Commodore PET, CBM 8032, test

Read in: IT 🇮🇹   EN 🇺🇸

Here, finally, is the test of the Commodore PET CBM 8032 that I had bought on eBay in the United States and which I had told you about in this video. I found a way to power it at 110V!

Subscribe my YouTube channel ValorosoIT. Retro technology, vintage audio, retro computers, experiments and tests. Retroprogramming, Basic. Commodore, IBM, Atari, Apple, Texas Instruments, Amstrad, MSX.

https://youtu.be/y2SiaPde8Vc

I hope you can get some ideas if you need to power some of your computers that run at 110V.

Power a computer at 110V

Computers arriving from the United States run at 110 Volts 60 Hertz. In particular, the Commodore PET CBM 8032, which I bought on eBay in the States, runs at 117V 60Hz, consuming just over 100W.

I found this transformer on Amazon: the Bronson++ VT-300. It transforms 220V to 110V, but does not change its frequency, which remains at 50Hz.

Transformer, converter, Bronson VT-300 USA UK voltage 110V 220V 240V

The Bronson++ VT-300 transformer has a power of 300 Watts (200W continuous), so it is suitable for the power drawn by the Commodore PET CBM 8032, which consumes just over 100W.

Posteriormente, ha l'ingresso di alimentazione. La tensione di ingresso di alimentazione può essere impostata tramite un selettore: 110V, 200V, 220V, 240V RMS.

Transformer, converter, Bronson VT-300 voltage USA UK 110V 220V 240V input voltage selector fuse rear panel

Davanti, il Bronson++ VT-300, ha due uscite: una a 240 V con spina inglese, una a 110 V con spina americana. Selezionando l'ingresso di alimentazione a 240V, l'uscita anteriore è a circa 105V.

Transformer, converter, Bronson VT-300 voltage USA UK 105Vac RMS tester

What happens if I power a 110V 60Hz to 50Hz transformer?

Prima di fare la prova del Commodore PET, CBM8032, per essere più consapevoli, studiamo un po' di teoria dei trasformatori!

A transformer is formed by a primary winding, the one we connect to 220 Volt or, in the case of my PET, to 110 Volt 60 Hertz, and one or more secondary windings.

Follow me on Instagram channel. Retro technology, Commodore, vintage audio, retro computers, experiments and tests. Retroprogramming, Basic. Commodore, IBM, Atari, Apple, Texas Instruments, Amstrad, MSX.

The windings are magnetically connected to each other via the air gap. The first equation we see is related to the nominal voltage of the primary winding (V1).

Calculation of transformer turns V 4.44 N f S B formula nominal voltage frequency
V1 = 4,44 * f * N1 * S * B

La tensione nominale dell'avvolgimento primario (V1) depends on the frequency f, by the number of turns N1 dell'avvolgimento primario e da altri fattori che vediamo tra poco.

In questo caso, la tensione nominale dell'avvolgimento primario (V1) is 117 Volt, we read it from the rear plate of the Commodore PET CBM 8032. The three factors (N1 * S * B) are constant, because we do not modify the transformer:

  • N1 è il numero di spire dell'avvolgimento primario;
  • S and B represent the shape and material of the metal.

4.44 is a number, that is, a constant by definition.

So, if V1 è uguale a 117 Volt efficaci a 60 hertz, vediamo che, abbassando a 50 Hertz la frequenza di alimentazione, si abbassa di conseguenza anche la tensione dell'avvolgimento primario, che passa quindi a 97,5 Volt in alternata, RMS.

Calculation transformer AC 50Hz 60Hz what happens lower frequency

Here, it is as if we no longer find a 117 Volt transformer, but, rather, a transformer of just under 100 Volts, which we have to power with just over 100 Volts. Somehow, we are a bit comfortable that the Bronson++ VT-300, which I bought on Amazon, gives me an output voltage of 105 Volts, instead of 110V.

Questo, perché si avvicina un po’ a quella che è la tensione nominale del "nuovo" trasformatore del Commodore PET che siamo andati a creare immaginariamente, portando da 60 Hertz a 50 Hertz e la tensione di alimentazione.

We can also make another reasoning: what would it take to bring this transformer back to 110 volts nominal? Let's reverse the formula.

Calculation of transformer turns V 4.44 N f S B inverse formula nominal voltage frequency
N1 = V1 / (4,44 * f * S * B)

We have already said that S and B they are constant. Suppose we want to keep it constant too V1, the nominal voltage of the primary of the transformer of the Commodore PET.

At this point, we realize that we should increase N1, il numero di spire dell'avvolgimento primario, perché, se riduciamo la frequenza (f) from 60 to 50 Hertz, which is found in the denominator (under the fraction), simultaneously increases the number of turns by 20 percent N1 dell'avvolgimento primario.

Obviously it's just theory, as we can't physically increase the turns of the Commodore's transformer.

Keeping the Commodore transformer supply voltage lower, then from 117 V to 105 V coming out of the Bronson++ VT-300, obviously it will also lower the voltage at the secondary of the transformer a little (V2), because the relationship between the coils N1 / n2 of the primary and secondary is constant (we are not going to modify the PET transformer).

Follow me on Instagram channel. Retro technology, Commodore, vintage audio, retro computers, experiments and tests. Retroprogramming, Basic. Commodore, IBM, Atari, Apple, Texas Instruments, Amstrad, MSX.

Calculation of secondary voltage transformer turns ratio
V2 = (N2/N1) * V1

Hence, lowering V1 (the voltage of the transformer primary), it also lowers V2 (the voltage of the secondaries).

We have two possibilities:

  • if we keep the primary voltage of the PET transformer at 117V, when this is not designed to do so, because the mains frequency is at 50Hz against 60Hz, the transformer could heat up;
  • by lowering the voltage at the primary winding too much, we will also have a lowering of the voltages at the secondary windings, which may not be sufficient for the PET voltage regulators.

Con il Bronson++ VT-300 comprato su Amazon, poniamo la tensione di ingresso più o meno metà tra queste due situazioni. Cerchiamo di minimizzare l'effetto termico sul trasformatore del Commodore, tenendo più bassa la tensione V1, but we try not to lower it too much V2.

Schemi elettrici dell'alimentatore del Commodore PET, CBM 8032

How does this affect the Commodore PET?

Andiamo ad analizzare lo schema elettrico dell'alimentatore del Commodore PET.

Commodore PET CBM 8032 CBM8032 8032029 regulator power supply wiring diagram

The secondaries of the PET transformer go to rectifier bridges and the AC voltage is rectified and smoothed by the capacitors. At this point, after it has been straightened and smoothed, the voltage no longer has the frequency: neither 50 Hertz nor 60 Hertz. It has frequency 0, since it is a direct voltage!

Subsequently, the rectified and smoothed voltage goes to the various voltage stabilizers: LM340-5, 7812, 7905, which regulate the various direct voltages (5V, 12V and -5V) necessary for the functioning of the motherboard of the CBM 8032.

Dallo schema, non vedo una criticità abbassando la frequenza da 60 a 50 Hertz perché da nessuna parte passa questa frequenza. Al limite, tenendo un pochino più bassa la tensione all'ingresso dei regolatori, è possibile che la tensione sia troppo bassa rispetto a quella necessaria. However, later, when we feed the PET, we will check that the regulated voltages are actually the correct ones.

Follow me on Instagram channel. Retro technology, Commodore, vintage audio, retro computers, experiments and tests. Retroprogramming, Basic. Commodore, IBM, Atari, Apple, Texas Instruments, Amstrad, MSX.

C'è un'altra presa al secondario del trasformatore, che è quella che va al PCB del CRT.

Wiring diagram CRT monitor Commodore PET CBM 8032 CBM8032 PCB 321448

La tensione di alimentazione alternata entra nel punto indicato in basso a sinistra dello schema elettrico del CBM 8032. Vedete che c'è proprio scritto: 50/60 Hertz il che vuol dire la scheda è predisposta per entrambe le frequenze. In effetti è vero, perché la tensione viene raddrizzata, livellata e regolata, come abbiamo visto in precedenza.

That said, I feel pretty confident that my Commodore PET will work by the time I feed it with a voltage of 50 Hertz, rather than 60 Hertz.

Collegare il Commodore PET, CBM 8032, all'alimentazione

To test the Commodore PET, CBM8032, we can proceed to make the electrical connections. The power plug of the computer must be connected to the front 110V socket of the Bronson++ VT-300.

Commodore PET power supply, CBM 8032, retro computer, vintage collection, 117V 60Hz 50Hz 220V

L'ingresso di alimentazione posteriore del Bronson++ VT-300 si collega alla presa elettrica di rete 220V 50Hz.

For the sake of consideration, we also open the computer, to measure, with the tester, the various DC voltages after we have turned it on. We have seen in the previous article how to open the Commodore PET, CBM8032.

We light up?

L'interruttore posteriore del nostro Commodore PET CBM8032 e già posizionato su ON. Bisogna anche accendere il Bronson++ VT-300.

Subscribe my YouTube channel ValorosoIT. Retro technology, vintage audio, retro computers, experiments and tests. Retroprogramming, Basic. Commodore, IBM, Atari, Apple, Texas Instruments, Amstrad, MSX.

E' ore di alimentare il Commodore PET, CBM 8032

Il Commodore PET, CBM 8032 emette il classico suono all'avvio! E partito!

La tensione di alimentazione è corretta. Il tester è collegato sui 5 Volt, che uno dei voltaggi più critici all'interno di un computer: deve essere regolato correttamente perché, se è troppo alto, fa bruciare tutti i circuiti integrati.

Ignition Test Test Commodore PET, CBM 8032, open, 5V 12V DC voltage test

The monitor shows some writing! Fantastic!

Ignition Test Test Commodore PET, CBM 8032, retro computer, vintage collection, monitor on monochrome CRT *** commodore basic 4.0 *** 31743 bytes free ready

Meglio spegnere subito il computer: bisogna dare tempo ai condensatori di rigenerarsi. Dopo tanto tempo che un computer (ma anche un impianto stereo, una radio, ecc...) rimane spento, i condensatori hanno necessità di un po' di tensione, ma anche di un po' di riposo! Lo spiego in this article.

After a few minutes of rest, we can turn the computer back on and try all the other power supply voltages: 5V, -5V and 12V again.

We can also note that the transformer does not heat: it is cold.

The Commodore PET test, CBM 8032

Here, the first thing I notice is that the writing Commodore Basic 4.0 wobbles a little. I will have to inquire if it is normal or if it is a defect to be investigated. It is as if it moves left and right by a millimeter.

Also, the vendor had already informed me that the keyboard was not working properly.

Follow me on Instagram channel. Retro technology, Commodore, vintage audio, retro computers, experiments and tests. Retroprogramming, Basic. Commodore, IBM, Atari, Apple, Texas Instruments, Amstrad, MSX.

Not even a button goes!

I would like to make sure the keyboard problem is not related to the motherboard. Let's see the wiring diagram.

Cassette keyboard wiring diagram, user port, Commodore PET CBM 8032 CBM8032 MOS 8520 8032029

The keyboard is managed in a similar way to that of the Commodore 64. It is scanned in rows and columns, through the integrated MOS 6520 circuit, otherwise known as PIA.

Let's do a test with a piece of electric wire. On the keyboard connector, we try to simulate the pressure of a few keys, joining, through the electric wire, a few lines with a few columns.

Ignition Test Test Commodore PET, CBM 8032, open, test keyboard connector jumper

A monitor... c'è scritto qualcosa! Aveva ragione il venditore, è la tastiera a non funzionare.

Ignition Test Test Commodore PET, CBM 8032, open, CRT test keyboard connector jumper, *** commodore basic 4.0 *** 31743 bytes free ready

Continua ...

Prossimamente, dovremo smontare la tastiera è vedere che cosa c’è che non fa contatto, su nessun tasto. Mi stupisce che nessun tasto della tastiera funzioni. Quindi, o si sono seccati tutti i gommini che premono sul circuito stampato, oppure c'è dell'ossido. Ma questo è soltanto il futuro ce lo dirà.

To be notified when I publish more videos related to retro computers and vintage electronics, I invite you to subscribe to the YouTube channel and activate the notification bell!

Subscribe my YouTube channel ValorosoIT. Retro technology, vintage audio, retro computers, experiments and tests. Retroprogramming, Basic. Commodore, IBM, Atari, Apple, Texas Instruments, Amstrad, MSX.

Posted in Retro Computer, Retro Technology and Vintage Electronics, All articles.

Leave a Reply

Your email address will not be published. Required fields are marked *