)  I guess I take my soldering a little too seriously LOL!

From Left to right:  Weller hot air station ...  Pace Desoldering unit (handle shown above) ...  Weller Dual soldering station (one tip medium, one tip fine point) ... XYtronic Auto temp (set for high temp) large tip soldering pencil.

FYI, I never use a wet sponge to clean my soldering tips. (even though it's shown below)  I suggest using a dry folded paper towel.  Just as effective and doesn't cool the tip.

Solder Station.jpg