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Commodore Educator 64 Repair.

Defect:

• The video signal was distorted.
• Smoke coming out from the monitor.

Diagnosis:

• Short circuit in the horizontal video section.

Replaced parts:

• Replaced 1 x Diode MR 854
• Replaced 1 x Electrolytic capacitor 470uF 25v
• Replaced 1 x Resistor 1 Ohm / Tolerance 10%

Working Commodore Educator 64

Commodore Dual Drive Floppy Disk Model 4040 Repair

Defect:

• Completely dead with all LEDs lit up like a christmas tree.

Replaced parts:

• Replaced 1 x LM340K (7812) Voltage Regulator (VR1)
• Replaced 1 x 7406 Hex Inverter Buffers/Drivers (UJ6)
• Replaced 1 x 6522 (VIA) Versatile Interface Adapter (UM3)
• Replaced 1 x 6504 8-Bit CPU (UH3)
• Replaced 1 x 6502 8-Bit CPU (UN1)

Note:

The cause of many problems was the previous repair. It was replaced the voltage regulator LM340K (7812) with a LM338K (Adjustable Regulators). The two components are not compatible and have a different pinout.

Download:

• CBM 2040-3040-4040-8050 Disk Drive Manual + Led Diagnostic (1131)

I have adapted a power supply Cisco (P/N 34-0874-01) to be used with the Home Computer Amstrad CPC 6128/664 that use two voltages +5v and +12v (pinout). If you want to use this computer without the original monitor the only way is use a external power supply.

The photo speak for themselves, the modification is very simple. The only thing that i want to say, maybe not everyone knows it, the Cisco power supplies uses the STANDBY remotely, you need to connect together the ROF line with the one of two RTN (GND).

I have also added a third cable in case you want to use an external Floppy Drive.

Gallery:

Tandy Radio Shack TRS-80 Data Terminal (DT-1) Repair.

Defects:

• Some keys are dead (X – Z – DEL – ])
• Sometimes the characters typed are uppercase and sometimes lowercase.
• The DT1 Terminal doesn’t turn on the first try.
• Horizontal scan problem. The right side of the image is rolled up on itself.
• Outside ground of the CRT disconnected.

The jobs that have been made:

• Replaced 1 x 74LS138 Demultiplexer (U1)
• Replaced 1 x 74LS240 Octal Buffer/Line Driver (U23)
• Replaced almost all capacitors on the power supply side with the wrong ESR/Capacitance.
• Cleaning keyboard switches. Fortunately these switches can be opened.
• Removed the filter capacitor (RIFA)
• CRT Linearity adjustment.
• Restored the outside ground of the CRT.

Radio Shack TRS-80 Model 1 (#2) Repair.

Defect:

• Black Screen.

Replaced parts:

• Replaced 1 x CD4069 HEX Inverter (Z6)
• Replaced 1 x CD4069 HEX Inverter (Z57)
• Replaced 1 x 74LS00 QUAD 2-INPUT NAND GATE (Z5)

Radio Shack TRS-80 Model 1 Repair.

This is the second time that this computer was repaired within 2 years.

Defect:

• Video Sync issues (Horizontal Driver) and then … garbage on the screen.

Replaced parts:

• Replaced 1 x CD4069 HEX Inverter (Z6)
• Replaced 1 x MM2102 RAM (Z62)

Repair Commodore Amiga 3000 Motherboard with Battery leakage

There was once a motherboard of an Amiga 3000/25 devastated of the Battery acid where missings all the socketed components and others are unsoldered and recovered for other things.

The situation was not exactly the best one, in other words … was going into the box of spare parts.

I made the impossible, i have cleaned, scraped and rebuilt many tracks of the pcb corroded by the battery acid and i must say that with lot of patience i have repaired the motherboard giving a new life to this Amiga 3000/25 that he had no many chance to come back to work

Apple IIe Power Supply Repair.

Defect:

• Dead with clicking noise in background (This power supply works even without load)

Replaced parts:

• Replaced 1 x 200uF 10V Electrolytic Capacitor.

Removed as a precaution the RIFA filter capacitor.

Gallery:

Epson PX-4+ Easy Repair

Defect:

• Dead.

Replaced parts:

• Replaced 1 x Fuse 3A

Removed the internal Backup Battery (RB 301) 4.8v 90mA.

Commodore VIC-20 Repair

Defect:

• Black screen … then black and white image.

Replaced parts:

• Replaced 1 x 901486 KERNEL ROM (U12)
• To fix the problem of the image in black and white i have adjusted the “RED” trimmer (C48)

Commodore 16 Power Supply Repair

Defect:

• Output voltage in short circuit.

Replaced parts:

• Replaced 1 x 4700uf / 16v Electrolytic capacitor.
• Replaced 1 x 800mA Bridge rectifier.

Atari 2600 Repair

Defect:

• The second joystick port doesn’t works properly.

Replaced parts:

• Replaced 1 x 6532 RAM-I/O-Timer (RIOT)

Commodore CBM 4032 (40 Columns) Repair

Defect:

• “Device not present” error when using the IEEE 488 port (Example Floppy Drive)
• Sometimes the computer show the prompt of the TIM monitor (Machine Language Monitor program)

Replaced parts:

• Replaced 1 x IC 6522 VIA (UB15)
• Replaced 1 x IC 6520 PIA (UB16)