Finding, repairing, and enhancing a Commodore C1901

My friends often tell my that I'm often lucky to stumble upon cool stuff that other people have trashed. And, hmmm, well maybe I actually am };-P.

This day I was out walking with my daugther (age 8years) and I had my youngest son (age 1½years) in the pram. Suddenly in the corner of my eye I saw the well known Commodore C= logo at the other side of the street. I rushed to see what it was; a lot with a C128, C1901 monitor, and some smaller stuff. As it was raining a bit, I didn't get a close look at it, just stuffed the things under the pram and took the monitor in hand. Steering the pram with one hand, holding the monitor in the other, I began the trip home.
When I got home, I had a closer look at my loot.

But, as you've properly noticed from the photos, the people who'd thrown these goodies away, had been so 'kind' as to cut all the wires they could find before trashing the lot };-S

Well first thing to do, was to let the whole lot rest in my nice warm basement for a couple of weeks in order to dry it up. After that, I decided on having a closer look at the monitor to see if it was alive. As the power cord had been cut by the former owner, I fitted a power plug I had from and old defect ATX-PSU. The hole in back casing was already prepared; it was only a matter of cutting the plastic bit out with a Stanley knife.

I connected a power cord and pushed the switch. I heard the well-known sound of a degaussing circuit and the high frequent noise from the tube powering up };-P But then there was a loud POOOF, then a loud hissing noise, and then white smelly smoke began to emerge from the insides of the monitor. ARGH! Quickly I pulled the plug, and the smoke stopped emerging. PHEW! I did this testing in the evening in my workshop in the basement; and my workshop happens to be just next door to our bedroom. I was NOT the popular husband that night, as the smoke was extremely smelly; a bit like rotten fish mixed with the smell of old fart };-S

Hmmm, the next day I had a closer look inside the monitor to see if I could find the source of the white smoke. But nothing was obvious... I had to try and apply power again! To avoid getting a divorce attorney on my back, I did the testing outside this time.

...but to my suprise, no smoking and no hissing from the monitor?! The bright light outside did however help me get a good look inside. And near the front of the monitor, I found this little felow.

By googling a bit, I found out, that this is what is known as a so called safety capacitor. I don't really know what it is there fore, but it was obviously toasted. So I desoldered the poor thing.

In the defective ATX-PSU mentioned earlier, I found this little guy with the same specs, as the one I've just removed from the monitor.

So onto the chassis PCB it went.

Now there was no hissing or smoking anymore };-P Time to see if the monitor actually worked. I googled that the inputs was digital RGB (used by the C128) and composite. So I hooked up my Amiga A600 through it's built-in composite module and got this

Hmmm, no colours?! This looked an awefull lot like a Commodore S-Video signal missing it's chroma input. Did a bit more googling, and found that this monitor model came in different flavours: With composite input, S-Video or both, but it seems like the chassis is the same on all these; you can just add the missing inputs. However my googling also led me to a blog runned by a guy calling himself JetSetSkippy. He had this awesome post, where he amongst other things, retrofits a C1901 with a SCART plug enabling it to be used with true analog RGB-input (15kHz) };-P This was almost too good to be true, so I found a SCART plug in the pile and started right away.

As Skippy also explains, this chassis is already prepared for a SCART plug (notice the 2 rows of holes in the PCB just below the D-Sub in the pic). But the crazy thing is, that the designers must have gotten something wrong; cause the holes are reversed so you can't just solder in a standard 90 degree angled SCART plug. Maby that is also why this monitor ended up not being shipped with a SCART plug?! Therefore I (like Skippy) soldered wires on all the pins of the plug and began the cumbersome task of soldering them onto the chassis.

Phew! All the wires had to fit in a really tight spot, but finally I pulled it through (look under the black ribbon cable).

The plug was then attached to the metal frame in the hole already there...

...and the plastic casing was cut.

And now for a test };-P I first attached the A600 via my homemade RGB-Scart adaptor and the result was fantastic.

Next I tried an arcade PCB (attached via my homemade SuperGun) with equally fabulous results.

All in all, I consider this a great success! And should any of you guys out there have an old C1901 in the attic, I strongly encourage you to fit it with a SCART plug. It gives a very clear and crips picture, and the chassis is all analog with lots of knops, dials, and switches to make adjustments with. So far it has been able to sync with everything I have feed it, so it's going to be my main test monitor when I do repairs from now on.

What an awesome finding on a rainy day };-P

Homemade 1MB Chip RAM Expansion for Amiga A600

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As regular readers might have noticed, I've in the process of pimping my Amiga A600HD at the moment. And now it's time to add some more Chip RAM. On Amiga Chip RAM aka Graphics RAM is the memory shared between the CPU and all the custom chips; hence the name "Chip RAM" };-P. A600HD is born with 1MB of Chip RAM installed, and back in the days that was a lot (twice as much as A500!!! };-O). However now-a-days, if you want to run games directly from the harddrive using WHDLoad, it's a little bit on the small side. The 68000 CPU can address up to 2MB, so it would be nice to add an extra 1MB to the pool };-P Now there are some commercial expansion cards that does that; the most popular atm being the A604 Memory Expansion. However it is imo a little expensive and also I really enjoy doing stuff like this myself.
So I started googling for DIY-projects expanding the amount of Chip RAM and quickly found this wonderful hack (now known as "The-A600-Piggyback-Hack") by Zetr0 in a sticky thread over at AmiBay; he piggybacks a DRAM IC on top of each of the 2 already fitted in the miggy. That in turn lead me to this blogpost by Victor Trucco (I ran it through google translate, as I can't read Brazilian Portuguese) via a link in the thread; he piggybacks 2 DRAMS on top of 1 of the already fitted DRAMs.
Now I had some great ideas to work from, however I wanted a solution that was easy to remove again, and also I wanted to give the project my own personal flavour };-P After reading the thread at AmiBay and inspecting the schematics for the A600, it was obvious that all the address-, data-, and control-signals needed for the extra Chip RAM are present at the trapdoor connector. So my plan was, to attach the 2 extra DRAM-Chips piggybacked together there. After doing some crude measuring, I found that the pitch between the pins in the trapdoor connector is the same as in a socket for PCI-card to fit in a PC.
I didn't have neither DRAM-chips nor PCI-sockets, so I went hunting on evilBay and quickly found a guy offering a lot of 10 Toshiba TC514260DJ-60 SOJ chips for a price of only $15.33 incl. shipping to Denmark. Next I found a lot of 5 PCI slots at a price of $7.41 incl. shipping.
I waited and waited, but finally both lots arrived in the mailbox };-P Now I had all the stuff needed; for wires I was going to use rainbow ribbon cable (having the same pitch as the pins on the DRAMs), as I just love how is looks like candy };-P

First I checked if my measures had been correct (I had just tried to match up the pins using an old PCI card). Luckily, it is a perfect match };-P

The first thing to do was to prepare for the "marriage" of the two DRAM ICs. Being of SOJ type, they have their pins bend underneath themself, kind'a like a dead spider. So the one to go on top, had to have the pins straightened. First you lift the pins carefully with a Stanley knife.

Then use a set of pliers to make each pin straight. Here's the final result.

One pin is bend upwards. That is the RAS (Row Access Strope); the only control-signal that is not the same for the two ICs.
Next our happy couple are pressed together and "married" (do I hear wedding bells? };-P).

After that's done it's time to cut them rainbow ribbons.

The longer blue wire is for RAS on the upper IC. Luckily the IC-pin just beside the the RAS is NC (non connected), so no harm is done using that for the upper ICs RAS.
First the pins 21-40 are soldered.

Next the pins 1-20.

Now all the wires must be soldered to the PCI socket

using these mappings:

And now for the big test (first I tested without the caps shown in the picture)

Now WorkBench found the new extra 1MB alright.

But when trying to use it, things got bad. The memory tester i use reported many random errors (random meaning not at the same addresses everytime) and when trying to load big games (like Cinemaware-stuff), I got random crashes.
At first I thought that this was a problem related to smoothening and/or decoupling, so I tried adding one 220nF capacitor across each supply to the ICs and one 2.2uF capacitor at each end of the powerrail for the ICs. That only made things worse...so removed the caps again. But now I still had as many errors as when they where still fitted. Grrrr!!!
Decided on giving the whole project a rest for a few days };-S

I made a post in the thread over at AmiBay and Zetr0 replied, that technically the solution looked fine. However he thought that caps might not be the way to go as they might induce more noise into the circuit than they'd remove. He also mentioned, that I might've toasted one or both the DRAMs and proposed that I either tried to test the two ICs individually or started all over with a new set of ICs.
I desoldered the IC couple and tried to divorce them, but it was not possible without destroying them completely. So in the bin they went. I made a new couple just as before and soldered them on the ribbons, but it ended out in one big mess. These ribbons are not meant for soldering in the first place, so the heat from soldering, desolering, and resoldering had made the insulation into one big pile of goo. So desoldered the new couple again.

I now decided on trying to use kynar instead of ribbons. They are much thinner and singlecore, making it much easier to control. However I was sad to give up on the ribbons, as they just look so cool };-(
Following an idea given to me by Phipscube (a dear personal friend and also an AmiBay member), I taped a piece of cardboard to the PCI socket and taped the ICs upside-down on it. I cut a hole in the cardboard for easy access to the lower pins of the socket when soldering. Then I started soldering the kynars one by one.

Again following a good advice from Phipscube, I did the soldering over a couple of nights in order to be fresh in the head...otherwise you end making a mess.

The really nice thing about kynar, is that it is so small and thin. However, the really annoying thing about kynar, is that it is so small and thin. Elgen

The final result looked like this.

Once again time for a test in Miss Miggy, but (MOAN!) I still had the frakkin' random errors! };-S
Tried to add caps, and again it just made things worse!!!
Now I was so close to giving up and trash the whole gorram project. However during the day, I came to think of good ol' Faraday and his cage. Hmmm, maby the instability was caused by electromagnetic radiation from either the near-by circuits, or maby just general radio-wave-noise. So after having tucked the kids in that night, I first wrapped the construction in paper to insulate

and then in tin foil (yup, the same kind I use for my kiddies school lunch };-P). I attached it in the trapdoor and connected the tin foil to ground. Aaaaand....

Heureka! The random errors had gone away! };-P

"Dad, did you put chips in my lunch pack for dessert?" "Sure did son, but not the potato kind };-P"

Now I had something that worked; it was time to make it look good too };-P
First I gently lifted the ICs from the cardboard using a Stanley knife. Then replaced the cardboard with a smaller piece that didn't have the hole in it.
Next I cut the PCI socket down to the same size as the connector in the trapdoor using Mr. Dremel and a small file. I then cut the end of the piece that I'd cut off, and superglued it to the end of the now smaller socket.

And now for a nicer Faraday cage.
Ever since I started doing electronic projects as a kid, I've always had this thing about having some tins in different sizes (from canned good) on my work bench. They often come in quite handy; as tabletop trashbins (for things that you might/might not need again later in the project); for small things (screws etc.) when you dismantle devices; for very hot solder when you clean the filter in you desoldering station; find more uses yourself };-P
Bottom line, I had this little fellow stading on the table that day.

I scraped a little bit in the paint and found that it was conductive and normal solder for electronics would bite on it. So I cut off both ends and cut the tube open using my Dremel.

(But perhaps I should've used a heavy duty disc instead of a normal one; the one on the right is a brand new disc };-P)

Next I cut out one big piece (top and bottom of the cage) and 2 smaller ones (the sides) using an old pair of scissors. I then bend the large piece and soldered the sides on leaving a hole for the socket.

As the last thing I soldered a wire from GND on the socket to the cage in order to ground it, and here it is in all it's glory:

And here fitted in Miss Miggy (and it still works };-P)

I wish to thank Zetr0 (AmiBay) for inspiration and good advice, Victor Trucco (blogger) for inspiration, and Phispcube aka Les (AmiBay and dear friend) for good advice and cheer-ups through many many txts often very late at nite };-P

Amiga A600 quick keyboard fix

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Since I've started working intensively on repairing, pimping, upgrading, etc. my Amiga A600HD, the keyboard has been acting up more and more. In the begining it migth fail self test every 10th boot or so (blinking CAPS LOCK and unresponsive), but slowly the frequency of fails rose, and here the other day it went totally crazy. It passed the self test alright, but most of the grey keys were unresponsive; including ENTER };-S

Ok, as opposed to the keyboard on A500, the one on A600 only consists of one big membrane with two contact points for each key. When a key is pressed, the contact points are shorted. Each key is an entry in a big matrix, and no logic is performed in the keyboard itself. The membrane continues into a flat cable with some sort of conducting compound at the end. The end then goes into a special flat-type molex-socket on the motherboard.

In order to be able to remove the cable from the motherboard, you must lift the upper part of the socket, as it works like a lock securing the cable from falling out.

Failing to remember to lift the lock before removing the cable, results in some of the conducting compound at the end, is beeing scraped off.

The reason for my keyboard malfunction is that I'm lazy };-S Often when I mess around inside miggy, I just place the upper part of the case vertically supported against something...WITHOUT disconnecting the keyboard cable. Often I accidently give the upper case a little push, and it falls on the floor, ripping the cable out of the locked socket.

The length of the piece of cable having the compound applied, is a bit longer than the socket (to be on the safe side I guess). So by cutting a little piece of the end with a normal pair of siccors, you get a fresh conducting piece to put into the socket.

Also I added a piece of normal transparent tape on the other side of the cable end, to make it sligthly thicker. That way the conducting compound is pressed harder against the contacts in the socket.

I fitted the cable in the socket again, and presto! Now it works flawlessly };-P