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:

Repair Apple II EuroPlus.

This computer has taken a lot of moisture and temperature changes, it can be seen because the connectors (Apple BUS) have dried up and the plastic tends to break. In addition, some pins of the ICs are rusty, fortunately few.

The main problem of this computer, as well the removal of the usual filter capacitor inside the power supply, was that don’t accepts some basic commands (see photo)

The problem was caused by the malfunction of the PROM 341-0014. (E8)

The owner will have to decide whether to purchase the original PROM (current price €13,90 + Shipping) or use a horrible adapter to insert an EPROM 27C16 (2716) in place of a PROM.

This adapter in addition to changing the aesthetics of the original motherboard brings with it some problems.

• 16k language card don’t work.
• Long cards which extend to the part of the circuit board cannot be used.

Gallery of the repair:

source: willegal.net classic-computers.org.nz

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:

This Commodore 64 was found in the trash from a friend, although aesthetically in a good state, the computer doesn’t work.

Defect:

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.

Click to view original size

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…

Clicca per ingrandire l’immagine

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

Click to view original size

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

Click to view original size

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.

Click to view original size

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.

Click to view original size

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:

12►

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?)