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The Commodore PET (Model : CBM 8096)




Photos of my CBM 8096

I obtained this machine from its original owner, it was used in a photo developing and printing business until it was retired - probably in the late '80s.

Chris had done a reasonable job of cleaning up the outside before putting it on ebay, it was in good cosmetic condition, with no evidence of the rust that I had seen on some other ebay PET/CBMs.

The keyboard was a bit grubby and a look through the cut-outs for the expansion connectors confirmed that it was not quite so pristine inside.

My first view inside a Commodore PET/CBM computer!

To get to the inside of the computer, the lid is flipped up, rather like a car bonnet - the similarity goes even further when you see the lift up support bar at the left.

In this photo, the top of the case is overextended - beyond the reach of the support bar and is actually resting on the rear of the monitor housing. The front of the case is raised about 4" off the surface of the desk that it is sat on. To allow the top to be tilted this far back, the keyboard connector has been removed.

Since last used, the machine had been consigned to an (apparently very dusty) attic.

This photo shows the edge of the hinge that allows the upper half of the case and integrated monitor to swing clear of the base.

Looking into the base of the monitor you can see the PCB for the monitor and wires between the monitor and the base - brown for AC power from the transformer and the multi-coloured wires for the VDU signals.

As you can see, a good clean was required on the inside - a thick layer of dust was covering everything, but apart from the grime, the inside also appeared to be in very good condition.

The large white plug resting on the upper PCB  is the connector for the keyboard interface cable that connects below the monitor, disconnected to allow the case to open fully.

The mains transformer is at the rear left, the 8032 motherboard is at the lower board and the extra 64k RAM card sits on top of it. 

The 64K mezzanine board is attached to the main board and chassis by four cross-head screws and the main board is attached to the base by three screws and three plastic posts.

Cleaning of the PCBs and the bottom half of the case is obviously much easier with the boards removed.

With the dust etc. removed, you can see that the metal base is in excellent condition, with hardly a blemish on it. There is a small amount of surface corrosion on the transformer and around the spot welds of the hinge support,

Solder side of the main board

The 64kB expansion RAM board
The 64kB expansion RAM board

When the machine was reassembled and powered on, it started up with an encouraging CBM 8000 series "chirp" and the screen displayed the "basic 4.0" welcome screen, but only reported "15359 bytes free".

A CBM 8096 should report "31743 bytes free", i.e., there appears to be a RAM fault on the main board.

Having found the faulty RAM, with the chip replaced, the upper 16K is now visible and the system correctly reports "31743 bytes free",

See the RAM fault repair page for the details


Photos of my CBM 8250 Dual Disk Drive

The inside of the 8250 disk unit.

Although it may not be obvious from the photo, the amount of dust inside the case was even greater than in the PET itself.

Again, a good dose of cleaning will be required, particularly inside the drives themselves to make sure that all traces of dust/debris are removed from the drive heads.

With the drives removed and the case given a good clean, you can see that, like the 8096, the chassis is in pretty good condition with no obvious corrosion present.

The power cord is terminated under the rectangular metal shroud in the upper left corner of the photo. The original power cord had been cut off close to the case, although not visible in the photo, I replaced it while I had the drives removed for cleaning.

After giving them a bit of a clean, the drives looked to be in reasonable condition for their age, but they had not actually been tested at this point.

As the photo shows, PET drives have no electronics on them, the signals from the disk sensors, motors, heads and LEDs for both drives are cabled to a common disk control board mounted on top of the right hand drive (drive 0).

A better view of the read/write heads, drive motors and the worm drive from the head stepper motors.

A small amount of corrosion is visible on the head stepper motor mounting, but does not look too serious.

The underside of the drive, showing the belt drive for the disk motor and the timing wheel fixed to the drive spindle with calibration marks for 50Hz and 60Hz.

The label shows that the drive is a Micropolis 1006-IV 

The dual disk controller board is mounted on top of the right hand drive (drive 0). 
Solder side of the dual drive controller board
Drives replaced, controller board refitted . . . . .

it's now looking a little more presentable than when I received it. 

Let's hope it works !

Time passes . . . . . . .

Well, that was a surprise, I don't have any PET disks, other than the Commodore 8250 "Demo" disk that I got with the system.

As you can see, the disk can be read - this is using drive 0, but drive 1 gives the same results.



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