This is the video transcript. Read the original article with all the details →
Welcome back, guys, to the ValorosoIT channel.
Today we talk about the Commodore Plus/4 that I ordered on eBay. Do you remember? It arrived in disgusting packaging and, above all, it didn't work...
I was a little upset about that video. From the initial smile, we had arrived... at a slightly less final smile! But, well, it happened that way. Again in the same video I said something. I don't know if any of you remember this. I said I wouldn't try to repair it, because I didn't feel like it, I was fed up, I had so many things to do and instead I would have preferred to send it to a repairman.
As Schwarzenegger would say: I lied to you!
In this first repair video we are not going to make a purely permanent repair. Actually, I'm happy to see which components are damaged. To do this, I use a Commodore 16, mine, which I already have, with which we will exchange the various components.
It's a really simple repair (embarrassing!) because we go and take one integrated chip at a time, among those that we assume are broken, from the Commodore Plus/4 we put them on C16 and see if it turns on. Conversely, we will take those from the Commodore 16 and put them on the Plus4. Then, later, when we find out which components are damaged, I will go and look for replacement components or another Commodore 16, perhaps in pitiful condition, from which to recover them.
Every now and then, on my website www.valoroso.it, I publish some articles about some repairs of the Commodore 64, for example, or even the Commodore 16, in which I installed some transils.
What are transils for? They are used to protect the electronic components of the computer from overvoltages or voltage transients. Here, we won't assemble them now, however, in the next Plus4 video, when I find definitive components, I will also assemble transil. So, if you are interested, since many people ask me how to do it, which ones to choose, in the next video we will also see which transils to choose. Stay tuned to the channel, like if you like this video, subscribe and turn on the notification bell!
The first thing we do is check that my Commodore 16, the one I already own, still works.
The internal components, especially the TED (MOS8360) and the CPU (MOS8501 or MOS7501), are known to be delicate. So, before removing them and trying them on the Plus/4, I prefer to check that the computer turns on. Once we have verified that the Commodore 16 works, we can turn over both computers (so the Plus4 that I want to repair and the Commodore 16 that will act as a temporary component donor) and open them.
Under the Plus/4 there are some screws. On the bottom/front part there are two screws that need to be unscrewed. Instead, in the back, there are three more.
At this point we can rotate the upper body, taking care not to break the cable that connects the keyboard to the motherboard, which is very delicate.
I also open the metal cover that protects the TED (MOS 8360R2), which would then be the audio video processor of the Commodore Plus4 (3 plus 1).
We can, now, open the Commodore 16, which serves as a temporary donor of electronic components. On the bottom/front there are three screws to unscrew. Then, subsequently, you need to rotate the upper body backwards, taking care not to break the hooks located on the back of the computer itself.
So, you should never force it. You have to do everything very delicately, waiting for the parts to release automatically, by themselves, without using any force. At this point, we can detach the LED (the LED connector) and the keyboard connector, in order to free the two parts of the body: the lower one, which contains the motherboard, and the upper one, which contains the keyboard.
We also unhook the screen, which would then be a part of protection against the electromagnetic waves that computers can emit.
On the Plus/4 I clean the TED, which has become dirty with thermal paste. At this point, I can remove it by levering it with the screwdriver. We have already seen it in several videos, including the one on the repair of the Amiga 500: to remove such long ICs you don't have to pry from just one side. You need to use a little leverage on one side and a little on the other side, delicately, in order to remove all the feet vertically, without bending them. We do the same thing on the Commodore 16: I'm going to remove the TED (MOS 8360R2). I use a slightly smaller screwdriver, because the other one (a little bigger) couldn't fit between the integrated circuit and the socket. I, on the other hand, really want to leverage not on the printed circuit, but between the integrated circuit and the socket. At this point I can try the TED of the Commodore Plus/4 on the Commodore 16, taking care to orient it in the correct way. We connect the various connectors, then the video connector, the power connector, and then we try to turn it on to see if we see anything with the TED the Commodore Plus4.
Nothing, black screen! So we have TED confidence that Commodore Plus 4 (3 Plus 1) doesn't work, because we tested it on Commodore 16, which we saw was working. Let's replay his original TED and see that everything works...
To test the TED of the Commodore 16 on the Plus/4, and therefore see if this was the only damaged component, I have to change the power supply plug. If you remember, the power supply had an English plug and I found a very normal Italian plug, the one with three poles, even if in reality we only use two, since there is no earth on these computers. It's a bit of an old plug, if you notice!
Probably, it also comes from the 80s: the power supply will not undergo any updates. It remains in the 80s both in terms of the plug and the power supply itself.
Even though I already did it in the last video, let's test the output voltages of the power supply.
This is because I don't want the 5 Volt to be too high. Suppose we find the supply voltage at 6V or 7V, it could easily damage all the electronic components, including the new TED that I'm going to put on: the one from the Commodore 16 which worked and I want to avoid this!
Then, I check that all the voltages are correct: 5 Volts DC and 9 Volts AC. Obviously, there can be a certain tolerance, but they must be as close as possible to 5V as regards the direct voltage, and to 9V as regards the alternating voltage. The alternating voltage can easily be found at 10 Volts.
Once we have verified that the supply voltage is OK, we can verify that this voltage is propagated correctly within the computer. So, I measure around the TED a bit, without mounting the IC, where the socket is. I'm going to measure around to see that there aren't any strange tensions. I expect to find voltages up to 5 Volts. Perfect, that's how it is!
I insert the TED which is definitely working inside the Commodore Plus/4. When inserting slightly large integrated circuits, like this one here, it is best to press them simultaneously on both sides, so as not to bend the pins or break the chip. In short, you need to be decisive, but delicate!
We connect the power supply and the monitor cable, and try to turn it on.
No, it still doesn't work! So, besides TED there is another IC that is broken! So: the English seller who sold me this computer has little to say that he had tested it before sending it. Nobody believes it! An integrated circuit that breaks is one thing, but here, now, we must also talk about a second integrated circuit that has broken.
Normally, on these computers, the two chips that break most easily are the TED (MOS 8360R2) and the CPU (MOS 8501R1 or MOS 7501R1). And, coincidentally, they are also the most expensive chips in these computers.
The CPU from the Commodore Plus/4 is removed and I go to insert, in its place, the certainly functioning of the C16, paying attention to the correct orientation.
Here you go! The computer turned on! Here, be careful, the writing at the top is a little different than that of the Plus/4. If you notice, there is just one line missing compared to the normal Commodore Plus/4.
Now, unfortunately, you can't see it from the video, but I can tell you that a bit of a mess happened: basically some strange writing appeared on the computer... and it turned off!
So: not only the TED, not only the CPU are broken, but there is also another IC that is broken. So, I try to replace the first integrated one on the right, which is the PLA (the acronym is 251641-02). I also recovered this Commodore 16, which is definitely working.
Well! Now the computer turns on and the screen is the correct one of the Commodore Plus4.
We found three damaged chips! Three integrated circuits!
This is why I say that it is impossible that the seller was in good faith. I mean... three broken integrated circuits is a lot! Oh, and then we shouldn't forget the fuse, which I had already changed in the previous video, when I received the computer and wanted to try it. The fuse on the power supply, not the internal one of the computer, so it was the 5 Volt fuse. At this point I can close the cover that shields the TED. I don't want to put back, at this moment, the conductive paste, the thermal paste, because the TED is the one on my Commodore 16.
Then I close the keyboard, temporarily at the moment, without tightening the screws, so I can do some tests.
For example, let's try the keyboard: see if all the keys work.
Yes, everything works fine. I can also try starting the first of the programs pre-loaded on the machine. If you remember, the Commodore Plus/4 (3 Plus 1) has three other programs, in addition to Basic, that are preloaded on the machine. There is a text program inside, such as Notepad, or Windows Word, there is a kind of Excel, therefore with a spreadsheet with the various cells, and there is also a database.
Today we are doing some very quick tests, just to understand if the computer works, then, if so, we will delve deeper into the use of these programs and this computer in the future with other videos.
Well, we can say that computer works now. The broken integrated circuits are these three and I will have to take care of recovering them in the cheapest way possible. We've figured out which components are damaged and so I'll have to do some research to find them. If you are curious to know how much they will cost me, and above all how I will find them, stay tuned to the ValorosoIT channel, subscribe, activate the notification bell, so you will know immediately when I publish another video and you will not miss any updates.
See you soon!