Commodore C16 Re-Cap and replacing the 7805 Voltage Regulator

 

Welcome to the first in a series of posts in which I am going to restore, repair and modify my Commodore C16.

As the C16 is a very old computer, it is always a good idea to replace the electrolytic capacitors due to the fact that they are components most likely to fail (with the exception of the TED chip) With age, they are prone to drying out or leaking and can cause a whole lot of damage when they do so.

                    

The C16 only has 8 electrolytic capacitors so this is a relatively quick job.

 

I decided to also replace the 1A 7805 with a 2A rated version of it (L78S05CV) as this has a bigger heatsink on it and will cope better with the high current draw of the C16.

A YouTube clip of the complete process from start to finish can be found at the end of this entry.

For this restoration you will need the following components:

 

1 X 1uF 50V Electrolytic Capacitor

6 X 10uF 25V Electrolytic Capacitors

1 X 47uF 16V Electrolytic Capacitor

1 X L78S05CV (2A) Voltage Regulator

Heatsink Compound

Solder

IPA Alcohol

 

Tools required:

Cutters

Pliers

Screwdriver

De Soldering tool

Solder Wick (advisable)

5mm spanner

Cotton Bud

 

Firstly we have to strip down the C16; This is the first time I have been inside this computer so this was just as much a learning curve for me as it hopefully is for you. I will highlight things which I found out along the way.

 

Remove the three main fixing screws on the underside of the C16.

Then open up the C16 as shown below

Remove the Power LED connector from the PCB; note that the Red wire is on the left as you look into the C16 from the front.

Then remove the long 20 pin Keyboard connector; I found that the best way was to wiggle it out from side to side but be careful not to bend the pin header pins on the PCB.

Remove the top of the C16 and then start removing the PCB screws.

 

There are 8 PCB screws in total, 6 of them are of the self tapping variety and are highlighted below.

And the other 2 are machine type screws which means that they are threaded (possibly M2.5) and are highlighted in the photo below.

After the PCB has been removed we need to take off the RF shield ; this is done by bending up the metal clips which hold it to on the component side of the PCB. I have highlighted their locations below.

I used a pair of cutters to gently lift up the metal clips; care should be taken if using cutters as it would be easy to actually cut the clip off.

Now we can start replacing the capacitors starting from left to right, I removed and replaced the capacitors one at a time.

 

The first Capacitor is C17 which is a 1uF 25V Electrolytic capacitor.

Below is the location of it on the component side of the PCB.

And below is the location of the vias we need to de-solder.

I used my de-soldering gun for the majority of this job but you could easily use a simple De Soldering tool instead.

After de-soldering, try and ease the capacitor out of the PCB. Care should be taken doing this as the vias have plated through holes which mean that there could still be solder in between the layers of the PCB.

 

I usually inspect the de-soldered vias before attempting to remove any component.

After my inspection I found that one of the legs still had solder connected to the PCB so I simply heated up the leg with my soldering iron and gently pushed it free from the solder. This was adequate enough to allow me to remove the capacitor.

Then carefully wiggle the capacitor out watching for any signs of physical resistance which would indicate that the capacitor was still soldered to the PCB.

 

Failure to ensure that the capacitor is completely solder free can and often leads to damaged traces on your circuit board; not the end of the world but awkward and fiddly to repair and also looks unsightly once done.

After that, we need to replace the old 1uF 50V capacitor with a new one.  It is vitally important that you place the capacitor in the circuit with the correct orientation. See the picture below to remind you.

The photo below shows a typical electrolytic capacitor with usual markings and meanings.

Place the 1uF capacitor as shown below and push it as flat on to the component side as it will readily go.

Turn the PCB upside down and bend the legs of the capacitor out to about 45°; this should ensure that the capacitor doesn’t fall down when soldering.

Then we have to solder the capacitor into the circuit. Good soldering practice is to heat both the component leg and via up for around 2-3 seconds using a hot soldering iron (I like to use leaded solder and a temperature of 330°C)

 

After both parts are warm enough to melt solder, feed the solder on to the via and leg once the solder has melted around the via and leg, remove the solder but keep the soldering iron on the joint.

 

What you are ideally looking for is the solder to rise up the leg of the capacitor until you get a curved surface all the way around the via and leg; this typically takes between 2-3 seconds.

 

After that, remove the soldering iron.

Once soldered, trim the excess legs of the capacitor away with a pair of cutters. You are looking to cut the leg just above the solder joint itself as if you cut into the solder you will weaken the solder joint.

Replacing the remaining capacitors is just a repeat of the instructions above however I did have some trouble removing a couple of capacitors which I will detail a wee bit further as we go through the capacitors.

The next capacitor to replace is C16 which is a 10uF 25V electrolytic capacitor; I had no trouble replacing this one so will simply show you the location of the capacitor and vias.

C18 another 10uF 25V capacitor was the next one to be replaced and again I had no trouble removing it.

C19 was next and that is another 10uF 25V capacitor.

Then I replaced C31, a 10uF 25V electrolytic capacitor.

C4 was next and another 10uF 25V capacitor.

The last of the 10uF capacitors gave me some trouble; C3 was very awkward to remove. Below is are the locations of the capacitor and vias to de-solder.

The first problem I had was when my de-soldering gun became blocked; below is a photo of me removing the blockage with the clearing tool which was the correct size for the nozzle.

But even after clearing the blockage, the de-soldering gum still failed to clear the solder from the via so I used my soldering iron to melt the solder on the effected via and gently pull the capacitor free from the circuit board.

Even after removing the capacitor using the technique described above, the via still had solder in it so I tried to use solder wick to draw the solder from the via.

Still no joy! So I tried to remove the solder from the component side using the solder wick.

But even that didn’t work! Time for some drastic measures.

I applied some fresh solder to the via.

Then used my trusty 20 year old solder sucker!

This did the trick; the via was now clear of solder.

After that it was a simple job of fitting the replacement 10uF capacitor, soldering and trimming the legs.

The last capacitor to replace is C3 which is a 47uF 16V electrolytic capacitor. And again this one gave me some problems. Below is the location of the capacitor and vias.

The main problem I had with it was the fact that the negative pin was soldered on to the ground plane and although my de-soldering gun did a pretty good job, it still failed to clear the via of solder.

So I used my tried and tested way of removing the capacitor; heat the solder on the via and gently pull the capacitor free.

This removed the capacitor but again the via still had a slight blockage of solder in it.

So I tried using my solder wick again; I prefer to use solder wick when doing this as it is less destructive than using a de-soldering tool. The land around the vias can be pretty thin in places and using a soldering iron and de-soldering tool can easily chew them up.

Using solder wick usually removes this risk as you simply place the wick over the via and place the soldering iron on the via.

This did the trick first time! So I went on to replace the 47uF capacitor

 

After that I decided that I would replace the original 1A rated 7805 with a new 2A rated version of the 7805 (L78S05CV).

Below is the location of the component and vias.

I found that the legs of the original 7805 hadn’t been trimmed so to make de-soldering easier for myself, I trimmed the legs.

Then I de-soldered the legs.

Next up I had to remove the M2.5 nut and bolt which fixed the 7805 to the heatsink.

It is not a good idea to use pliers to hold the nut when removing this as pliers can easily slip and cause damage to the traces of the PCB. So I prefer to use either a spanner, nut spinner or socket to hold on to the nut.

In this case I used a 5mm socket.

Remove the heatsink.

Then I found that the 7805 still wasn’t free of solder so I Solder Sucker instead of my de-soldering gun and this did the trick.

Now clean the old heatsink compound off of the heatsink using some IPA alcohol and a cotton bud.

Then bend the legs of the replacement L78S05 using pliers then check to see if the holes line up by placing it temporally on the PCB with the heatsink.

Now add fresh heatsink compound to the back of the L78S05.

Before soldering, fit and secure the voltage regulator and heatsink using the M2.5 nut and bolt using either a spanner, nut spinner or 5mm socket.

 

The reason I like to fit the nut and bolt before soldering is that sometimes the 7805 will move when tightening the nut and bolt and this in turn will cause some stresses and strains on the solder joints.

Then solder.

With all the components replaced it is time to refit the C16, starting with the RF shield.

Below is the locations of the metal clips to re bend into position.

Better look busy; the gaffer is here to check up on my work!

Bending the clips back into shape is simple; all you have to do is push them over with your finger.

The next part I found extremely awkward! This was due to me not taking enough time to analyse how I took the PCB out from the C16. When I tried to refit the PCB I couldn’t get it to locate properly.

I spent a fair bit of time faffing and fumbling about until I realised that the bezel has to be fitted in-between the PCB and RF shield!

I got there in the end!

The PCB and bezel fit perfectly now!

Now we need to secure the PCB with the 8 fixing screws; remember that there are 6 self tapping screws shown below.

And 2 machine type screws, locations shown below.

Refit all 8 screws.

Then refit the keyboard connector; this can only be fitted one way as there is a blanked out hole in the socket connector to the left of the connector.

Now refit the power LED connector; the red wire should be on the left hand side (pointing towards the middle of the PCB) as you look into the C16 from the front.

Now refit the lid of the C16 then screw in the 3 main fixing screws on the underside of the C16.

And here we have a fully re-capped with a new 7805 fitted C16.

 All we have to do now is test it!

Plug everything in and prepare to test; this is always a nervous moment!

And…

Success! The C16 booted up!

It is always a good idea to leave any re-capped computer on for a wee while whilst testing as sometimes (especially if you install a capacitor the wrong way round) it takes a wee while for the component to fail. So for this purpose I decided to load a game using my Tapuino.

Can you tell which game I am loading?

Looks a bit scrambled doesn’t it? I was a wee bit concerned at this point as this was the first game I have tried to load on the computer.

But…

After a bit of patience, and resisting the temptation to turn off the computer to check that everything was ok on the circuit board…

I was rewarded with this screen.

Can’t beat a bit of good old Monty Mole!

 

A you tube clip of this modernisation of the components can be found by clicking on the clip below.

Thank you for taking the time to read this entry; I have learned quite a bit about working on the C16 doing this relatively simple mod. This should make the other mods I have in mind for this computer a whole lot easier to do.

 

I think I am going to attempt to make a diagnostics rom next so that I can test the system for any faults with the RAM, TED chip etc. I am also going to fit a heatsink to the TED chip which will hopefully prolong the life of the machine.

 

If you have any questions or queries about this mod then please feel free to leave a comment or email me directly at

alleged_geek@aol.com

Thank you again