Archive for the ‘Various’ Category

Repairing & Cleaning a Commodore CBM 610

September 29th, 2013 No comments
Characters rom & CPU 6509A

This gallery shows some stages of the cleaning and repairing the Commodore CBM 610.

Defects found on the Commodore CBM 610:

  • Black Screen of Death.
  • Garbage characters on the screen.
  • Keyboard Yellowed.
  • Filter capacitor exploded.

The black screen of death was fixed by replacing the CPU MOS 6509A and the problem of garbage characters on the screen was fixed by replacing the ROM characters with a EPROM 2532 suitably programmed.

The yellowed keyboard was replaced with a new one in good condition of the Commodore CBM 710. I like Commodore. What will be the difference of a CBM 710 and a CBM 610 keyboard? nothing, are the same! no! on the keyboard of the CBM 710 has two wires reversed! (brown/red) ;-D

The filter capacitor exploded has been removed.

Analysis & Repair of two Floppy Drives Commodore SFD-1001

September 27th, 2013 4 comments
Floppy Drives Commodore SFD-1001

This gallery shows some stages of the repairing of the two Floppy Drives Commodore SFD-1001.

Defects found on the two Floppy Drives:

  • Both floppy drives had the capacitors that leaked acid on the motor control pcb.
  • Both floppy drives had the closing arm cracked.

The difficulty was rebuild the tracks of the pcb and remove the most of the leaked acid of the capacitors. Unfortunately on the aesthetic level this type of repair are not perfect, but i’m glad that now work.

To test the correct operation of the Floppy Drives i have used a Commodore CBM (PET) 2001, and a Commodore CBM 610.

Commodore P500 (PET/CBM-II) pre-Production Prototype

September 18th, 2013 No comments
Commodore P500 (PET-II) pre-Production Prototype


I have received this computer to be repaired for a friend with a classic startup fault; the Black screen of Death.

After careful analysis of the problem and thanks to Alessandro Polito for the test, the failed component was the CPU 6509.

from Wikipedia:

The Commodore CBM-II series was a short-lived range of 8-bit personal computers from Commodore Business Machines (CBM), released in 1982 and intended as a follow-on to the Commodore PET series.

The CBM-II had two incarnations, the P series (P = personal, or, home use) and the B series (B = business use). The B series was available with a built-in monochrome monitor (hi-profile) with detached keyboard, and also as a single unit with built-in keyboard but no monitor (lo-profile). These machines were known as the “Porsche PETs” for their unique styling.

The P series used the VIC-II 40-column color video chip like the C64. It also included two standard Atari-style joystick ports. The 6509 CPU ran at 1 MHz in the P series due to the use of the VIC-II chip.

The B series used a 6545 CRTC video chip to give an 80-column “green screen” monochrome output more suitable for word processing and other business use than the VIC-II’s 40-column display. Most models have the Motorola 68B45 installed which is a pin compatible variant rather than the MOS 6545A1 2 MHz part. On the B series the 6509 CPU ran at 2 MHz.

Features common to both the P and B series included an MOS Technology 6509 CPU, an enhanced version of the venerable 6502, that was capable of addressing up to 1 megabyte of RAM via bank switching (however, no CBM-II model came with more than 256 kilobytes of RAM, 1/4 megabyte). The sound chip was the 6581 SID, the same one that was used in the popular Commodore 64 (C64) but with some limitations as it was over-clocked to 2 MHz. Additionally, the CBM-II had an industry-standard RS-232 serial interface and an IEEE-488 parallel bus (for use by disk drives and printers) just like the PET/CBM series. The CBM-II’s built-in operating system used an enhanced version of CBM BASIC version 4.0.

An optional Intel 8088-based coprocessor board allowed the CBM-II series to run CP/M-86 1.1 and MS-DOS 1.25; however, the computers were not IBM PC compatible and very little, if any, software taking advantage of this capability ever appeared. The coprocessor board only ran on hi-profile machines due to power supply and mechanical spacing requirements.

The production naming within the United States and Canada was the B128/B256 and CBM128-80/CBM 256-80 while in Europe they were known as the 600 and 700 series respectively (no “B” in front of the model number). The P machine was known worldwide as the 500 series. There are prototype models though such as the B500 (earlier B128 design) and B700 (earlier CBM 128-80/CBM 256-80 design) known to exist.

Due to the popularity of the C64, the P series was cancelled in the United States before it could be officially released; however, a few dealers who received preproduction units sold them. As these computers had not received approval from the Federal Communications Commission, this caused legal problems for Commodore. The units were recalled and destroyed, but a very small number exist today, in private collections. At least one model, the P500, was commercially released in Europe but only sold in small numbers.

source: wikipedia

Repair two Commodore CBM 8296 with Black screen of Death

September 9th, 2013 No comments

These two computers had the classic fault: Black screen of Death.

The first one was repaired by replacing a ram chip (4264) partially interrupted, the other one had One of the two chip PLA dead.

I have to thank my friend Andrea for providing me a motherboard of a 8296 for spare parts, where i have recovered the PLA which i needed.

MicroDigital TK-83 – RF (PAL-M) to Composite NTSC

August 25th, 2013 3 comments

The composite video mod for the computer Microdigital TK-83 unlike the Sinclair ZX81 it’s more easier.

You no need to install the usual transistor with 1 or 2 resistors / capacitor. The transistor is already installed on the motherboard of the Microdigital TK-83, so just pick up the video signal as described in the picture.

I remind you that the output signal will be in NTSC standard for the Microdigital TK-83 produced in Brazil (PAL-M)

Amstrad (Schneider) CPC 464 (German – Grey Keys) + Repair

August 24th, 2013 No comments
Amstrad CPC 464 (German - Grey Keys)


from Wikipedia:

The Amstrad CPC (short for Colour Personal Computer) is a series of 8-bit home computers produced by Amstrad between 1984 and 1990. It was designed to compete in the mid-1980s home computer market dominated by the Commodore 64 and the Sinclair ZX Spectrum, where it successfully established itself primarily in the United Kingdom, France, Spain, and the German-speaking parts of Europe.

The series spawned a total of six distinct models: The CPC464, CPC664, and CPC6128 were highly successful competitors in the European home computer market. The later plus models, 464plus and 6128plus, efforts to prolong the system’s lifecycle with hardware updates, were considerably less successful, as was the attempt to repackage the plus hardware into a game console as the GX4000.

The CPC models’ hardware is based on the Zilog Z80A CPU, complemented with either 64 or 128 kB of memory. Their computer-in-a-keyboard design prominently features an integrated storage device, either a compact cassette deck or 3″ floppy disk drive. The main units were only sold bundled with a colour or monochrome monitor that doubles as the main unit’s power supply. Additionally, a wide range of first and third party hardware extensions such as external disk drives, printers, and memory extensions, was available.

The CPC series was pitched against other home computers primarily used to play video games and enjoyed a strong supply of game software. The comparatively low price for a complete computer system with dedicated monitor, its high resolution monochrome text and graphic capabilities and the possibility to run CP/M software also rendered the system attractive for business users, which was reflected by a wide selection of application software.

During its lifetime, the CPC series sold approximately three million units.

Replacement/Adaptation of a power switch for Amstrad CPC 464:

source: wikipedia

Eprom Motorola MCM68766C replaces the C64/VIC-20 Rom

August 16th, 2013 No comments
Promenade C1 Eprom Burner

If you are the lucky owners of these eprom: Motorola MCM 68766C you can do something really cute, hardware permitting. Example: use this EPROM like a ROM for some Devices and Computers Commodore without using an adapter ;-D

I had to use the EPROM programmer Promenade C1 for Commodore 64 to burn these eprom because all my programmers don’t support these type of eprom.

Download: Eprom Motorola MCM68766C Datasheet (1139)

Restoration and Repair of a Sinclair Spectrum 128k +2A Arabic Version

August 11th, 2013 4 comments
Sinclair Spectrum 128k +2A (Black) Arabic Version


This is the translation of the Arabic boot screen:

© 1987, 1988 Sinclair of Egypt
presented by Matsico Corp, an authorized dealer of Sinclair & Amstrad in Egypt
prepared by Dr. Nabil Nazmi
(Version 3)

The computer is arrived in pitiful condition. The inside of the computer and the keyboard were are full of sand and dirt.

Restoration and repairs that have been made:

  • Replaced the top case with a new one.
  • Replaced the bottom case with a new one, then replaced again with the old one to keep the original appearance. (the hole for the switch is standard in the Arabic version)
  • Replaced the tape recorder.
  • Replaced the motherboard with a issue #2 instead of issue #1 (was not convenient the repair)
  • Cleaned all keys and membrane.
  • Replaced all rusty springs of the keyboard.
  • General cleaning.
  • Moved the ROM/EPROM mod on the new motherboard.
  • Replaced the original switch with a new one, then replaced again with the old one to keep the original appearance.

from Wikipedia:

The ZX Spectrum +2 was Amstrad’s first Spectrum, coming shortly after their purchase of the Spectrum range and “Sinclair” brand in 1986. The machine featured an all-new grey case featuring a spring-loaded keyboard, dual joystick ports, and a built-in cassette recorder dubbed the “Datacorder” (like the Amstrad CPC 464), but was in most respects identical to the ZX Spectrum 128. The main menu screen lacked the Spectrum 128′s “Tape Test” option, and the ROM was altered to account for a new 1986 Amstrad copyright message. These changes resulted in minor incompatibility problems with software that accessed ROM routines at certain addresses. Production costs had been reduced and the retail price dropped to £139–£149.

The new keyboard did not include the BASIC keyword markings that were found on earlier Spectrums, except for the keywords LOAD, CODE and RUN which were useful for loading software. This was not a major issue however, as the +2 boasted a menu system, almost identical to the ZX Spectrum 128, where one could switch between 48k BASIC programming with the keywords, and 128k BASIC programming in which all words (keywords and otherwise) must be typed out in full (although the keywords are still stored internally as one character each). Despite these changes, the layout remained identical to that of the 128. The ZX Spectrum +2 power supply was a grey version of the ZX Spectrum+ and 128 power supply.

The ZX Spectrum +2A was a variant of the Spectrum +3 housed a black version of the Spectrum +2 case mouldings. The Spectrum +2A/+3 motherboard (AMSTRAD part number Z70830) was designed such that it could be assembled without the floppy disk controller or associated logic and a +2 style “datacorder” connected. Originally, Amstrad planned to introduce an additional disk interface for the +2A/+2B called the AMSTRAD SI-1, however this never appeared. If an external disk drive was added, the “+2A” on the system OS menu would change to a +3.

The power supply of the ZX Spectrum +2A used the same pinout as the +3. However, the power supply purchased with the +2A/B had “Sinclair +2″ written on the case.

source: wikipedia

Apple ][ Europlus (Apple II Europlus) Restoration and Repair

July 31st, 2013 1 comment

This gallery shows some stages of cleaning the computer Apple ][ Europlus, Apple Disk ][.

I have also made minor repairs which i describe below:

  • Replaced the Lamp of the power-on.
  • Removing the RIFA filter capacitor (the capacitor was exploded)
  • Fixed the center hub of the Apple Disk ][.

CBS ColecoVision: diagnosing and fixing motherboard faults

July 26th, 2013 No comments

I have decided to repair my Coleco Vision Secam version (RGB) purchased some years ago in a full working state, today is died. Below a description of the defect and of components being replaced.

Defect: dirty sprite

  • 3 x 4116 (RAM)

MicroBee PC 85 (Model II) Keyboard Repair

July 24th, 2013 No comments

I have received this computer in excellent cosmetic condition but unfortunately with some dead keys of the keyboard.

The trick of the repair is cleaning the two little strips and the small conductive button (see the photos)

Some spare parts from a Friend

July 21st, 2013 No comments

I have received from a friend a couple of components that can be used as spare parts for the repairs. Thanks Andrea.

Close-up description:

  • 1 x Commodore CBM 4040 Dual Floppy Disk Drive PCB
  • 1 x Commodore CBM 8050/8250 Dual Floppy Disk Drive PCB
  • 2 x Texas Instruments TI-99/4A PCB
  • 1 x Main powersupply of Commodore CBM 4040/8050/8250 Dual Floppy Disk Drive.
  • 1 x Sinclair ZX Spectrum+
  • 1 x Sony HB-10P MSX

Philips Videopac G7000 (PAL) RGB Video Mod

July 20th, 2013 7 comments
Philips Videopac G7000 with RGB Output


I have found this RGB mod for the Philips Videopac G7000 console fom the gamesx site and i have decided to build the circuit to see if it works.

This mod is not easy to do, especially if one has no experience in electronics, however the result at the end is spectacular.

RGB DAC Schematics (click to zoom):

Download: Philips VideoPac G7000 Schematics (987)


Commodore CBM 8050 Cleaning and Repair

July 14th, 2013 1 comment

This gallery shows some stages of cleaning the Commodore CBM 8050 Dual Drive Floppy Disk. Below the defects and replacement parts.


  • Died – Status LED: RED (5 Flash) Zero page error.

Replacement parts:

  • 1 x 6502
  • 1 x 6532
  • 1 x 6522
  • The connectors of write enable sensors are inserted incorrectly.
  • Missing +5v on the PCB of the sensor circuit.
  • Dirtiness in the write enable sensor drive 0
  • Cleaning floppy drive heads.
  • Cleaning belt of the floppy drive.
  • Removing the filter capacitor.
  • The Analog PCB of the Floppy Drive is not fixed properly.
  • The Locking screws of the external box are not original.
  • Lost the felt which push the Floppy Disk vs the head.
  • Disk is present (Switch Motor) dirty.
  • General Cleaning.

Test formatting floppy disk:

CBS ColecoVision: diagnosing and fixing motherboard faults

July 1st, 2013 1 comment

I have decided to repair my two ColecoVision consoles bought like non-functioning many years ago. Below a description of the defects and of components being replaced.

Defect: black screen

  • 1 x 2114 (VRAM)
  • Joystick port # 1 broken (replaced with the joystick port of a Texas Instruments TI-99/4A)

Defect: black screen

  • 1 x 2114 (VRAM)
  • 3 x 4116 (RAM)