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.

Enhancement : Gonbes VGA upscaling

Gonbes 8220 and C128 RGBI

I have quite a number of C64's, C128's and Amigas, but I only have one proper monitor.
New TV's really don't really work very well so off to the inter webs I went.

I've been looking at heaps of projects for RGBI conversion for the C128.  None really took my fancy until I saw this one from Mattis Lind, it was small, it was compact and it was surface mount.

• https://github.com/MattisLind/CGA-RGBI-to-Analog-RGB

The only thing I didn't like about it was the connections.  I'd rather have them on board than solder wires on to the board.  Luckily it's opensource and the Tool Mattis used was probably the easiest PCB design tool I've ever tried ( I've given up on every other one ).

So I added in some bits including mounting holes. I did make one mistake and that was to break the ground.  I used a jumper to fix that with the original holes for the wires that I left in place.

 As you can see the over all result was really neat with all of the colours displaying nicely.

Gonbes 8220 and Amiga RGB

I also wanted to get my Amiga's working nicely on a monitor too and not the TV I was using.  The colours were really washed out.  The pin out on my Amiga monitor cable was not compatible with the RGBI board.  However I was able to use it a as template to build a nice connector to the Gonbes unit on a bare RBGI card PCB ( note it's just point to point wires and a resistor, nothing else ).

Details for the hook up came from this link

• https://ianstedman.wordpress.com/2015/01/25/gbs-82xx-experiments-part-2/

Which I found under this video

• https://www.youtube.com/watch?v=xqlrOcGZx38

 As you can see the results are pretty good.  

(The monitor I used to test was really crappy)

 

Comparing the Amiga Board to the C128 Board.

Repair : C128 PSU working ( but was DOA ).

I've done a lot of reading about how crap the Epoxy filled c64 power supplies are ( do not use them, put them in the bin ).  Everyone however seems to agree that the c128 power supplies are great and worth using.  I never got a power supply with either of my c128 so I thought I'd get one.

Off to Ebay I go and get a "working" unit . . . yeah right.  When it arrives it's totally dead.  I have a look inside and the Caps have leaked and one of the fuses is in parts.  On further inspection BOTH fuses have not survived the bumpy ride to Northern Australia and to add to that the 1.4A fuse was only 1A . . . Hmmm . . .

That's cool, I can fix this and I was planning on re-capping it anyhow.

Here is the unit after I gave it a first initial clean and flushed the entire board.

You can still see some gunk around the 4th diode and where the resistor and the two wires join.  I used a desoldering gun to remove both of the caps and then used an interdental brush to make sure it was all as clean as possible before flushing the board again.

Desoldering guns are awesome, so after 5 seconds the Old caps are out and the New ones are in.
They are not exactly the same voltage spec, but the uF is exact.  You can go higher with the voltage without an issue ( just don't go lower ).  They are also good quality Panasonic ones.  Don't buy cheap caps.

 

Back it all goes into the case, I'm not turning this on until everything is in it's correct place.

During transport this tab broke off.  A little Tamiya liquid cement and you can't even tell it was broken.

At this point I've taken it outside and plugged it in with extra an extra RCD just to make sure the magic smoke didn't escape.  After a good run I tested the voltages, which ended up being 10V AC and 4.9V DC.  I'm pretty happy with that so on to the final phase.

 

 Plugging it into my secondary C128 and hey presto.

There's only one thing to do now and that's to replace the plug with so I don't need a travel adapter.

Repair : Amiga 600 for parts, not working ( corroded trace )

Due to my geographic location, local population and transient demographics it is really difficult to get reasonably priced Amiga kit.  Working Amigas are like gold.  So the cheapest solution I have is unfortunately Ebay and "For parts, Not working".

So far I have bought two "For parts, not working" Amiga 600's.

Amiga 600 number 1

The first Amiga I got came all the way from the UK,  It was grubby but overall it was in good condition.  Opening the case it was clean, the caps have not leaked ( yet! ) and it looked in really good shape overall on first inspection.

Powering it up told a completely different story.  The screen flashed from grey to green.  I hit up Google and found this wonderful resource.

http://wiki.classicamiga.com/Amiga_boot_error_code_colours

Seems like I had an error in the Chip Ram.  Initially I thought I'd have to recap it first, but then I noticed a little fuzzy blue coloured dot near the RAM.

One of the traces to the RAM had corroded into a blue copper oxide puff ball.  I cleaned it with some Isocol and a cotton bud and found the trace has completely disappeared.  Using a multi-meter I tested all of the surrounding traces and found only one was broken.

A little soldering and some wire and hey presto, a fully functional Amiga 600.

Update : the other corroded trace also finally gave up so I've bypassed that one as well.  It was pretty bad before I cleaned it up.  This time I scraped all of the bad traces off of the PCB.

Repair : 1571 Power supply issues

When I bought my C128s I really wanted to get the floppy drive that was designed for it.  So I bought a 1571.  Like most retro gear it was sold as working, but there were . . . problems.

The drive would power up but not stay on once the disk was being accessed and it would reset.  The problem was obvious bad power supply.

Back to Google I go and I found the wonderful blog World of Jani with what I needed.

http://blog.worldofjani.com/?p=2131

I wasn't too keen on the original bare power supply or trying to fix it.  I wasn't able to get that model mentioned in Jani's blog either.  In the end I picked up another caged Mean Well power supply from RS components and set to work.

STOP . . . These voltages will, KILL YOU . . . STOP

I don't recommend doing this at all, mains voltage is really dangerous.
Get someone qualified to do it for you.

This is the unit I ended up ordering and installing :

https://au.rs-online.com/web/p/embedded-switch-mode-power-supplies-smps/6447073/?sra=pstk

Now I have a beautifully functional 1571.