Today we talk about the repair of the Commodore Plus/4, which I had ordered on eBay. Do you remember? I had arrived with an inadequate packaging and, above all, not working ...
Repair of the Commodore Plus/4, fault diagnosis
In this first article of the repair of the Commodore Plus/4, we are not going to make a definitive intervention. Actually, I'm content to see what the damaged components are.
To do this, I support a Commodore 16, which I already have in my collection, with which we exchange the various components.
The concept behind this quick repair is to take one supplement at a time, among those that we assume are broken. From the Commodore Plus/4 we put them on the C16 and see if it turns on. Conversely, we will take those of the Commodore 16 and put them on the Plus4.
The first operation to be carried out is to verify that the Commodore 16, present in my collection, functions correctly. Luckily ... it works!
Why this repair approach?
E' risaputo che alcuni componenti interni al Commodore 16, 116, Plus/4 (insomma, tutta la serie Commodore 264), sono molto delicati:
- TED (MOS 8360 audio/video processor);
- the CPU (MOS 8501 or MOS 7501 microprocessor);
- PLA (programmable logic array MOS 251641-02).
Questi componenti possono danneggiarsi per età ed ossidazione, oltre che per surriscaldamento. Per questo, può capitare di riporre i computer funzionanti, lasciarli spenti per alcuni anni, e trovarli danneggiati all'accensione.
Open the Commodore Plus/4 and Commodore 16
Once we have established that the Commodore 16 works, we can turn both computers (both the Plus4 and the C16 that will act as a temporary donor of components) and open them.
To open the Commodore Plus/4 there are 5 screws to unscrew: two at the bottom/front and three at the bottom/back.
At this point you have to rotate the upper body, to the left, taking care that you do not break the cable that connects the keyboard to the motherboard, which is very delicate.
We also open the metal cover that protects the TED (MOS 8360R2), which would then be the video audio processor of the Commodore Plus4 (3 plus 1).
We continue the repair of the Commodore Plus/4 ... opening the commodore 16, which acts as a temporary donor of electronic components! In the lower/front part there are three screws to unscrew.
Poi, successivamente, bisogna ruotare verso l'indietro la scocca superiore, prestando attenzione a non spezzare i gancetti che si trovano posteriormente al computer stesso. Nel video, in alto a questa pagina, si vedono bene tutti i passaggi. You must never force. You have to do everything in a very delicate way, waiting for the parts to come off, without making any force.
We free the two parts of the body of the Commodore 16, detaching the LED connector and the keyboard connector. We also release the screen, which would then be a part of protection against electromagnetic waves that computer can emit.
First test: supply voltages!
Never, never, never turn on a vintage computer without having tried the supply voltages. I had talked about it in this article.
Prima di tutto, ho dovuto mettere una spina italiana sull'alimentatore del Commodore Plus/4, che arrivava dall'Inghilterra.
Successivamente, dobbiamo provare le tensioni di alimentazione in uscita all'alimentatore: 5V in continua e 9V in alternata. Ovviamente, ci può essere una certa tolleranza, però devono essere più vicini possibile a 5V per quanto riguarda la tensione continua, e a 9V per quanto riguarda la tensione alternata. La tensione alternata la potete trovare tranquillamente anche 10 Volt.
Let's test the TED, MOS 8360R2
Per togliere chip così grossi, bisogna fare leva, con un cacciavite, tra lo zoccolo e il circuito integrato. Bisogna fare un pochino di leva da una parte del chip ed un pochino dall'altro lato, delicatamente, in modo da togliere tutti i piedini in verticale, senza piegarli. Per tutti i dettagli, guardate il video.
We have already seen it in several videos, including that of the repair of theAmiga 500: When removing chips from the sockets, you must leverage NOT on the printed circuit board, but between the integrated circuit board and the socket.
Let's take the TED (MOS 8360R2) of the Commodore Plus/4 and try it on the Commodore 16, obviously after removing the TED of the Commodore 16 from its socket. Quando mettono i circuiti integrati, bisogna tener conto dell'orientamento corretto.
The ignition test of the Commodore 16, with the TED of the Commodore Plus/4, gave a negative result. The Commodore 16 has not started and remains with black screen.
This proves that the TED of the Commodore Plus4 is damaged.
Before putting the working TED, that of the Commodore 16, inside the Commodore Plus/4, we check if the 5V supply voltage is propagated correctly on the computer motherboard.
Inseriamo il TED, sicuramente funzionante, all'interno del Commodore Plus/4, prestando attenzione all'orientamento corretto.
Then, let's try to turn on the Commodore Plus/4, hoping it will start.
No, non funziona ancora! Quindi, oltre al TED c'è un altro circuito integrato che è rotto!
Let's test the CPU, MOS 7501R1
La riparazione del Commodore Plus/4 continua... con l'elenco dei chip delicati visti prima. E' il momento di provare la CPU.
Rimuovo, quindi, la CPU dal Commodore Plus/4 e vado a inserire, al suo posto, quella sicuramente funzionante del C16, prestando attenzione all'orientamento corretto.
Actually, the CPU I removed from the C16 is a MOS 8501R1, which is compatible with the MOS 7501R1.
With the new CPU ... the computer has turned on!
Per chi non volesse utilizzare la CPU originale del Commodore 16, dato che è costosa e delicata, c'è possibilità di utilizzare una CPU MOS 6510 (quella del Commodore 64), con opportuno adattatore che si trova anche su PCBWay.
Paying attention, the writing at the top, of the home screen, is a little different from the correct one of the Plus/4.
Se notate, manca proprio una riga rispetto a quella del Commodore Plus/4 funzionante. Lo vediamo, confrontando la schermata iniziale con questo screenshot, preso dall'emulatore VICE for Windows PC.
Furthermore, unfortunately it is not seen from the video, it happened a little a mess: the computer showed random breakwriters and ... went out after a few seconds!
So: not only the TED, not only the CPU are faulty, but there must also be another faulty integrated circuit.
Replace PLA MOS 251641-02
Let's go in order ... with the third most delicate chip of the Commodore Plus/4. La Pla (Programmable Logic Array Mos 251641-02).
We can also recover this chip from the Commodore 16, certainly working.
Con quest'ultima sostituzione, il computer si accende e la schermata è quella giusta del Commodore Plus4!
We found three damaged chips!
Commodore Plus/4 test
At this point, we can close the lid that shields the TED. I don't want to put the thermal paste back right now, because the TED is that of the Commodore 16.
We can close the keyboard, at the moment temporarily, without screwing the screws, just to do some tests. For example, let's try the keyboard: let's see if all the keys work.
We can also try to start 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 the Basic, which are preloaded on the machine.
This is software from International Tri Micro Inc., david W Johnson.
The software includes a text program, similar to Windows Notepad or Easy Script del Commodore 64. C'è anche un foglio di calcolo, simile ad Excel, e c'è anche un database.
Well, the first tests gave a positive result!
We have figured out what the damaged components are and I will have to do some research to buy them at a good price.
If you are curious to know how much they will cost me, and above all how I will find them, stay tuned on the ValorosoIT channel, subscribe, activate the notification bell, so you will know immediately when I publish another video and you will not miss any update.
Good morning! Thank you for the very interesting and very useful videos in terms of any repairs.
In this regard, I also received a non-working Commodore Plus/4 with the same vicissitudes and its partial refund!
Ora, avendo constatato che uno dei componenti guasti è il famigerato MOS7501, mi chiedevo se il sostituirlo con il MOS8501 possa essere una soluzione migliore ovvero, sostituendo il 7501 con l'8501, si potrebbe andare incontro ad eventuali "incompatibilità" con altri componenti?
Grazie per l'eventuale risposta.
Good morning! Unfortunately, it happens to receive non-compliant objects. You can replace the MOS7501 with the MOS8501, try to see what you can find at a better price. In addition, there are kits to use the MOS6510 as well, but in this case there will be incompatibilities.