C128 [PAL]
Ser. No. 269919
Artwork 310381
(REV 7)

Starting point

From the outside this flat C128 does not have the best looking appearance. The top cover, and even some of the keys, is full of scribbles. There is also some scratches on the cover. There is a Norwegian keyboard layout, but it seems like the printing of the Norwegian characters "Æ", "Ø", "Å" (and also the "@") is more worn compared to all the other keys. I would guess this is due to different manufacturing methods.

On the bottom cover the situation is quite the same as the front cover, except that there are no scribbles. A lot of marks and scratches. Also there is a Norwegian marking saying "GARANTINUMMER" which translates to "WARRANTY NUMBER" in English.

I do not know in advance if this machine works or not...

Refurbishment plan

The refurbishment plan for this flat C128 (several of them in parallell):

- Refurbish the casing (cleaning, repairing and retrobrighting)
- Refurbish the keyboard (cleaning, reviving the plungers and maybe retrobrighting)
- Refurbish main board (cleaning, checking, repairing, replacing capacitors and voltage regulators, adding heat sinks etc.)
- Recap RF-modulator
- Verify operation by testing

The plan can be updated during the refurbishment process. Sometimes I discover areas that needs special attention.

Opens it up...

Opening a C128 is not difficult, but it is wise to be somewhat careful to not break any of the brittle plastic. First action is to remove the six screws from the bottom cover.

Now comes the careful part. On each side of the top cover there is a small plastic clip which can easily break if not careful. To find the position of this plastic clip follow the thin embossed line just above the numeric keypad. See picture below for where this embossed line is located.

With a thin flat screwdriver the clip is gently pushed inwards while the top- and bottom cover are wiggled loose. This is not super easy, so it is wise to not rush this. Below is a picture of the small plastic clip when loose.

The top cover is slid slightly to the side so that the ground screw is exposed. This screw is removed so that the top cover can be lifted further.

Next, the keyboard connector is removed. This is quite "stuck" and require the use of a thin small screwdriver to carefully pry it open. I have seen this on other C128 before so I think this is quite normal.

Finally, the LED connector is removed and the top cover is free.

The RF-shield is now revealed. There are no signs of corrosion on the RF-shield, some sign of corrosion on the cartridge port and lots of corrosion on the RF-modulator. Nevertheless, this should not affect the machine in any significant way. Also, there is plenty of dust inside here, but that is expected after all these years. To remove the RF-shield all the six screws are removed, all the eight metal tabs are bent in a straight position and the plastic pole in the middle is locked to the shield with some tabs (see arrow).

With the RF shield out of the way the mainboard is revealed in all its glory! There is a LOT of dust and grease inside and dried out cooling paste - but it otherwise looks to be in good condition.

Eventually the small metal tabs in the joystick port / keyboard connector area are straightened, and the mainboard is lifted out of the bottom cover.

Exterior casing

Both the top- and bottom cover is a sad spectacle. They are full of scribbles made from what looks like tools such as a ball point pens and crayons (?). There are also some scratches, but I think they are not too bad. Before cleaning the LED, rubber feets and "Garantinummer" (eng: warranty number) sticker are removed. Removing the LED is not difficult, but requires a bit of careful fiddling loosening the small black plastic clip. The "Garantinummer" is gently removed with some hot air from a hair dryer while prying it off with a thing spudger. The reason for removing the rubber feets is that these can be damaged (they become "sticky") if I decide that the covers needs chemical retrobrighting. In the picture gallery below all of these parts are shown (click to enlarge).

Below is a picture of the top- and bottom cover before cleaning and retrobrighting. Hopefully most of the scribbles will be possible to remove.

Both top- and bottom cover are soaked in mild soap water for about 24 hours. This removes most of the fat and grease. The remaining stains are removed with isopropanol on a Q-tip. The covers are not very yellowed, but I decide to retrobright these anyway. 12 % hydroperoxide cream is applied regularly to the covers (wrapped in cling film) and exposed to UV-light for about 12 hours. See picture below.

The result av this thorough cleaning and retrobrighting is very good I think. There are some few scratches, but they are not easy to detect I think. I am very pleased with the result.

Keyboard

The keyboard needs to be disassembled from the top cover. This is done by first removing the six screws from the backside of the keyboard. See arrows in the picture below.

Note that there are four plastic spacers beneath the top screws. It is a good idea to lift these off the metal top cover before cleaning to avoid loosing them later. In the picture two of these plastic spacers are shown.

Next, the wires connected to the SHIFT-LOCK, CAPSLOCK ASCII/CC and 40/80 DISPLAY keys are desoldered. The wires are twisted around the small metal pins on these keys. While using the soldering iron on the wires the wires are lifted from the pins with a pair of tweezers.

The keys are very dirty and some of them have scribbles. To remove the keys for cleaning a key puller is used. This is the most gentle way to remove the keys - reducing the risk of damaging plungers and/or keycaps. Note that there are two small additional springs beneath the spacebar which is wise to keep separately. Also, one some of the keys (such as the enter key) there is a U-shaped metal bracket. NOTE: to remove the special keys such as the SHIFT-LOCK push firmly from the backside of the keyboard towards the front.

All the keys are placed in a plastic container filled with mild soap water for about 48 hours. Next, the 27 small screws at the backside of the keyboard are removed. This will reveal the PCB which are cleaned with some battery water (distilled water). As can be seen in the picture below the keyboard PCB is a MITSUMI C-128P 56 3092.

With the keyboard PCB out of the way the plungers are exposed. Note that the top row have plungers which are of a different colour. I am not really sure why that is the case as the form factor appears identical otherwise.

It is common that old Commodore 64/128 keyboards requires the keys to be pushed very hard, or hammered several times, in order to generate a key response. This is often due to either dirt on the carbon pads on the PCB - or that there are fat and grease on the conductive rubber on the plungers. To revive the conductive rubber the plungers are carefully rubbed over a clean sheet of paper.

Each of the specialized keys are inspected and the exterior is cleaned. At this stage they are not opened for cleaning inside - I think it is possible to open these the same way as the SHIFT-LOCK key on the Commodore 64, but they appear to work as they should.

The metal plunger holder is cleaned properly with mild soap water. This was full of old dirt, dust and grease and requires thorough cleaning. Eventually all the plungers are put back in the holder and the PCB re-attached. The end result looks very good - almost like new (?)

The spacebar is retrobrighted for about 1,5 weeks. The rest of the keys are not very yellowed. Below is a picture of the keyboard after cleaning (and retrobrighting the spacebar).

Mainboard

This is an Artwork 310381 (Rev 7) mainboard. Below are a pictures of the mainboard before refurbish.

Visual inspection

Before testing the mainboard a visual inspection is carried out with the following findings:

  • The top half of the mainboard (near the row of ports) is very dirty. Not so easy to see in the picture, but there is a thick layer of fat/grease/dust.

  • The top lid of the RF-modulator is rusted. There is also some rust on the rest of the metal can, but it is not very severe.

  • Some corrosion on the metal lid on the cartridge port, but should not affect the functionality in any way

  • All DRAM chips are MT4264-20. There are notorious for failing. Should be considered replaced.

  • There is a lot of something that looks like medical tape. I am struggling to see the point of these, but I assume that they are used as some kind of insulation.

  • Even if the mainboard is dirty I can not see any signs of corrosion on the board (except for the RF-modulator and cartridge port lid).

  • There are some flux residue on the backside of the mainboard from the soldering at manufacturing time

  • All bodge wires are from manufacturing. I can not see any signs of rework.


In the table below the main chips are listed (before refurbishment - some may be changed during repair if required).

As can be seen from the table above most of the ICs are manufactured somewhere around Q2 1985. So it is a fair guess that this Commodore 128 was produced sometime late autumn in ´85. Perhaps a Christmas gift for a Norwegian child in 1985?

Initial testing

Powering on the C128 result in a: semi-garbled startup screen (?)

The keyboard, and the machine in general, seems to be semi-operational. You can type on the keyboard and access the Commodore 64 mode, but there is a lot of garbage on the screen.

Not very surprising since these machines are getting quite old, but it now means that repair is required. My guess is that this is related to the RAM chips, and that some of these are bad.

Checking the voltages

For the Commodore 128 to work flawlessly the voltage levels needs to be with acceptable levels. The fault symptoms do not suggest that there is an issue with the voltages, but it is good practice to measure these - and to rule out that there is a problem with voltages. In the table below all the measures voltages are listed (this list will also be updated after refurbishment). All the required voltages are present and within tolerances, so there are nothing obvious wrong in that area.

Cleaning the PCB

As previously mentioned the mainboard is very dirty. Even though it has nothing to with the fault I clean the board properly by using plenty of mild soap water and a soft paint brush. Note that all socketed chips are removed before cleaning to avoid water being stuck in the IC socket, and that the old labels are damaged. Some of the grease are removed with isopropanol. Below are some pictures after the cleaning. It looks way better, and makes the repair job more comfortable.

Hot ICs and Dead test cartridge

The Dead Test Cartridge is installed in the machine, and while the machine is powered on I also check if any of the ICs are abnormal warm. The ICs are quite warm, but nothing which is not normal as far as I can tell. Even if the Dead Test Cartridge is primarily focused for the Commodore 64 it is designed to work in the Commodore 128 as well (it will automatically force the machine into C64 mode).

With the Dead Test Cartridge installed the screen flashes six times. According to the diagnostic manual this points to a fault in RAM chip U40 or U48. See table below.

The Dead Test Cartridge do strengthen my hypothesis that there are bad RAM chip(s). Now, there are 16 of these and they should all be replaced actually. These MT RAM chips are prone to fail eventually. But in an attempt to check my hypothesis the U48 IC is desoldered and a socket installed.

Did that solve the problem? No... actually, with a new know working DRAM chip in place the computer goes light grey and then BLACK (!) after about 10 seconds. So now something else broke... I think that the MT chips are literally just failing in front of me here.

With the the "piggyback" method (placing working chips on top of the existing chips) I make some progress. Below are some pictures from the array of MT RAM with two ICs piggybacked (U40/U51) and one IC socketed (U48).

Now things start to happen! The Commodore 128 bootup screen looks normal, but when entering the Commodore 64 mode the "?OUT OF MEMORY IN 0" error message is displayed.

According to the Pictorial C64 Fault Guide the "?OUT OF MEMORY ERROR IN 0" points to a fault in the RAM ICs. No surprise there. Only thing I notice is that there is an additional blank character between the word "MEMORY" and "ERROR". Nevertheless, these MT RAM chips must be removed. All of them!

Following the best 8-bit repair mastermind, Ray Carlsen, all of the 16 DRAM MT chips can be replaced by a device called SaRuMan128. So such a device is ordered from retroleum.co.uk.

Installing the SaRuMan128

SaRuMan-128 replaces the original 16 DRAM used for the C128´s main RAM (made by Eslapion) - not only is it a modern replacement is uses much less power also.

As the SaRuMan-128 replaces all DRAM they must be removed first. This is done by simply cutting all the legs close to the IC body. Not strictly required but the cut pins are desoldered from the mainboard. Looks better and would make it easier if they are to be socketed at some point in time. The U51, U52 and U53 are desoldered and three sockets installed. These sockets will hold the SaRuMan-128.

The following wires are soldered between the SaRuMan-128 and the mainboard:

  • SaRuMan-128 D0 <> U46 PIN #2

  • SaRuMan-128 D1 <> U47 PIN #2

  • SaRuMan-128 D2 <> U48 PIN #2

  • SaRuMan-128 D3 <> U49 PIN #2

  • SaRuMan-128 D4 <> U50 PIN #2

  • SaRuMan-128 /CAS <> U44 PIN #15


And then the SaRuMan-128 is carefully placed in three sockets in U51, U52 and U53.

With the new SaRuMan-128 RAM replacement in place it is time to test the machine again. Does it work? Result: SUCCESS! Now both the C128 and the C64 boot screen appear normal. Further testing needs to be done, but this looks very promising!

Testing the 80 column mode without proper monitor

The C128 is capable of displaying both a 40- and 80 column screen. It is probably the 40 column mode which is most commonly known since this is the video mode generated by the MOS 8566 VICII-E chip used in both the Commodore 64 and 128 mode. The VICII-E can also generate advanced graphical objects such as sprites in contrast to the MOS 8563 VDC chip which is used for the 80 column mode. The VDC can show limited graphics (compared to the VICII-E), but is superior in displaying text used in business applications.

To test the 80 column mode without a proper monitor, but with a normal TV instead, a composite video cable can be made. But this video cable will only carry the monochrome signal from the RGBI connector. To make such a simple video cable the PIN #7 (Monochrome) and PIN #1 (Ground) from the RGBI port is connected to the center (PIN #7 - Monochrome) and shield (PIN #1 - Ground) on the video cable.

Below is the RGBI pinout shown. This is taken from the website My old computer - see reference documentation.

The homemade monochrome video cable is shown below. It doesn´t look good, but it does the job!

The 40/80 DISPLAY key is pressed and the 80-column mode is displayed. It looks to be fine!

Replacing the electrolytic capacitors on the mainboard

The electrolytic capacitors are almost 40 years old. And these capacitors will dry out eventually. Even if they good be in ok condition it is good practice to replace these fourteen with modern quality electrolytic capacitors. A list of which electrolytic capacitors that are replaced can be found in the library section. Below is a picture of the mainboard after the new capacitors are installed.

Replacing the 12 volt regulator

There is a 7812 voltage regulator (12 V) on the mainboard (marked U59). As part of best practice for refurbishment this is replaced with a modern replacement. The old 7812 is desoldered without any damage on traces and pads, and the new 7812 regulator is soldered in place. See pictures below.

Replacing the electrolytic capacitors - RF modulator

This Commodore 128 is equipped with an original Commodore RF-modulator P/N 251916-02. According to the capacitor list this RF-modulator contains two electrolytic capacitors: 1 x 10 uF [16V] and 1 x 220 uF [10 V].

Removing the RF-modulator is not trivial. Although it is not very difficult, you need to make sure you do not damage either the RF-modulator or the mainboard in the desoldering process. To get a detailed description on how I do this please check the HOWTO article "Desolder the RF-modulator". The desoldering of the RF-modulator was done without any damage. But I did notice something strange. When desoldering the RF-modulator I see that pin #1 and pin #2 are a bit shorter than the other six pins. At first I though this was me who had lifted the pins, but if that was the case they should have been longer. When pins are damaged they are dragged from the RF-modulator in the process, so if that was the case they should be longer and not shorter. Also, when I open the RF-modulator metal can I can see absolutely no damage inside. All joints are perfectly undamaged. To this leaves me to the conclusion that these pins were actually smaller when assembled back in the autumn 1985.

In the picture below the RF-modulator can is shown and the two pins to the left (pin #1 and #2) are indicated.

Pin #1 and #2 are connected to +5 VDC and Sync/Lum respectively. So if there is any problem when the RF-modulator is soldered back in after re-cap it will be obvious: either the RF-modulator has no power or no Sync/Lum signal. But I do not think this will be a problem. The pins are long enough to pass trough the PCB holes. In the schematics below the inputs to the RF-modulator is shown (taken from the Service manual for C128/C128D).

On the mainboard there is no damage at all - or anything suspicious looking. See picture below from the desoldered area when the RF-modulator is desoldered.

The two electrolytic capacitors are desoldered and new capacitors are soldered back in. No traces or damage. See picture below - the picture to the left (top) is with the old capacitors and the picture to the right (bottom) is with the new capacitors.

Cleaning the user- and datasette port

A very easy operation, but which can give great results, is to clean the user- and datasette port. After 40 years these ports will be covered with dust and grease, and often oxidized. To clean these ports a standard rubber eraser is used to "scrub" the metal connectors. This will remove most of the grease and fat without damaging the metal traces. Finally the ports are cleaned with isopropanol on a Q-tip. See pictures below of the cleaned ports.

Adding heatsinks to custom ICs

The large RF-shield is preventing the transmit and receipt of electromagnetic interference. But in addition it acts as a large heatsink. Unfortunately, this RF-shield will also entrap heat. So, to provide the most efficient heat dissipation heatsinks are placed on the major custom ICs and the RF-shield is removed. Heatsinks are placed on: SID, both CPUs, MMU, PLA, VIC and VDC.

Testing

Proof is in the pudding - does it work?

Testing a C128 is like testing three machines: C64, C128 and CP/M (Z80). Most of the testing is based on the C64 mode since this is where most of the test tools are available, but also since these chips are used for the C128 as well.

Testing is done through three main stages:

  1. Testing the basic functionality and chips (C64/C128 mode)

  2. Testing by using the machine playing demos, games etc. accessed by both floppy and datasette to verify correct operation (C64/C128)

  3. Testing C128 and Z80 specific features: 80 column mode (VDC chip) and CP/M mode

Basic functionality and chips

First test is done using the Dead Test Cartridge. This test doesn´t test all the functionality of the Commodore 64/Commodore 128, but it does test the basic functionality of the major chips such as the CIA #1/2, CPU, VIC-II, PLA, RAM and SID. As the picture shows below the test is passed.

Next test is to power the Commodore 64/Commodore 128 to the boot up screen and also check the keyboard to make sure all keys works as they should. The test is passed; all keys works and 38911/122365 BASIC Bytes Free. Note that the 40/80 column display is disabled in the key test. The 40/80 column mode will be tested separately.

The basic functions of the VIC-IIe, SID and RAM is tested with 64 Doctor and Commodore 64 SID tester. Note that this is to be considered as basic functionality - more advanced (?) functionality such as sprite handling / collision detection / advanced audio will be tested later. But the basic tests pass without any detected faults (click to enlarge).

Last basic check before moving to more extensive testing is checking the cartridge. This is done by using the Super Snaphot V. Result is that the test is passed.

Extended testing

Knowing that the basic functionality of the machine works I continue the testing by using the Commodore 128 for normal operations; playing some games, watching demos, loading from datasette and floppy and using a cartridge. I can not find any issues with this machine. I also pay special attention to the video to make sure that there are no glitches in the graphics - I can´t see any abnormalities. Below is a gallery with pictures from the testing.

80-column mode (VDC) and CPM/M

The Commodore 128 is capable of producing a 80-colum mode (in colours) using the MOS 8563R9 VDC chip. I do not have a proper monitor to test this, but the custom made monochrome cable described in earlier chapter is used. To activate the 80-column mode the "40/80 DISPLAY" key is pressed. This will disable the normal screen (making it secondary) and switch to 80-column mode on the RGBI-port. As the picture below shows the RGBI output (in monochrome) is present and working.

We do know indirectly that the Zilog Z80 CPU works. The reason for this is that the Zilog Z80 is used to boot up the Commodore 128 in "128-mode". Nevertheless, it is good practice to test the CP/M capability of the Commodore 128. To so this a 1571 disk drive is emulated using the UltimateII+ cartridge and CP/M 3.0 software is loaded. Both disk drive loading and running og CP/M works as it should.

Final result

"A picture worth a thousand words"

Below is a collection of the final result from the refurbishment of this Commodore 128. Hope you like it! Click to enlarge!

Banner picture credits: Evan-Amos