Repair : C64 No signal, black screen fix - part 3 - the final chapter, success!

Well . . . I was totally wrong about the ROM's I replaced both to no effect.

Back to the drawing board.

Looking at diagnostic pictures and my remaining socketed chips I was getting down to a last man standing situation.

I only had 5 chips left, CPU, CIA2, PLA, Color Ram and two identical logic chips.

PLA - ease don't

I guessed the PLA ( I had two spare ) and got to work de-soldering it very, very carefully
WARNING : apparently it is very easy to kill it by removing it.

I eventually got it out very cleanly.  I put in a socket and then inserted a new PLA and got this.

Ugh Oh,  that's not right. I put the original PLA back in the socked and got the same picture. I pulled out the multi-meter and began checking all of the connections, nope everything was fine.  I then checked for shorts.  I already knew that two of the pins short when a cart is attached so I removed it.  I quickly found the short between two pins connected to the Colour RAM.  The solder had joined under the socket.  With a piece of copper solder wick I jammed it against the side of the socket and it cleared the short and I went back to the black screen.

The Final Culprit - CIA2

Time to pull CIA2.  So I got to work and removed it and powered it up without CIA2.

Now we are getting somewhere.  I quickly socketed it and jammed in my two spare good CIA's.

Now it's all working . . . so what was the damage?

I replaced 3 x logic chips ( status unknown, one was probably dead ).

1 x ram chip ( dead ), 2 x CIA chips ( dead ), 1 x SID ( dead ), 1 x 8701 ( dead )

Was it worth the repair.  Cost wise I'd have to say no.  If you wanted to have C64 that works just buy a working one.

Education wise, yes it was a great exercise. On the plus side I now have a test board with almost all of the IC's socketed.  I buy this dead stuff to learn skills and my through hole soldering is so much better now.

I'm also pretty pleased I got the PLA out in one piece.  I've read it's quiet hard to do without killing it.

Burning C64 ROMs ( part 1 ) : Kernel ROMs

I've always wanted to try to burn new EPROMS for my C64.  I remember as a kid pulling apart my carts and pretending I could mod all sorts of stuff into them.  Well now I can . . . sort of.

As part of my trouble shooting it looked like the Kernel/Basic ROM was shot so I thought I'd have a go at burning one.  Turns out it's actually pretty easy with the right equipment (It also turned out the Kernel ROM on the board was fine after all).

I bought myself a "TL866 II plus" and some 27128 EPROMS from Ebay.

This site has the C64 ROM images and which EPROMS are compatible:
https://ist.uwaterloo.ca/~schepers/roms.html

The UV Erasable ROMs I got were actually ST27c128 which the software didn't have an entry for, but I read on the internet that if you just use the AMD AM27C128 and turn off the "Check ID" it works fine, and it does.

Read part 2 ==>

Alternative parts : Replacing the 8701 with TOLB

As part of the Black Screen repair I had discovered that the 8701 timer was bad.  There was not video signal coming out of the c64 at all.  With a swap of a good 8701 it was confirmed, but in the end I needed a new 8701.

So I bought a couple of TOLB (pal) from Eslapion and they've just arrived from Canada so in they go!!
https://www.ebay.com.au/usr/eslapion

They work really well.  He sells two versions one for PAL and one for NTSC and he sells a PLA replacement as well for older c64's ( not my c64c's which have a much bigger PLA with more integrated logic ).

Repair : C64 No signal, black screen fix - part 2

Who's the suspect?

So at this point I was stuck.  I scoured and read every bit of Ray Carlsons C64C chip notes.
http://personalpages.tds.net/~rcarlsen/cbm.html

I'd looked at every single picture of the C64 pictorial fault guide.
https://derbian.webs.com/c64diag/

The only cart I had that sort of worked was my dead test cart.

But then I had a flash of inspiration.

Ultimate II 1541

Now I mentioned Gideon's Ultimate 64 in part 1 of this article.  However I also had an Ultimate II 1541.  Initially I wanted to use it to make sure the disk test I had done with the 1571 was okay.

When I plugged the cart in and turned it on . . . nothing.  The disk light flashed but the screen was black, but then something great happened.  When I brought the menu up with the middle button on the cart I got this!

Looking at it I could make out where the menu text was meant to be.  There was a lot of junk on the screen but I could definitely see the menu.

 

The Kernel is a bit iffy

Looking back at the Ray's site and the Fault guide, everything started pointing to a Kernel Fault.  This also made sense as the Kernel and Basic ROM are on the same chip.  So when I returned back to Basic I'd get a black screen, but then when I went back to the Cart menu, it didn't use basic.

So it's definitely the Kernel Basic Rom and probably the Character Rom too.

I didn't have anything that could replace the Kernel Rom, OR DID I!!!  One of the great things you can do with the Ultimate II is to use a replacement Kernel Rom and VOILA!!  When I return back to basic I get nothing, but that's to be expected as the Cart can not replace the Basic or the Character Roms.

Slow boat from China . . .

At this point I'm waiting for some EPROMs and a Burner to come from AliExpress and for some replacement parts from Ebay . . . so stay tuned.

Repair : C64 No signal, black screen fix - part 1

 So as I’ve mentioned previously, I’ve bought a whole stack of not working C64’s from the net.  Mostly they’ve worked or needed minor work to get them going. This one however was dead as a door nail.

I actually gutted it to house my Ultimate 64 from Gideon, if you haven’t seen or bought his stuff you’re missing out. https://ultimate64.com/

This was actually one of the first c64s I bought for my C64C revival so I just put it away as I had no clue how to fix it.

No now some two years later I thought I’d give it a crack. So here is my adventure.

Oh SID where art thou ( status : dead )

I’d already discovered that the SID was bad when putting it into my Ultimate 64. It ran red hot and just didn’t work.  So I just left it off of the board as according to Ray Carlson’s website it can cause black screen if dead.

No signal, no picture

When I turned the computer on there was no signal at all,  the power light came on and the fuse was fine.

The 8701 timer ( status : dead )

My first step was to switch out the 8701,  I have a working c64 and luckily the chip was socketed on the both of them. When I turned it on again I got a Pal signal detected on the TV, but it was now a proper black screen, progress.  The next thing I did was order a replacement, but more modern TOLB from Ebay.

Old single sided sockets are crap

Unfortunately when I put the chip back in the working C64 it stopped working.  It turned out the socket was bad. So the first thing I did was replace those sockets.

Pulling out a CIA ( status : unknown )

The next item on my agenda was to pull the only socketed CIA on the board (near the keyboard connector).  It made no difference, but I left if off because I could not test it and I could not swap it.

Swapping the VIC II ( status : good )

Again I was lucky that both VIC II's were socketed so I swapped it into my good board and it was all good.

Swapping the RAM chips ( status : unknown, probably good ).

The two RAM chips where socketed. I had bought some replacements but didn't know if the worked.  Swapping them made no difference.

Ugh Oh, no more socketed chips!

At this point I had no more chips I could easily swap so I decided to remove and socket the replaceable readily available logic chips that I had on hand and this is where I can unstuck.  Although I had had no trouble removing the sockets, removing the IC's using my desoldering gun proved to be a total pain.

I removed the 74LS14 first,  solder came away nicely but it wouldn't budge.  In the end I cut the legs off and pushed them through with the soldering iron.

I removed the 74LS08 second, it was much easier this time, practice you know. and I only cut a couple of legs off and the chip fell out.

At this point the C64 started to show some life, when I flicked the switch I'd occasionally get a flask of colour or with the dead test Cart in I even saw it working in the total mess of characters. Then it'd die and reset.  But I got nothing with no Cart in.

Lastly I replaced the SN7406 Hex Inverter, I finally discovered how to desolder properly using my gun.  Put the nozzle over the pin for 2-3 seconds, then swirl it around so you feel the pin loose. Then pull the trigger.  Once I removed all the solder I grabbed the chip with pliers and instead of pulling it I gave it a slight twist to show where I'd missed solder.  I went back to those pins and it fell out intact.

I found after this I got an occasional black and with flashing screen which would stop with the dead test Cart in and every now and then the border and background only would appear in the colours of the dead test cart.

 

What now? I've go no more chips!

At this point I was stuck, I'd order some chips but I had nothing more on hand . . . or did I.  I decided I'd recap the electrolytic capacitors.  The result being that I started getting the flashing more often when I turned it on, with far less power cycles.  From my IC extraction adventures I was an old hand now and they all fell out first go, which was really nice.

Winning!!

 

Does my 1571 reset on power cycle and can I load a disk typing blind.

I plugged my 1571 into the board and the missing CIA chip and a keyboard as I wanted to test that the SN7406 was okay and also to see if could get the drive to do a directory listing.  Resetting the computer also reset the 1571, but sadly no bananas with loading a disk.

Repair : Bad C64 Colour RAM

One of my first C64C Ebay purchases was a complete "working" C64C with a 1541II and a number of games.

When I got it, it was great but it just looked washed out.  It wasn't until I tried a few more games that I realized that something was actually wrong.

. . .

To the Internet

. . .

Everything we need these days is a quick search on Google.  I found two fantastic site right away.

Ray Carlsen's amazing website : http://personalpages.tds.net/~rcarlsen/

Pictorial C64 Fault Guide website : https://derbian.webs.com/c64diag/

The first thing I did was order a C64 power supply from Ray.  I really did not want to damage my C64 any further.

The second thing I did was buy a cheap desoldering gun and some DIP sockets.  Get the right tools and do it right the first time.

The last thing I did was get a couple of colour RAM chips.

. . .

So the process was pretty simple.

Add a little solder and use the desoldering gun to free all of the pins
Use some solder wick to remove the remaining solder with your soldering iron.
Solder on a DIP socket ( always put in a socket . . . always ).
Push the chip in.

Behold . . . real colour . . .