Alternative parts : New SRAM for C64C Short Boards

I've fixed quite a few C64C short boards now and nearly all of them have had bad RAM.  On Ebay the RAM for C64C's seems to be at a premium.  I got a great deal buying a RAM expansion board for a laptop with lots of socketed chips but was there a better alternate.

It turns out there is with Jamarju's c64-sram, SRAM substitute for C64C shortboards

So off to PCBway I went and grabbed some boards to test it out.

There aren't too many parts to this project which made it pretty simple to get going.  Probably the hardest bit was just getting the chips aligned on the pads.  After that I found if I was really careful I could just apply some flux and then very carefully drag solder down without tacking the corner pins first ( If it's your first time you should tack with chip down first to stop it moving ).

Although I did get a few bridges a bit more flux and some solder wick made clean up a breeze.

You can see in the middle the New vs the Old RAM.

  

My C64C boards nearly all have socket RAM now so I popped them out and jammed the board in and it worked first time. I quickly built a second one and that worked too.  I'm pretty happy about this project, a big thank you to Jamarju for sharing.

Maintenance : Recapping my Amiga 600's

Some time ago I bought some Amiga 600's.  Both were sold as not working.  One was actually completely fine, the seller didn't investigate it properly.  One has a memory fault which was fixed by bypassing a bit of corrosion on the board. However both of them are showing signs of leakage on the surface mount capacitors.  I've been putting it off but now I really need to do something before any real damage is done.

Firstly . . . STOP!

There are some little square metal cans on the board . . . don't get cleaning fluid / isopropyl anywhere near them . . . or you may be surface mounting a new composite video chip on your board.

More on this later.

Do your research / Buy the right tools

I've been looking at this for ages and I've watch twist methods, cut methods, solder iron wiggle methods and finally hot air rework methods.  The only one that appealed to me was the last one.  I didn't have a hot air rework station yet so I set about trying to find a good one.  I looked at the ridiculously cheap Atten right up to the Hakko, but in the end I got a Quick 861DW as recommended by Louise Rossman and later reviewed by Dave Jones.

I'm glad I did, using it made getting the SMD Caps off an absolute breeze.

Now putting back the Caps that was an issue.  Pretty much every video I watched only showed the Caps coming off.  No one actually showed them going back on.  This sort of concerned me as people showed everything up to putting the new Caps on and then bang, they were done.

I did experiment on a practice board putting on the Caps with the Quick, but I really didn't get the result I wanted ( probably due to total inexperience ).  I did however have much better success with leaded solder paste and a soldering iron. I saw this in only one video I watched, so thanks to that guy for showing the process.

Where to start?

I started with the two caps right in the middle of the board, there were no components or connectors near them and so it was a good place to get my eye in.  I held the Cap with some tweezers while I slowly move the heating element side to side.  I found I only really needed the air on about 1/3 of the maximum and kept the temp at around 250.  The Caps popped off really easily.

I did find I used too much paste for the first two.  For the next three caps near the floppy connector I used less paste and flux which made a massive difference.

You'll probably notice that I am using the solid electrolyte capacitors from Retro Bench in the photos I did look at pricing buying these myself but it ended up being cheaper to get the kits from them for just doing my two 600's.

Doing the hard bits

There were two areas of the board that I thought were going to be really hard. Between the keyboard connector and the sound jacks and the cluster under the RF modulator.

I decided to tackle the keyboard caps first, I was planning on taking the jacks off but after removing the RF modulator ( and the trouble I had with it ). I decided just to try the Kapton tape.  I removed the top of the keyboard connector first and stuck on the Kapton tape.  I then quickly used the Heat gun to remove both of the Caps.  I then soldered the Cap nearest the white jack first and then the red using a really find solder tip.  In the end it turned out great.

 I am up to the RF modulator and the cluster of caps underneath it basically made this operation really difficult without removing it.  I was going to get rid of it anyhow as I wanted to put HDMI/VGA into this Amiga 600.  I watched a video by Ms Mad Lemon who had a great tip on removing it.  Unsolder the small pins, then unsolder the big pin at the edge of the board, then wedge something underneath and slowly push the other pins through with the iron.

 

I sort of did this.  I removed the small pins solder with my desoldering gun.  I used solder wick and lots of flux to remove as much solder as I could from all of the big pins and worked hard on the big edge pin until it was clean.  Then I used a plastic spudger to help lever the modulator off while using the iron to melt and push through the remaining two pins.

Here we go with the last Caps.  Hopefully it's all working once I get them on.

So I go the new caps on and it works perfectly via RGBI.

Except . . . go read these links . . .

http://www.waveguide.se/?article=amiga-600-video-encoder-upgrade
 
https://www.ikod.se/z221-z222-fix/

https://www.ikod.se/cxa2075m/

 Take home tips

Use tweezers and a hot air rework station to remove the caps.  Not too hot and a medium airflow.

Use small amounts of leaded solder paste and flux to get a good join.
Use Kapton tape to protect plastic bits
Remove the top of the keyboard connector to get some more clearance.
Use solder wick and desoldering guns to remove solder from through hole components
Use plastic spudgers to apply leverage
Remove the RF modulator to get clearance ( chances are you'll never use it again so leave it off ).

** WARNING DO THIS REALLY CAREFULLY ** 

Use solder wick to clean the pads then give it a good clean with isopropyl alcohol.
with a small amount on a cotton bud. Clean up with isopropyl after soldering.

Keep all fluids away from the 221 and 222 metal cans or you will damage them.

If you do damage them . . . well . . . read my blog entry on fixing the Amiga Video.

 

Repair : C64 Black screen with signal : bare board

So I've been looking for a challenging board on Ebay as it's pretty much the only place available for me to find dead C64's.  They are expensive and in general not difficult to fix.  The board I fixed first up was a really dead Gumtree purchase.

Anyhow on with this new board.

1) The Power on flicker

When I first turned the board on I got the "power on" flicker.  This was a really good sign.
The SID on this board is soldered on the board so I'm pretty hopeful it's working at this point.

2)  Dead Test Cart.

Plugging in the Dead test cart I got the black then white flashing screen.  This is a sure sign that one of the RAM chips is dead.

I felt each chip on the board and one of the RAM chips was boiling so I pulled it and put a known good one in.

On turning the machine back on it was still flashing, this was a sure sign that both RAM chips were dead.

I replaced the second one and straight away I got the Basic screen.

3) Jiffy Dos Dead?

The Jiffy DOS screen only stayed up for 5 seconds, then the cursor stopped flashing and then the screen cleared.  I had a spare kernal on hand ( that I had burnt in a previous project ) so I swapped it in and ever since it has been rock solid.

Finale!

Well that was easy, two ram chips, one kernal rom and everything is working, even the SID.

So I'm thinking I am done with C64's . . .

I'm thinking about trying to pickup some dead Amiga 500's as I'm getting a little bored of easy to fix projects.

Alternative parts : Replacing SID with a SwinSID ( and building one )

I've been fascinated for years with the original attempt to replicate the SID, the SwinSID.  I've always wanted to build one but I found my lack of knowledge of electronics and lack of detailed step by step instructions on Swinkels website was quite a stumbling block for me.

Years later and with quite a few electronics projects under my belt, this little gem from Tolaemon appeared in my search while trolling around the myriad of shared projects at PCBWAY.

Tolaemon's nano SwinSIDb tutorial . . .

And so before I even went to website I ordered the PCB from PCBWAY

I must admit I was a little worried that this wouldn't work but hey I'm giving everything interesting a go that I can and here is what I ended up with.  After soldering MiSTer I/O boards and SDRAM boards this project proved to be a very easy build.

The version of the Microchip software I used was a little newer than that used in the tutorial and it was here that I became unstuck.

I burnt the firmware fine and the lockbits but when it came to the fuses all of the options had been renamed.  I left everything default and selected the correct external clock setting (EXTCLK_6CK_14CK_65MS) and burnt it to the chip.

Putting the SwinSID in the c64 I got a horrible horrible tone that didn't change.  The good thing is when you go to re-program the chip you can re-read the settings and for some reason the external clock hadn't changed from the default.

So I changed it and burnt it again and this time there was silence when the power went on.  On loading a game I found it would make a little noise then silence then some more noise but was nothing close to the music I expected.

Again I put the chip back on the programmer and one of the fuses that was default on needed to be turned off ( the CKDIV8 ).

This time I got success!!!

So what do I think about the SwinSID . . . well it's actually pretty good, the project was a lot of fun and I learnt quite a bit doing it.  For my C64's however I think I'll stick to the ARMSID as my SID replacement of choice.

I found the SwinSID did pretty well on the games I tried, but it just sounded a little off in some places also for ShadowFire it just didn't work at all.

Alternative parts: Replacing 6526 with 8520 cia

I found it hard to find 6526 CIAs to replace the dead ones in my C64s.  Scouring the the Internet hoping for an alternate I found this Forum discussion about using an Amiga 8520 CIA instead and what was different between the two chips. As 8520 chips are abundant on AliExpress I thought I'd give it a crack.

For the most part they work pretty well. Ive found some weirdness with my Ultimate 64 cart where the auto run doesn’t work, but mounting and loading normally is fine.  I wonder if it’s the clock?

Overall they seem like a good substitute until someone builds a better one.