Restauration of a Commodore CBM 4016


I have always been a big fan of Vintage Computers.

After I bought a C64 this year for nostalgic reasons, I thought it would be a nice project to restore a CBM model.

I looked around and got a very good package with CBM 4016, 4022 and Datasette for a good price.

I really like this green/black monochrome monitor. This is amazing.

So this was the start of this project and I will describe what I had to do to get it running again.

Because of the low price the CBM was not working. But I like to get things back working.

Here you can see how the CBM 4016 looked like when I got it.



Part 1 (Troubleshooting):

When I plugged in the CBM the first time nothing happens. Really nothing.

So took my Voltmeter and had a look if there is current flowing in the power supply.

Okay, so it is flowing in, but after another measurement it was clear, that it is not flowing out of the power supply.

Then I checked the glas fuse and detected a broken fuse.

It was quite difficult to get this fuses in my area in this days, but luckily I found one who helped me out.

But when I inserted the new fuse and plugged it in, the fuse got instantly broken again. So there must be something shorten the power supply.



Part 2 (Repairing the Power Supply):

Because of the broken fuse, there must be something wrong inside.

So I dismounted the power supply from the CBM and did some measurements.

Really nothing is flowing at all.

So I looked for some help in local commdore forums and they gave me the tipp, that the noise filter might be broken.

After some research I found out how to remove the noise filter and shorten it. (This part is not really nessecary)

When it was done I inserted a new fuse and plugged in the power supply.

Yes, now the transformer is producing current.



Part 3 (Garbage Screen):

But I can only see a flashing garbage screen for a 1/10 second, followed by a beep sound.

I guess, that would have been too easy. So I needed to do further troubleshooting to detect if the screen itself or the mainboard is broken.



Part 4 (Mainboard Repair):

With some advice from a local Commodore Forum I was told to switch the IC of UA3 with UD6.

When doing this it is recommended to desolder the IC and place a socket.

Sadly there was no improvement because of that.


After that I step forward with doing this also with UD8 and UD10.

But also with this test there is no reaction.


Jumpering the CBM into Diagnostic Mode also makes no difference.

Last but not least using the soft reboot itself and in combination with the diagnostic mode does not affect a thing.


So my last option was to accept a very generous offer from a guy in the local commodore forum, who said I shall send the mainboard to him and he will have a look.

I am really confident that he is getting it repaired, he is really experienced with that type of computers.


So now, that my mainboard is on a little journey, I will focus on the other parts which are left.



Part 5 (Cleaning the frame):

As I said, I am paying attention to the parts which stayed at home.

So I decided to clean the dirt of the past 30 years.

First I disassembled the whole CBM to get every single part of it, to give it a nice clean.


With by Breff fat solvent I cleaned the whole white frame to make it really bright white.



Part 6 (Cleaning the keyboard):

As well the keyboard was quite dirty after 30 years and so I removed every single button on the keyboard to give it a full bath.

After some cleaning and drying they came out very nice.

When I finished assembling the keyboard it looks like brand new.

It will be a really beautiful CBM when it is finished.



Part 7 (Designing a Label):

Because from the old label was only a white border present, I decided to design a new label as replacement.

After some time it turned very well and good looking.



Part 8 (Repairing the CRT PCB)

A good friend found the damaged part on the PCB.

The resistors R752 and R753 were broken.

Luckely he had some original Spare Parte from 1982 which soldered into my board.

I heard that you can use 56 Ohm 1/4W of Coalcoat or Metallcoat instead, but in this case I prefered the original ones.

Here is a picture of the broken resitors.



Part 9: (Painting the CRT Frame)

There was a lot of rust on the frame of the CRT, so I took everything a part, sanded the frame and painted it with some creamy white.

Here you can see how the frame looks now.



Part 10: (CBM 4016 is alive)

Now everything is finished, it was time to start the CBM after month of work and troubleshooting.

I was so excited when I saw the first time the green letters on the CRT.

Of course I was prepared and bought month ago a cassette with some games for the CBM.

I put the cassette into the datasette and loaded "Space Invaders".

It looks so great on this Commodore device.