View Full Version : Commodore CBM-8032 European model 220V issue

February 20th, 2017, 02:23 AM
Hi, I recently bought a Commodore CBM-8032 which was sold as defective. After the usual cleaning and checks, I confirmed that at powerup it was not working: 5V current was missing.

The issue was in the transformer, I was getting to much voltage out of it. Eventually I started the computer using a dim bulb tester in order to get a few volts drop and it worked perfectly, except for the screen which was slightly distorted, too much drop there ;)

Now, I live in Europe (precisely in Italy), so we're talking 220V machines. Since a few years Europe switched to 230V (233V according to my voltmeter), I think this could explain the issue with the transformer... does anybody experienced the same problem?


February 25th, 2017, 01:34 AM
Power-supply's are designed to work within a range, normaly also a PET has no problems with the 233Vac.

Think you have a problem with the 5V-regulation in the power supply.
Here (http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/8032/8032029-11.gif) is your 8032 schematis

Check all outputs with a voltmeter.
Variation of the AC-power should not vary the regulated outputs.

Take Care =>Overvoltage will damage the logic, so as far as possable take out all removable logic.

If the Power-supply is repaired we will take a look at the next problem.

February 25th, 2017, 02:03 AM
We went through the same thing here. Started at 110V, went to 115V, then 120V, now 125V, which in some places measures just under 130V. A lot of antique electronics have a very hard time with this, sometimes even starting fires.

But like MauriceH says, the PET should have no problem with this relatively small deviation.

Make sure your PET is actually wired for 220V. It's happened before where someone swapped parts with another machine, or rewired a transformer, and didn't change the label. It sure sounds like it's wired for 120V.

February 25th, 2017, 02:28 AM
Get yourself a cheap multimeter (one that can read a.c. volts to 50V or so and d.c. volts to 20V or so), disconnect the transformer from the PET main board (remove the power supply connector) and measure the a.c. voltages coming out of the transformer. If this is 'alien speak' to you, say so and I will explain in more detail.

+1 for KC9UDX's suggestion of checking whether the transformer primary winding is actually for 220V or not before even plugging anything in to the mains again.


February 25th, 2017, 11:37 AM
I'd be surprised if 233V was out of spec for a 220V product, but perhaps not if it's a linear supply.

Our early-1900s 240V English Electric-based infrastructure was supposed to have been normalised to international standards but they don't appear to have done anything other than relax the overvoltage spec. It's usually 235 to 245. Plugging in old computers always makes me squirm.

We have some 220V appliances my parents brought here from 1970s Germany and ones with motors do run a bit hot.

February 25th, 2017, 02:53 PM
Linear supplies are pretty tolerant of this; think percentage. The regulator will dissipate more heat, but should still work.

February 26th, 2017, 03:02 AM
@ Paul

I put the 8032 power supply schematics in my previous post.
It is a simple with regulaturs LM340/78xx like and they have a very large input range according to the steady-output.

At most if you put in the AC-power afther a very long time 90% change to BLOW-UP your power supply.
FACT: The capacitors are That empty they are just a 100% shortage at 1st start up.
-Its a chemical device a capacitor , and a oxidelayer isolating is completly gone and have to be re-installed.
That will happen again at a SLOW start-up. fi. A resistor in series with a capacitor.

Alway's after long time start UP with reduce power starting from 0V-230V -in small steps and take at least 1 Hour Procedure.
OR: in small steps REFORM the capacitors.
Find on the internet How to "Reform Capacitors"

Unplug the Secondairy Outputs of your power supply.
a ordanairy light bulb that is meating the powerratings of your equipment in question.
PUT The Bulb in SERIES with your equipment.

Then at power up, The lightbulb will glow up and take all the voltage, Also it limmits!! the 230Vac current.
A 100% shortage of your powersupply the bulb will take it all and de Powerrating of that Bulb is the MAx current
through your psu.
So almost nothing will blow up at this time.

Start up old equipment afther long period of un-use.
90% change that it will and shall blow up.