Commodore 128 (REV 310381) Repair

Defect:

• Black Screen.

Replaced parts:

• Replaced 74LS08 (U61)
• Replaced CPU 8502R0 (U6)
• Replaced PLA 8721R3 (U11)

Gallery of the work done:

Phase5 CyberStorm MK2 @ 100Mhz (040 Hack – Stable)

This is a simple hack to overclock the Cyberstorm MK2 at 100Mhz without needed adapters or simply replacing the oscillator which causes instability or malfunctions.

The hack consists downgrading the Cyberstorm MK2 to 040 simply by moving the two resistors can you see marked in the photos.

For some CPU or MK2 models it is also advisable to replacing the original voltage regulator LT1085CM at 3.3v with this one LT912CM 3.5v but if the amiga is stable after hours of operation you can also avoid the replacing the voltage regulator.

Gallery of the work done:

source: Cosmos Blog

Commodore Amiga 4000 – 64Mb Fast Memory Hack.

The Amiga 4000 motherboard can be ´hacked´ to handle 64Mb of Fast Memory (4 SIMM modules of 16 MB each)

To do this, you have to solder a new GAL and make some bridges between FASTRAM SIMM -> GAL -> CHIP RAMSEY.

This work is not complicated but you need to have a good practice with the soldering iron and PLCC soldering.

Gallery of the work done:

Download: Amiga 4000 64Mb Hack (1738)

source: Cosmos Blog John Hertell Blog

Upgrading Commodore A3640 CPU Card (part two)

I have replaced the CPU 060 EC version with a 060 FULL with FPU REV 1.

When using the adapter with a non EC version of the 060 you must also use a fixed version of the kickstart v3.1 with the exec.library modified to support the FPU.

Gallery of the work done:

Download: Kickstart v3.1 Exec Patch Version for 3k & 4k - Ready to Burn! (1628)

Upgrading Commodore A3640 CPU Card (part one)

Works that have been done:

• Upgrading GAL (U204 & U209)
• Socket for Oscillator.
• Overclocking.
• Replacing all capacitors (the recap was already done but for the CPU adapter 040 -> 060 was necessary use smd capacitors for the little space available)
• CPU Adapter 040 -> 060.
• CPU Motorola 68EC060

Gallery of the work done:

Commodore Amiga 4000 repair with Floppy Drive that is not recognized.

Defect:

• Floppy Drive Dead (not recognized)

Repair:

• Replace CIA 8520 (U300).

Gallery of the work done:

Commodore Monitor 1084S-P Repair.

Defect:

• Completly dead with only a loud whistling noise in background.

Repair:

• Replaced the flyback transformer (AT2079/30102) everything has started to work perfectly.
• It’s mandatory to made a calibration of the SCREEN and FOCUS with the two trimmer placed on the rear side of the flyback transformer.

Note:

A loud whistling noise indicates a bad flyback transformer (also known as an LOPT).

Gallery:

Download: Commodore Monitor 1084S-P Schematics (1248)

Commodore CBM 8032 (HP – Early version 1980) – CompuThink Disk Drive Controller – External Dual Disk Drive – Woltron ROM-BUS Adapter.

• COMPU/THINK (CompuThink) Dual Disk Drive Controller with 8k RAM per commodore PET 8032 (It could be a Prototype or a Clone Board with ASSY 001-35 – DD DSK CTL COMP).
• COMPU/THINK External Dual Disk Drive 800k DD/DS.
• WOLTRON ROM (CompuThink C-DOS & TOOLKit) + PET/CBM Expansion BUS Adapter + PIA (Peripheral Interface Adapter) Motorola MC6821.

Unfortunately there is no documentation on the net of this Computhink card that seems to be a prototype or a clone, also there is no documentation or photos of the BUS/ROM Adapter by Woltron.

I spent sleepless nights looking for the starting SYS for the disk management software on the eprom, i have disassembled 24k of code (C-DOS Roms / Basic Roms Patched / Edit Roms Patched) in machine language.

I did it and found it the starting sys ($E790 – SYS 59280), although everything seems to work perfectly after the sys command is printed on the screen (*DOS-40*) and by typing the directory command ($d,1) or the format command ($f,1) the floppy starts to run correctly but the head does not move, while the exit command ($h) work correctly,
i need to say that i replaced the FDC1791 and some floppy disk logic and also one floppy disk drive, but nothing changed.

My suspicion falls on the PROM 82S123 there is no dump on the net, reading this PROM of 32 bytes, only the first 8 Bytes are filled, this is right ? we’ll never know.

All EPROM and PROM have been dumped and you can find them in the archive below.

Gallery:

Download: C-DOS 4.0 - Basic/Edit Roms Patched - PROM 82S123 (1181)

Commodore CBM 8032 (HP Early version [1980]) Motherboard Repair (ASSY 8032030)

Defect:

• Garbage screen.

Repair:

• Replaced 4 x 2114 Static RAM (UC4 / UC5 / UC6 / UC7)

Note:

As you can see from the photos this computer is already been repaired by a butcher. The butcher did not use the sockets after replacing the static ram ones and the pads had already suffered from the previous desoldering and soldering, probably using an unsuitable soldering station.

Gallery of the repair:

Commodore CBM 8032 (HP Early version [1980]) PCB Monitor Repair (ASSY 321448)

Defect:

• Dead. Missing High Voltage from Flyback Transformer (LOPT)

Repair:

• Replaced 2 x burned resistors of 56Ohm 1/4w (R752 / R753)

… and now let’s move on to the second defect. :-)

Gallery of the repair:

The SuperPET is a Commodore PET 8032 with one or two added boards that were designed at the University of Waterloo.

The computer has a built-in RS-232C interface and many programming languages on Floppy Disk. In Europe, this machine was called the MicroMainFrame 9000, or MMF 9000.

Let’s start to assembling the BMB Compuscience Ltd Board and Compu-Think 64K Memory Expansion board in the Commodore MMF 9000 (SuperPET)

I had to shorten the original standoffs installed in the computer because the length was wrong for the two boards BMB Compuscience/Compu-Think 64K. The long standoffs are used for the superPET Combo Board (the last one released).

It was not a simple job, obviously i have looked around for the identical standoffs with thickness, size, pitch and some with a long screw other with a short screw.

Between one phase and another i have also giving a nice clean inside and outside of the computer and of the motherboard.

Unfortunately there are a couple of problems after assembling the two boards of the MMF 9000 (SuperPET).

Defects:

• The keyboard space bar dead.
• Don’t runs any Waterloo program in the 6809 environment, runs only the Bootstrap menu which allows to load the programs from Floppy Disk, the Machine Language monitor and the Setup program both are in the Eprom.
• The protection Dongle (6702) not correctly viewed from the system.

Repair/Fix:

• The keyboard after a good cleaning has started to work well.
• The Dongle after cleaning the contacts now works.

About the programs that don’t runs in the 6809 environment the repair was a bit longer. I have used the only program that worked under the 6809 environment, the Machine Language Monitor.

With this program i have filled the memory with the command Fill (f 9000-9fff aa) and i have changed from time to time the bytes that i was going to write in memory and  i have used the command (d 9000-) to see the results and not all memory locations are written correctly.

With the Bank Switching command (b 0, b 1 …) i have switch the memory bank, there are 16 banks of 4k each for a total of 64k.

I have found 7 x 4116 RAM failed (this card is new, never used), replaced these bad RAMs everything has started to work properly.

So my advice is to try to load the Waterloo software in the 6809 environment to make sure that the 64k memory expansion (only seen in the 6809 environment) is working properly.

Below the photos of all the tests that i have done:

• Test with the CPU 6502 (Standard Commodore 8032/32k) with disk access, some software running in emulation 40 columns with the program: 80240.prg
• Test with the CPU 6809 of the entire Waterloo software package with disk access.

Gallery:

123►

This is a archive with documents, disk images and rom files usefully to test the computer.

Download: MMF9000/SuperPET Documents,Disk images,ROM Files (1465)

Video Composite modding:

• Removed the RF modulator.
• Removed one pin of the 3 resistors (see photo) for the video composite output, you can get a better image (contrast and color) (see photo)
• I have used the same hole of the RF cable for the composite video and audio cable.

Gallery of the Video Composite mod:

Sega Game Gear (Boxed) Full Recap.

Defect:

• Dead but the Power LED is turned ON.

Repair:

• Replaced all capacitors (Main / DC-DC / Audio)

Gallery of the repair:

Commodore 64C (ASSY 250425) Repair.

Defect:

• Basic Screen without text and prompt.

Replaced parts:

• 1 x MT 4264-20 RAM (U24)

Gallery of the repair:

Texas Instruments TI-99/4A Repair.

Defect:

• Cartridges port doesn’t work.

Fix:

• Cleaning the cartridge connector (computer side) with one pin oxided.

Gallery of the repair: