I received this computer to be repaired for a friend some days ago. The computer displays only a black screen and some times a random character without any sound beep at the startup boot.

I have replaced the PLA IC 324745-01 (UE5) and 324744-01 (UE6) with two EPROM 27C512 70ns (suitably programmed), the Universal PLA adapter was kindly donated by Manosoft.

The computer also had another defect, apparently the fault was not only in the two PLA. The computer starts with the classic beep but the screen remain black, the faulty is the IC 6545 (CRTC) and that was replaced.

This model uses a ROM daughterboard instead of a single 23128 ROM (EPROM 27C128 pinout compatible). I have made an adapter to preserve the original state of 8296 and allow the insertion of the daughterboard after the replacement of the two PLA that are different (in size) to the original one.

Autopsy:

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from Wikipedia:

The Commodore PET (Personal Electronic Transactor) was a home/personal computer produced from 1977 by Commodore International. A top-seller in the Canadian and United States educational markets, it was Commodore’s first full-featured computer, and formed the basis for their entire 8-bit product line.

The PET 2001 was announced at the Winter CES in January 1977 and the first 100 units were shipped later that year in October. However, the PET was back-ordered for months and to ease deliveries, early in 1978 Commodore decided to cancel the 4 kB version.

Although the machine was fairly successful, there were frequent complaints about the tiny calculator-like keyboard, often referred to as a “chiclet keyboard” because the keys resembled the gum candy. This was addressed in upgraded “dash N” and “dash B” versions of the 2001, which put the cassette tape recorder outside the case, and included a much larger keyboard with a full stroke motion. Internally a newer motherboard was used, along with an upgrade from static RAM to dynamic RAM and 8, 16, or 32 KB, known as the 2001-N-8, 2001-N-16 or 2001-N-32, respectively.

Sales of the newer machines were strong, and Commodore then introduced the models to Europe. The result was the CBM 3000 series (‘CBM’ standing for Commodore Business Machines), which included the 3008, 3016 and 3032 models. Like the 2001-N-8, the 3008 was quickly dropped.

The final version of what could be thought of as the “classic” PET was the PET 4000 series. This was essentially the later model 2000 series, but with a larger black-and-green monitor and a newer version of Commodore’s BASIC programming language.

Commodore tried to update the PET line with a new redesign called the CBM-II series (also known as the B series). These were not as successful and were ultimately abandoned. However, due to demand, the original PET machines were revived and the CBM-II case style was retained. These were known as the SK’s (due to the separated keyboard). They also had a swivel monitor. Originally, standard 8032 boards were retrofitted into these cases. Later the SK models got a new mainboard that already included the 64 kB extension directly on the board and were sold as 8296 or, with a built-in 8250 dual disk drive, as 8296-D.

source: wikipedia

Have been replaced 4 tantalum capacitors short-circuited with 4 electrolytic capacitors. The computer has been tested and works perfectly.

Autopsy:

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The motherboard is the same of Commodore VIC-1540 (Rev A/B PCB 1540007 (C) 1981 made in Japan) with a old HIGH Rom MOS “901229-03″ instead of “325303-01″.

The Commodore 1541 (aka CBM 1541, and originally called VIC-1541), made by Commodore International, was the best-known floppy disk drive for the Commodore 64 home computer. The 1541 was a single-sided 170 kilobyte drive for 5¼” disks. The 1541 followed the previous Commodore 1540 (meant for the VIC-20).

Here you can find the US version of the Commodore Single Drive Floppy Disk VIC-1541.

Testing the Floppy Drive:

I have gathered all photos of some phases of the work that i have done on the Tatung Einstein TC01.

Below the descriptions:

• Replaced 2 x 74LS157 (IOO6/IOO7) Multiplexer.
• Replaced UK Power Connector.
• Repaired some not working keys.
• External Floppy Drive 3.5″. Yes, it’s better than 3″ ;-D

Todo:

• Repair the defect of the vertical sync of the Monitor Tatung TM01