Texas Instruments TI-99/4A Repair #1

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x TMS9900NL CPU (U600)

Texas Instruments TI-99/4A Repair #2

Defect:

• Wave/Raster Lines.
• Garbage on Boot Screen.

Replaced parts:

• 1 x Inductor 2 -> 4.5 μH (L100)
• 2 x TMS4116-15 RAM

Texas Instruments TI-99/4A Repair #3

Defect:

• Garbage on Boot Screen.

Replaced parts:

• 1 x MOSTEK MK4116N RAM

Video amplifier installation for Composite Video output including installation of the two female RCAs on the case.

I also made a simple fix of the metal PAD of the RESET that no longer stayed in place and consequently fell off inside the shell.

Gallery:

You shouldn’t turn on an Amiga that has been off for about thirty years without first running the usual Recap, but also following this simple rule it is not said that everything works as expected.

After the Recap i have realized that the RGB / Composite and RF output were not working properly.

From the RGB output the BLUE color was missing while the composite video and consequently RF show only a black screen.

After various measurements i came to the conclusion that the VP-101 (U30) DAC had to be replaced.

Once the DAC was replaced, the RGB output started working perfectly again, while the Composite/RF video signal they still didn’t work.

The failed component for the Composite/RF video output is the Z222 delay line, bypassing the delay line on the pins of the same one i have a “decent” composite signal but it’s not good, unfortunately this component is not easy to find, it could be solved by performing a “hack” i.e. by installing a different RGB Encoder that doesn’t need the delay lines and with some modifications on the PCB.

The game is worth the candle ? when will we use the Composite/RF video output ? probably never.

Gallery of the repair:

Commodore 64 (ASSY 250466) Repair

Defect:

• Black Screen and then Black Screen :-D

Replaced parts:

• 1 x Power Switch
• 1 x PLA 906114 (U17)

Commodore 64 (ASSY 250407) Repair

Defect:

• Garbled Screen and then No Sound.

Replaced parts:

• 2 x MOS 7708 [74LS257] (U13/U25)
• 1 x MOS 7709 [74LS258] (U14)
• 1 x MOS 6581 (U18)

Commodore 64C (ASSY 250469 REV-A) Repair

Defect:

• Garbled Screen.

Replaced parts:

• 1 x 4066 (U21)

This Amiga 1200 was sent to me by a friend to made the usual replacement of the capacitors and also overhaul everything and migrate the pcb to a new case with a new colored keyboard.

Works that have been done:

• Replacement of all electrolytic capacitors.
• Cleaning the expansion connector which was oxidized in some parts.
• General cleaning of the PCB.
• Kickstart OS3.2 installation
• Replacement electrolytic capacitor in the Panasonic JU-253-043P Floppy Drive
• Floppy Drive Cleaning.
• Greasing of Floppy Drive mechanical parts with silicone grease.
• Painting of the Floppy Disk eject button with matt Black color (Only the black button for Chinon Floppy Drive is supplied with the new case)
• CF Card adapter fixing.
• Installazione PCB and colored keyboard in the new case.
• Functioning test with Floppy Disk and CF Card.

Gallery:

12►

This drive has two different problems.

• The Floppy Drive just did not turn on.
• The motor spinning always, regardless of whether a Floppy Disk was inserted or not.

Repair:

The Floppy Drive could not work because the FUSE inside the external power supply (transformer) was missing. :-D

The second problem was caused by the RAM-I/O-Timer (RIOT) 6532 which had decided to stop working.

Replaced the RIOT and made a good cleaning and greased some mechanical parts with silicone grease, everything has started again to work better than before. :-D

Gallery of the repair:

This poor Commodore 64 already been previously repaired by me but soffer of these new problems.

• Out of Memory
• Black Screen
• No Cursor.
• Garbage screen.

The problem of the black screen at irregular intervals with the out of memory was solved by replacing the CPU 6510, as soon as the CPU warms up a little more than normal the computer displayed only a black screen, cooling the CPU still did not work but at least something was displayed.

The problem of the out of memory are 4 dead ram + 1 previously replaced and i have decided to put in a socket the remain 3.

Last problem, there was no cursor and sometimes a garbage screen was displayed, as we all know the CIA 6526 in position U1 should be faulty due to the missing cursor.

Instead of CIA 6526 it was the socket of the 6569R3, replaced the socket the cursor is back and other annoying glitches disappeared.

Commodore Floppy Drive 1541 (1540050) Repair #1

Defects:

• Drive access problems (IEC): drive resets but the computer freez with a “searching for”
• The RED led flashes twice times then stops and start again and motor runs continuously.
• The RED led flashes repeatedly every second without stopping and motor runs continuously.

Replaced parts:

• Replaced 6522 (UC3)
• Replaced 6522 (UC2)
• Replaced 901229-03 ROM (UB4)

Commodore Floppy Drive 1541 (251830) Repair #2

Defects:

• The RED led flashes repeatedly every second without stopping and motor runs continuously.

Replaced parts:

• Replaced MOS 8713 [74LS04] (UC6)

Selcom Lemon II Floppy Drive Repair and Clean.

Defect: The Floppy Drive motor spins and the LED stays on but the R/W head does not move and don’t read anythings. This is a classic failure due to incorrect insertion of the Floppy Drive connector into the male connector on the side of the Floppy Drive Controller card.

By inserting the connector moved one row externally the supply consequently go to in the wrong places and the first IC to explode in the true sense of the word is the 74LS125 (see photo).

Replaced the component, everything has started to working again.

Taking advantage of the repair, i have cleaned the inside of the LEMON II Computer and done a DUMP of the EPROM, i also cleaned and lubrificate the mechanical parts of the Floppy Drive.

Gallery of the repair:

Download: Selcom Lemon II ROM EPROM Dump (893)

2 x Atari Lynx II Repair and Recap.

The first Atari Lynx II did not turn on but when powering the console at 5v bypassing the power stage it worked properly.

I had to replace all the electrolytic capacitors and the critical components of the power stage.

• 1 x MOSFET MTDJ055E with a equivalent one.
• 2 x Transistor 2N3906.
• 1 x Zener Diode 1N5991B.
• 1 x 120 Ohm resistor.

The second Atari Lynx II working correctly so consequently i have only replaced the electrolytic capacitors.

Gallery of the repair:

Philips NMS 8245: The usual melted belt of the Floppy Drive.

Gallery:

Philips Videopac G7000 a little bit Dirty but Working. Nothing to write this time, just needed only a good clean up.

Gallery:

Dirty and Ruined Intellivision *Black Screen* repair.

It would not have been nice to put the intellivision in a very worn state and without a controller inside the spare parts box without even trying it :-)

Obviously the intellivision was not working, black screen.

The repair was simple, i have replaced the AM9114 (U8-B) RAM with a NEC 2114 and everything started working better than before :-)

I have also removed both labels in a pitiful conditions, now it looks better than before.

Gallery of the repair:

The restoration of the Sorcerer II of the Compudata (Exidy) was very simple, it was enough to replace all the tantalum capacitors with electrolytics one and make a good cleaning.

I tried the Sorcerer with the software downloadable at this link and to do a better understand the idea of the long loading (average 7 minutes) i have recorded the WAV file of the tape format on a Tape Cassette and used an old recorder to load the software, everything worked perfectly on the first try.

from Wikipedia;

The Sorcerer is a home computer system released in 1978 by the video game company Exidy.

It was comparatively advanced when released, especially when compared to the contemporary more commercially successful Commodore PET and TRS-80, but due to company focus on the coin operated video game marketplace resources were restricted for personal computer expansion and a separate division of the company was created.

Exidy Data Systems was headed by Paul Terrell to expand the product line to include small business computing with international distribution and technology license agreements to supplement corporate funding.

Distribution agreements with Dick Smith Electronics in Australia and Liveport in the UK as well as Compudata which included a manufacturing license to build, market and distribute the Tulip line of computers in Europe. Exidy sold the PC division to a Wall Street firm, Biotech, in 1983.

Gallery:

123►

Texas Instruments TI-99/4A Repair.

Defect:

• Garbage boot screen.

Replaced parts:

• 2 x TMS4116-15 RAM (U102 / U105)

Gallery of the repair: