I lost too much time to repair only one of two psu, not convenient. Better to replace only the PCB with a ATX power supply (only the PCB!)

Defect:

• Dead.

Replaced components:

• 2 x Diode IN4001
• 1 x Diode Zener 5v1
• 1 x Triac BTB 16 200B (recovered from another power supply)
• 6 x Electrolytic Capacitors.
• 1 x Power supply plug with a filter RIFA inside.

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I have repaired last year these computers for a dear friend.

Commodore 64 #1

Defect:

• Black Screen.

Replaced parts:

• Replaced 4 x 4264 RAM (U9,U10,U11,U12)

Commodore 64 #2

Defect:

• Out of Memory.
• Expansion Port (Cartridge) don’t works.

Replaced parts:

• Replaced 3 x 4264 RAM (U12,U24,U22)
• PCB track interrupted of the expansion port (A5 Address Line). Fixed with a bridge.

Commodore 64 #3

Defect:

• Garbled screen and then Out of Memory.

Replaced parts:

• Replaced 4 x 4264 RAM (U24,U12)
• Replaced 1 x 74LS257 Data Selectors/Multiplexers (U13)

Commodore 64 #4

Defect:

• Black Screen and then Out of Memory.
• No Sound.

Replaced parts:

• Replaced 2 x 4264 RAM (U9,U10)
• Replaced 1 x 74LS257 Data Selectors/Multiplexers (U25)
• Replaced 1 x 6581 SID (U18)

Read more…

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I have repaired last year these computers for a dear friend.

Commodore 128 #1

Defect:

• Black Screen.
• Missing CAS on PIN 1-4 of the 74LS32 (U9)
• Missing CHROMA video.

Fix:

• To fix the problem of lack CAS on 74LS32 i had to make a bridge from the PIN 41 of the PLA 8721 because a pcb track under the socket was interrupted.
• Broken solder joints on the RF Modulator.

Commodore 128 #2

Defect:

• Black Screen but sometimes it works.

Replaced parts:

• Replaced the socket of the 8721 PLA.
• Replaced 8721 PLA (U11).

Note:

The main problem was the PLA. In the C128 mode sometimes works and sometimes not. Works always C64 mode.

I have recovered this Terminal from the United States because it was in good condition and partially working.

The cleaning took more time of the repair. The repair was very simply. I have replaced for precaution all tantalum capacitors and i have also replaced the two micro switches that are completely rusted.

The main defect was caused by one of these two micro switches which was in short circuit always in one position. I have also made a calibration of the geometry of the screen that appeared incorrect and a focus adjustment.

Below i post all pictures of the cleaning, components replaced, various console test that i have made via terminal and two videos.

A brief introduction of the ADM-5 terminal:

The Lear Siegler ADM-5 was introduced in January, 1981 at a price of $995 and is based on the proven Lear Siegler ADM-3 design.

This new version includes:

• Numeric keypad.
• Reverse video.
• Reduced intensity video.
• Limited editing capabilities.
• Estension port.
• Lowercase display.

Lear Siegler (LSI) ADM-5 the final reult:

Replacing tantalum capacitors and mini switches:

Cleaning main pcb:

Radio Shack DT-1 (pcb) vs Lear Siegler ADM-5 (pcb):

Testing:

Video:

source:  BB ASCII Demo

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I have repaired a Commodore Amiga 2500 (A2000 Motherboard) with Black Screen for a dear friend.

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Defect:

• Black Screen.

Diagnosis:

• The Battery Acid has corroded a track (not visible to the naked eye) connected to the PIN 10 of the resistor packs RP900 and then the same track is connected to the CPU.

Repair:

• I have made a small bridge between the two points on the solder side of the pcb  and the problem was fixed in 5 minutes.

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I have fixed 3 x Commodore Amiga 4000 Motherboards and 2 x Commodore Amiga CPU Cards for a dear friend. Below the description and photo of each repair.

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Commodore Amiga 4000 Motherboard #1:

• I have done an accurate cleaning of the leaked battery acid even in the holes between pcb layers.
• Replaced some SMD electrolytic capacitors with a high ESR value.

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Commodore Amiga 4000 Motherboard #2:

• I have done an accurate cleaning of the leaked battery acid even in the holes between pcb layers.
• Replaced all SMD electrolytic capacitors with a high ESR value.

Click to view original size

Commodore Amiga 4000 Motherboard #3:

• I have done an accurate cleaning of the leaked battery acid even in the holes between pcb layers. I have also made a “bridge” because a track of the pcb was completely corroded.
• Replaced all SMD electrolytic capacitors with a high ESR value.

Still a couple of months with the battery acid and this Amiga was to throw in the trash.

Click to view original size

Commodore A3640:

• Replaced all SMD electrolytic capacitors with a high ESR value and a first acid leak.

Fixed the problem of the 3 capacitors installed with the wrong polarity. The silkscreen on the pcb are wrong. Thanks Commodore.

Click to view original size

Commodore A4CPU EC030:

• Replaced all SMD electrolytic capacitors with a high ESR value.

Atari 800XL Upgrading.

Installation and preparing:

• VBXE v2.1 Interface Installation.
• Simple Stereo + U-Switch Installation.
• Formatting and partitioning CF Card (Sandisk ULTRA 2Gb) for the SIDE 2 Cartridge/SDX.

Software update:

• Update the Ultimate 1MB (First batch 2011) Flash AM29040BL.
• Update Ultimate 1MB (First batch 2011) Xilinx XC95144XL JTAG Firmware (v1 to v2)

Upgrade/Fix:

• Fixed some wrong connections of the old installation from the Ultimate 1MB to the Atari 800XL PCB.
• Removed the RF Modulator and installation of a Female DIN (8 pin + GND) for the RGB output + RGB CTRL + SYNC + AUDIO (Stereo)
• I have also made a cable from a male DIN (8 pin) to Scart, fully shielded of a four meters lengths.

All these interfaces can be purchased on the lotharek website.

Some photos of the installation:

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I have repaired nine motherboards of the Home Computer Texas Instruments TI-99/4A for a dear friend. Below the description of each repair.

Texas Instruments TI-99/4A Repair (1 of 9)

Defect:

• Blue Screen with tiny Vertical lines and deafening sound … and then garbage screen.

Replaced parts:

• 1 x 1501392-27 ROM (U611)
• 2 x 4116 RAM (U102 / U105)
• 1 x 74LS245 OCTAL BUS TRANSCEIVER (U614)
• 1 x 74LS03 QUAD 2-INPUT NAND GATE (U506)

Texas Instruments TI-99/4A Repair (2 of 9)

Defect:

• Blue Screen with tiny Vertical lines and deafening sound.

Replaced parts:

• 1 x CD3227A ROM (U611)
• 1 x CD3226A ROM (U610)

Texas Instruments TI-99/4A Repair (3 of 9)

Defect:

• Garbage Screen.

Replaced parts:

• 4 x 4116 RAM (U105 / U106 / U108 / U109)

Texas Instruments TI-99/4A Repair (4 of 9)

Defect:

• Blue Screen with tiny Vertical lines and deafening sound.

Replaced parts:

• 1 x MCM 6810P RAM 128×8 (U609)

Texas Instruments TI-99/4A Repair (5 of 9)

Defect:

• Blue Screen with tiny Vertical lines and deafening sound.

Replaced parts:

• 1 x MCM 6810P RAM 128×8 (U608)
• 1 x 1501392-27 ROM (U611)
• 1 x 74LS138 1-OF-8 DECODER/DEMULTIPLEXER (U504)

Texas Instruments TI-99/4A Repair (6 of 9)

Defect:

• Blue Screen with tiny Vertical lines and deafening sound.

Replaced parts:

• 1 x CD3226A ROM (U610)
• 1 x 74LS138 1-OF-8 DECODER/DEMULTIPLEXER (U504)

Texas Instruments TI-99/4A Repair (7 of 9)

Defect:

• Blue Screen with tiny Vertical lines and deafening sound.

Replaced parts:

• 1 x TMS 9900-NL CPU (U600)

What happened to the other two motherboards ?

• The eighth motherboard was used for spare parts.
• The ninth motherboard has all components burned (Power Supply problem?)

The Creativision console was given to me on loan from a friend, Andrea Pierdomenico for testing the MultiROM v1.0 cartridge made by Treviso RC (Francesco Brolli)

I and Andrea we realized that the power supply was lost (tragedy). The original power supply of the CreatiVision uses 16v in AC 350ma and 9v in AC 1amp.

Here comes Ciro (Ninetyniner Iuc) that months ago gave me a transformer extirpated from a unknown motherboard and with a bit of fortune there are all voltages.

At this point, given the poor quality of the output video via antenna that comes with the Creativision i have decided to make the easy Composite Video/Audio mod and acting on the Trimmer (color gain) native on the PCB of Creativision i have reached a good quality of the image.

I must thank Andrea Pierdomenico, Ninetyniner Iuc and Francesco Brolli (Treviso RC) for the MultiROM Cartridge v1.0.

Gallery:

Repair Atari Falcon with a dead Keyboard.

Defect:

• Dead Keyboard.

Repairing:

The defect was caused by a broken track in the third layer of the pcb, thus not visible. Missing the voltage of +5v from the component (L83) towards the pin four of the keyboard connector (J18) (circuit diagram).
I have made a small bridge for fix the problem permanently.

Repairs and calibrations made:

• After a few days of normal use of the Apple /// is died the Keyboard Encoder (341-0035-00). I have replaced the chip with the Keyboard Encoder SMC KR3600-075B1 which fortunately is still available.
• Removed the filter capacitor.
• Replaced the bulb of the power-on that is embedded in the keyboard.
• Replaced all rubber feets.
• Calibration of the Floppy Drive.
• Replaced some switches of the keyboard.

Repairing keyboard Apple ///:

It seems incredible but there is always a button that doesn’t work ;-D

I found on some keyboards of the TI-99/4A the same buttons but with the plunger much smaller. I have used the plunger of the Apple /// button on the TI-99/4a button and i have fixed the problem elegantly ;-D

Thank to my friend Ninetyniner Iuc for the donation of spare parts.

Gallery:

12►

The Apple III (often rendered as Apple ///) is a business-oriented personal computer produced and released by Apple Computer that was intended as the successor to the Apple II series, but was largely considered a failure in the market. Development work on the Apple III started in late 1978 under the guidance of Dr. Wendell Sander. It had the internal code name of “Sara”, named after Sander’s daughter. The machine was first announced and released on May 19, 1980, but due to serious stability issues that required a design overhaul and a recall of existing machines, it was formally reintroduced the following autumn. Development stopped and the Apple III was discontinued on April 24, 1984, and the III Plus was dropped from the Apple product line in September 1985.

The Apple III could be viewed as an enhanced Apple II – then the newest heir to a line of 8-bit machines dating back to 1976. However, the Apple III was not part of the Apple II line, but rather a close cousin. The key features business users wanted in a personal computer were a true typewriter-style upper/lowercase keyboard (as opposed to the Apple II which was based on a teletype keyboard) and 80 column display. In addition, the machine had to pass U.S. Federal Communications Commission (FCC) Radio Frequency Interference (RFI) qualifications for business equipment. In 1981, International Business Machines unveiled the IBM Personal Computer (IBM PC) – a completely new 16-bit design soon available in a wide range of inexpensive clones. The business market moved rapidly towards the PC DOS/MS-DOS platform, eventually pulling away from the Apple 8-bit computer line.

Despite numerous stability issues and a recall that included the first 14,000 units off the assembly line, Apple was eventually able to produce a reliable and dependable version of the machine. However, damage to the computer’s reputation had already been done and it failed to do well commercially as a direct result. In the end, an estimated 65,000–75,000 Apple III computers were sold. The Apple III Plus brought this up to ~120,000. Apple co-founder Steve Wozniak stated that the primary reason for the Apple III’s failure was that the system was designed by Apple’s marketing department, unlike Apple’s previous engineering-driven projects. The Apple III’s failure led to Apple reevaluating their plan to phase out the Apple II, and eventual continuation of development of the older machine. As a result, later Apple II models incorporated some hardware, such as the Apple Scribe Printer, a thermal printer, and software technologies of the Apple III.

source: wikipedia

I have received a Commodore Amiga 500 to use as spare parts. I decided to restore because it’s a ASSY 312512 (Revision 3) with key-switch like IBM chiclet keyboards.

The cleaning took me a whole day but with a great satisfaction at the end of the work. The Commodore Amiga 500 works fine, the floppy drive reads very well and i have added a memory expansion (FAST RAM) of 512k.

Gallery of images (before and after cleaning):

Read more…

I received the Texas Instruments Expansion System (PEB) from a dear friend.

The Texas Instruments Expansion System (PEB) although fully functional, needs a restoration, for example; some parts of the top and bottom cover are rusty.

Some photos of the work that i have done:

Commodore Amiga 600 (Black Screen) Repair

Defect:

• Black Screen.

Replaced parts:

• 4 x Electrolytic Capacitor 10uF 35v
• 2 x Electrolytic Capacitor 22uf 35v

Note:

The Amiga 600 Motherboard looks in good conditions; no traces of a acid leakage from capacitors, as usually happens on Amiga 600/1200/4000, but all had a too high ESR (Equivalent Series Resistance).

Atari 7800 ProSystem (NTSC) Repair.

Defect:

• The console doesn’t power on.

Replaced parts:

• Replaced 1 x Push Button. Recovered from a PCB of an Atari 7800 that lying inside the box of the spare parts.