Repair Commodore 64 (ASSY 250407) 1 of 6

Asserted defect:

• Sometimes works, sometimes not, check solder.

Fix:

I state now that this Commodore 64 has been socketed.

The work done is not bad but was better clean up the remaining flux around the pcb pads, the eye wants its part.

The defect occurred twice on 55 switching on and off (i counted them)

In one of these two times i have noticed the problem that was missing the CPU Output Clock on the solder side pad. I redid the solder and fixed the socket pin and everything worked again.

I also noticed that one of the eight RAM it was warmer than the other, but working, i have decided to replace it. I don’t exclude that this operation has only fixed one of the problems, the other might to be the power supply that i don’t have.

I have twisted several times the PCB on itself, i dropped down at least 10 times on the table and leave power on for four hours, now i  can exclude solder problems.

In the photos you will see a PLA 906114 (U17) that for some bizarre reason have solder it on the socket, really curious.

Gallery of the repair:

Repair Commodore 64 (ASSY 250425) 2 of 6

Asserted defect:

• Black Screen.

Defects found:

• Missing the Composite Video Signal.
• Black Screen.
• Missing Audio.

Repair:

• Replaced 1 x MOS 8701 Clock Generator (U31)
• Replaced and Socketed 1 x MOS 906114 PLA (U17)
• Replaced 1 x MOS 6581 SID (U18)

Gallery of the repair:

Repair Commodore 64 (ASSY 250407) 3 of 6

Asserted defect:

• Black Screen.

Defects found:

• Black/Garbage Screen.

Repair:

• Replaced and Socketed 1 x MOS 906114 PLA (U17)

Gallery of the repair:

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PPI Super Sketch for Texas Instruments TI-99 Repair.

Defect:

• The cartridge is not recognized by the TI-99/4A.

Repair:

• Replaced 1 x 74LS139 (U1)
• Replaced 1 x 74LS30 (U2)

Note:

The repair of the Super Sketch cartridge was quite simple, in the first time i thought a problem of the ROM but instead the failure was the two IC U1 and U2, which should do the work of the Bank Switching.

To remove the two IC i have preferred to cut the pins and then remove each pin because i know very well this type of PCB and also lowering the temperature there is a risk that the pitches come off.

Gallery of the repair:

Easy replacement of the Commodore Amiga Mouse push-buttons.

Gallery:

ORIC-1 Repair [1 of 2]

Defect:

• Garbage boot Screen and then another Garbage screen (see photo).

Repair:

• Replaced 1 x CPU 6502 (IC5)
• Replaced 1 x RAM HM4864P (IC12)

Gallery of the repair:

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ORIC-1 Repair [2 of 2]

Defect:

• No audio.

Repair:

• Replaced 1 x Electrolytic Capacitor interrupted of 220uF 10v (C1)

Gallery of the repair:

Commodore 64 (ASSY 250407) Repair

Defect:

• Black screen and a noisy background sound .

Repair:

• Replaced 1 x MOS 906114 (PLA) U17
• Replaced 1 x MOS 6581 (SID) U18

Commodore Amiga 500 (ASSY 312510) Repair

Defect:

• Garbage boot Screen (see photo).

Repair:

• Replaced 1 x FAT Agnus 8371

Gallery of the repair:

Commodore Amiga 600 – External Floppy Drive as DF0.

This mod is very easy, just follow the schematic attached to this post.

Gallery:

Schematic:

Works that have been made:

• Cleaning the leaked acid (KONTAKT PLCC)
• Sprayed a thin layer of insulating lacquer (DUE-CI V-66)

Gallery:

2 x Texas Instruments TI-99/4 Power Supply Fixed

• Removed the RIFA Filter Capacitor, one exploded.

 Gallery:

Texas Instruments TI-99/4 Fixed

Defect:

• Garbage screen on startup immediatly or after a couple of minutes.

Fix:

• This defect is very similar to the one of the Coleco Vision console.

The problem are the pins oxidized of the power switch, i have sprayed R-11 and the problem it’s disappeared completely.

I left turned on the computer for more than 2 hours and i have made a 50 x power cycle (ON/OFF) and the problem is no longer appeared.

Note:

I thought there had to be a VDP RAM problem with a diagnosis made remotely without having the TI-99/4 in the laboratory.

To avoid using the lame RF modulator i have used a standard Commodore 64 composite cable that works very well with a NTSC composite video output.

Gallery:

Commodore 64G repaired (1 of 2)

Defect:

• Black screen

Repair:

• Replaced 1 x MOS 7707 (7406) U8

Note:

• The motherboard has been repaired several times, the technician probably in a previous life was a butcher.

Commodore 64 repaired (2 of 2)

Defect:

• Garbage screen but runs programs perfectly.

Repair:

• Replaced 1 x MOS 906114 (PLA) U17

Apple Computer 1, also known later as the Apple I, or Apple-1, was released by the Apple Computer Company (now Apple Inc.) in 1976. It was designed and hand-built by Steve Wozniak. Wozniak’s friend Steve Jobs had the idea of selling the computer.

The Apple I was Apple’s first product, and to finance its creation, Jobs sold his only means of transportation, a VW Microbus, and Wozniak sold his HP-65 calculator for $500. It was demonstrated in July 1976 at the Homebrew Computer Club in Palo Alto, California.

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Apple 1 (Mimeo / Mike Willegal Clone) Assembled for a friend of mine; Paolo Cognetti.

Many thanks for the Technical & Moral support to: Piero Todorovich and Alessandro Polito.
I also thank for some electronic components: Gabriele Molesto Zaverio of Museo Dell’informatica Funzionante, Piero Todorovich.

I had several problems with this Apple 1 clone, i very briefly describe the problems below and i attach some photos of the assembling stages.

• 1 – No video image, all voltages are ok.
• 1 + MPS3704 Transistor failure replaced with a 2N3704 pinout not compatible.

• 2 – Garbage screen during boot.
• 2 + Replaced 2 of 7 Shift Register 2504V

• 3 – Keyboard inputs not working, the WOZ monitor is freezed and shows an “@ \” but the “\” does not wrap.
• 3 + Replaced a 27k resistor half broken, probably during transport the capacitor has crushed the resistor.

• 4 – The keyboard does not respond correctly, typing A they print @, typing 1 they print 0 … and so on …
• 4 + Keyboard adapter from Apple II/+ to Apple 1 in short circuit. A wire is skewered in a pin of a Socket.

• 5 – The computer does not respond correctly, but it seems to work. The WOZ monitor responds to commands but does not write to memory and print random locations.
• 5 + Replaced a 7410 which had a pin always at high level.

• 6 – The keyboard has several problems, some switches are completly dead.
• 6 + Replaced switches.

Photos of the assembling stages:

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Video:

Commodore 64C (ASSY 250469) Repair (1 of 2)

Defect:

• Garbage Screen/Auto Load/Device not Present.

Replaced parts/Fixes:

• 1 x MOS 6526 (U1)
• 2 x Diode 1n4148 (CR9/CR11)
• Rebuilt a pcb track (see photo)

Note:

• As you can see from the photo of the the broken pcb track, evidently someone did a short circuit on the IEC connector on the data lines: SRQin and DATA.

Gallery of the repair:

Commodore 64C (ASSY 250469) Repair (2 of 2)

Defect:

• Black Screen.

Replaced parts:

• 1 x MOS 8580R5 SID in short circuit (U9)
• 2 x TMS 4464 RAM (U10/U11)

Gallery of the repair:

Commodore 64 (ASSY 250407) Repair (1 of 2)

This Commodore 64 has been already repaired in years past.

Defect:

• Grabage screen/Out of Memory.

Replaced parts:

• 5 x MT 4264-15 RAM (U10/U11/U12/U21/U23)

Gallery of the repair:

Commodore 64 (ASSY 250425) Repair (2 of 2)

Defect:

• Black Screen ..then.. Grabage screen ..then (when hot).. Screen out of Sync

Replaced parts:

• 2 x MT 4264-15 RAM (U11/U23)
• 1 x MOS 901227-03 Kernel ROM (U4)
• 1 x MOS 8701 Clock Generator (U31)

Cleaning Tape and User port connectors.

Gallery of the repair:

I have sacrificed a Floppy Disk Drive Commodore VIC 1541 to give a new look to a Floppy Disk Drive Commodore 2031 (IEEE-488).

It ‘s not been an easy job, but i’d say the result is very good.

Gallery:

Commodore Amiga 500+ (Battery Acid Leaked) Repair

Defect:

• Battery Leaks.

Components replaced and fixes:

• Battery Removed.
• Cleaned the PCB with PCC Kontakt
• Sprayed DUE-CI G-22 on all IC sockets.
• Made ten bridges to restore the traces corroded by the acid of the battery.
• Replaced 1 x 74LS244 (U12)
• Replaced 1 x 74LS373 (U13)

Gallery of the repair: