Below a short description of the repair.

Commodore PET 2001 (1977) Chiclet Keyboard (#1)

Defect:

• Garbage Screen on boot and partially in a working state.

Diagnosis/Repair:

• The Multiplexer 74LS157 (position D2) had an output (pin 4) always been in low state.

Gallery of the repair:

Commodore PET 2001 (1978) Chiclet Keyboard (#2)

Defect:

• Garbage Screen on boot.
• Memory Problems (1018 Bytes are missing)

Diagnosis/Repair:

• The garbage screen on boot was caused by a poor contact of the sockets where reside the ROMs. Temporarily fixed by inserting a precision sockets above the original socket (very bad quality sockets).
• The problem of the missing memory was fixed by replacing a RAM MPS 2114 (position J1) with a new one.

Gallery of the repair:

Defect:

• The backup system not using correctly the on-board memory and don’t load any games.

Diagnosis/Repair:

• Broken pcb track under the GAL (position U9). The battery acid has corroded some pcb tracks.
• GAL (position U9) completely dead.

Note1:

• The glitches on the screen that you see in the photo are caused by a failure on my Super Famicom. I have to fix it. ;-D

Note2:

• I don’t have the .JED code of the GAL and however i have sold many years ago my PAL/GAL programmer so i cannot replace the faulty component.

Download:

• Super Wildcard 2.8CC ROM & 2 x GAL16V8 (595)
• Super Wildcard DX (EPROM & EEPROM DUMP) (811)

Photo of cleaning (before and after):

To clean the power supply i have used compressed air and a media bristle brush.

Click to view original size

I have repaired the Commodore Amiga 2000 with a Black Screen for a dear friend.

Defect:

• Black Screen.

Diagnosis:

• The Battery Acid has corroded some pcb tracks (not visible to the naked eye) connected to the pin of the resistor packs RP900.

Repair:

• I have made three small bridges between the points on the solder side of the pcb and the problem was fixed in a short time.

I have repaired the Sharp Twin Famicom AN-500R for a dear friend.

Sharp Twin Famicom AN-500R Repair.

Defects:

• Black screen.
• Distorted sound.

Fix:

• Cold solder joints.
• Cleaning the volume slider on the second Joypad.

The microphone is mixed into the output signal, if the contacts of the volume slider are dirty you hear a background noise which disturbs the in game audio.

Gallery:

This Floppy Drive, but probably also other models, suffer of a quite annoying problem.

The little box in aluminum placed over the head of the Floppy Drive comes off, this happens because the bioadhesive foam rubber that was used to fix the “box” on the head will dry.

This piece of aluminum that at first thing can seem absolutely useless, however it is not, because it is a balancer, without this little piece of aluminum the floppy drive head vibrates and consequently don’t read / write properly.

The replacement of the bioadhesive foam rubber is very simple.

• Remove the top of the Floppy Drive (3 screws)
• Look for the little box that are detached and wanders inside the Floppy Drive.
• Thoroughly clean the remains of the bioadhesive foam rubber inside the box and on the upper side of the head (see photo). Don’t make much pressure on the head.
• Use another piece of foam rubber with the same thickness (see photo). For this purpose you can use a thousand of way to fix this box, the important thing is that must remain raised and  don’t touch the Floppy Disk (see photo)
• Fix the foam on both sides with a glue, i suggest a small amount of Bostik or Loctite – Super Attak.
• Wait for it to dry.
• Close everything.

I finally found a time to do the replacement of all the electrolytic capacitors of my Amiga 1200 that was beginning to have serious problems of stability.

Since I had disassembled the amiga i took the opportunity to do the E127R fix that solves some problems of graphics glitches with the interface Indivision AGA 1200.

The fix is very simple to do, you need to short the E127R resistor with a jumper.

I have also replaced the original power supply of the Amiga with a ATX power supply can supply more ampere and is a little stable than the original.

Commodore Amiga 1200 Recapped:

Commodore Amiga ATX Power Supply:

E127R Amiga 1200 Indivision Fix:

Click to view original size

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.

Click to view original size

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.

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?)