Texas Instruments TI-99/4A – 32k Internal Expansion Memory + Status LED + Reset.
Works that have been made:
- 32k Internal Expansion Memory.
- Switch for disable the Expansion Memory.
- Reset Pushbutton switch.
- Bi-Color LEDs to display the status of the internal memory expansion 32k. (ON = Green / OFF = Red)
- Replaced the resistor for the LED from 2.2k to 220 ohms.
Gallery of the works that have been made:
It could be better!
I had severals problems with the free space inside the TI-99/4a, i had to remove one side of the metal part, the biggest problem is the internal 32k expansion which is not very well done, there is no a way to secure it inside … but everything works perfectly :D
Texas Instruments TI-99/4A – F18a (FPGA Based TMS9918A) Installation.
Works that have been made:
- Installation of the F18a and removal the tape connector to make a opening for the vga connector.
- The metal cover is no longer used.
- RCA 2 DIN Homebrew Adapter to use the audio output after installing the F18a on the TI-99/4a.
Gallery of the works that have been made:
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:
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:
Defects found:
Repair:
- Replaced and Socketed 1 x MOS 906114 PLA (U17)
Gallery of the repair:
Read more…
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:
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:
As you can see this is a control pad of the Ion iCade case. It is designed to fit an iPad and has a built in stand for holding it.
The iCade is designed to work as a Bluetooth keyboard of sorts with an iPad.
It uses a standard arcade control wiring and is very easy to modify it to work with any interface can convert the signal from Analog to USB, like the PCB of a Logitech Dual Action joypad.
Gallery:
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:
Fortunately a year ago i have also updated the CPLD code (Xilinx) of the Ultimate 1MB to version v2, needed for this update!
Gallery:
source: atariage.com
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:
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
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