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:

Jean-François DEL NERO (who’s behind the HxC SD Floppy Emulator) recently has released a version of the HxC emulator firmware that is compatible with the STM32 chip used in the Gotek floppy emulators.

This means that the great functionality of the HxC SD emulator is now available on cheaper and more widely available hardware.

The bootloader to convert the Gotek floppy drive in HxC compatible must be purchased on the website HXC 2001 by sending an email to Jean-François DEL NERO. The price of the bootloader is one-off 10 Euro per Gotek that you want to update. Future updates of the software are free and can be made from a USB stick

The HXC Usb (Gotek) firmware supports:

Flashing the Gotek floppy emulator with HxC firmware:

Gotek floppy emulator with HxC firmware (Testing on Amiga Computer):

Gotek floppy emulator with HxC firmware (Testing on Amstrad CPC computer):

Gotek floppy emulator with HxC firmware (Testing on Atari ST Computer):

Gotek Audio Track Loader:

The schematics is here

Components:

• 1 x Buzzer.
• 1 x BC547 or similar bipolar transistor.
• 1 x 1k resistor.

I have to thank Jean-François DEL NERO for the support that he gave me for the bootloader programming.

source: hxc2001.com

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 (432)
• Super Wildcard DX (EPROM & EEPROM DUMP) (562)

Explanation of how it work the program “RAM3_RAMFAIL_BAS” written by Dominic Brown in the 1990 in Super Basic for the Sinclair QL which is used to calculate what the RAM on the Sinclair QL is broken, you need to use the MINERVA ROM (RAM PassCheck).

I tried to explain how it work and i have rewrote the software in a “language” a bit more modern ;-D

MINERVA OUTPUT EXAMPLE:

——————————————
WRITE: 5 4 8 C 4 8 7 8
READ: 5 C C D 5 C C D
ADDRESS: 0 0 0 3 2 0 0 0
——————————————

HEX WRITE: 54 8C 48 78
HEX READ:  5C CD 5C CD

Convert the numbers in decimal:

DECIMAL WRITE: 84 140 72 120
DECIMAL READ:  92 205 92 205

You have to make a xor in pairs (write & read)

XOR: 84 XOR 92 = 8
XOR: 140 XOR 205 = 65
XOR: 72 XOR 92 = 20
XOR: 120 XOR 205 = 181

Now you need to do an OR with the result of the XOR starting with “0″ and continuing with the result of every OR

OR: 0 OR 8 = 8
OR: 8 OR 65 = 73
OR: 73 OR 20 = 93
OR: 93 OR 181 = 253

Convert the final result of the OR in Binary.

DECIMAL: 253
HEX: FD
BINARY: 11111101

Follow the table to find the faulty ram. Pay attention to the memory address.

1: BAD Ram
0: GOOD Ram

BINARY = 1     1     1     1     1     1     0     1

IF < $30000 (ADDRESS) = IC8  ,IC7  ,IC6  ,IC5  ,IC4  ,IC3  ,IC2  ,IC1

IF > $30000 (ADDRESS) = IC16 ,IC15 ,IC14 ,IC13 ,IC12 ,IC11 ,IC10 ,IC9

IF > $40000 Faulty ram is in expansion memory.

The Original Program (ram3_ramfail.bas) was written for the SINCLAIR QL in SUPER BASIC language by Dominic Brown (1990).
Documentation of how it work by Xad/Nightfall (2015).
Thanks to my friend for the support.

Faulty Ram Decoder Changelog:

• v0.1: First Release.
• v0.2: Added a message (Faulty ram is in expansion memory) if the Address > $40000.

Faulty Ram Decoder Online: http://www.nightfallcrew.com/minervaram

Download:

• Faulty Ram Decoder v0.1 PHP Script (1063)
• Faulty Ram Decoder v0.2 PHP Script (1110)

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