Texas Instruments TI-99/4A Repair.

Defect:

• Garbage boot screen.

Replaced parts:

• 2 x TMS4116-15 RAM (U102 / U105)

Gallery of the repair:

This Amiga 4000 is completely devastated on both sides of the PCB by the leaked acid of the battery and kept in a humid room for at least 20 years.

There are still a couple of things to keep, but i will do it later if necessary.

First of all, a premise: All the repairs i do are for hobby purpose ONLY. It is NOT a job, and i fix stuff for a selected people group that i consider needs my help. All other people please ask somewhere else to get your items repaired back.

A guy contacted me asking help for a repair and after an exchange of messages i agreed to repair his Amiga 4000 which at boot only displayed a Black screen.

I immediately noticed a fairly important damage caused by battery and caps acid leakage.

After cleaned everything and replaced capacitors on motherboard / 3640 and PSU (the fault persisted, of course).

Next, i used the Chucky DIAGROM: the DIAGROM is useful to understand what might be that doesn’t work, and the output via RS232 is also very useful if nothing is displayed on the screen.

Unfortunately the DIAGROM worked partially because the mouse was completely dead and therefore i have used the output via Serial but this is also worked partially because evidently also the serial is dead but in some precarious moments i  have tried to run the Sound test and no sound was reproduced.

Moral: Partially working Serial port + Mouse not working + Audio not working = Paula.

Replaced the PAULA (U400) everything started to work correctly apart the FASTRAM with 4 x 4MB SIMM modules each the system sees only 2 in the U852/U853 positions for a total of 8MB.

The problem was a short circuit probably caused by the acid leaking from the battery, i had to clean the PCB for the tenth time and the problem was fixed.

No more other to say, except that i am happy i succeeded to repaired this Amiga 4000 for a person that needed my help.

Gallery of the repair:

12►

Video:

Texas Instruments TI-99/4A Repair (1 of 6)

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x TMS 4732/2532 ROM (U610)

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 Texas Instruments TI-99/4A Repair (2 of 6)

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x MCM 6810P (128 x 8-Bit Random-Access Memory TTL/DTL) (U608)

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Texas Instruments TI-99/4A Repair (3 of 6)

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x 74LS138 (U504)
• 1 x 74LS138 (U505)

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Texas Instruments TI-99/4A Repair (4 of 6)

Defect:

• Black Screen and deafening sound in background.

Replaced parts:

• 1 x TMS 9900NL CPU (U600)

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Texas Instruments TI-99/4A Repair (5 of 6)

Defect:

• Garbage Boot Screen.

Replaced parts:

• 1 x TMS4116-15 RAM (U106)

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Texas Instruments TI-99/4A Repair (6 of 6)

Defect:

• Various problems with audio playback.

Replaced parts:

• 1 x SN76494N – Digital Complex Sound Generator (U511)

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The ZX Diag Cart by ByteDelight will visually show all kinds of details of your ZX Spectrum, which is both looking cool and useful at the same time!

It will make diagnosing defects a lot easier:

• Quickly check if voltages are present.
• If there is a dataline ‘stuck’
• If the M1 line is working…

The ZX Diag Cart automatically detects to which ZX Spectrum model it is connected, so it can control the ROM signals on ZX Spectrum 16/48K, 128K+, +2, +2A or +3, and many clones.

ZX Diag Cart Test and Sinclair ZX Spectrum 48k Issue 2 Repair:

I wanted to try this nice but also useful interface with my historical Sinclair ZX Spectrum 48k, not even doing it on purpose after several years of total inactivity the ZX Spectrum no longer worked.

The defect can i see is a total malfunction of the Basic interpreter with random errors and using the ZX Diag Cart i have see an error on all 16k RAM banks.

The voltage monitoring LEDs on the ZX Diag Cart show me that the -5v and the +12v are missing, consequently it was not a RAM problem but instead the transistor ZTX 650 (TR4)

Replaced the transistor it all work perfectly and passed all disgnostic test of the Diag Cart.

Gallery of the repair:

ByteDelight ZX Diag Cart Video:

Download:

• ByteDelight ZX Diag Cart Manual (2067)
• ZX Diiag Cart v2.15 +2A/+3 Fix (692)
• ZX Diag Cart Manual and Build Guide (917)

source: bytedelight.com

Texas Instruments TI-99 Power Supply Repair.

Defect:

• Missing 16v (AC)

Repair:

• Replaced the Thermal Fuse with one of 125° 2A (see photo).

Gallery of the repair:

DigiLog FD-2064 (C64 Floppy Drive Clone) Repair.

Defect:

• The Floppy Drive don’t read anything on the Floppy Disk (The reading led light is always off and the Head doesn’t move)

Repair:

• Replaced a 74LS10 IC.

Other:

• Dump ROM (EPROM)

Gallery of the repair:

Download: DigiLog FD-2064 ROM (630)

After many years i have decided to made some improvements to my Sinclair ZX Spectrum 48k Issue 2.

Below what has been done:

• Replaced the obsolete 7805 voltage regulator with a modern and performant one that heats up much less; the TRACO Power 2450 (DC / DC Converter)
• Replaced the ULA Ferranti with a fully compatible FPGA solution (vLA82 designed and created by Charlie Ingley). Again it does not heat anything.
• Replacement of all electrolytic capacitors.
• Rework of an old Composite MOD with a more performing one.
• Replaced the Membrane and the bioadhesive to fix the keyboard with hard keys.

Gallery:

Defect:

• Background noise (AC) and doesn’t reproduce sound from the cassette.

Repair:

• Replacement of two electrolytic capacitors of 22uf and 100uf  (see photo)
• General cleaning.

Gallery of the repair:

This repair was done only for a personal challenge, the computer is still unstable and with several died components.

After a careful cleaning the computer presents these problems:

• TED MOS 8360R2 not working (keyboard doesn’t work) even if i replace the TED doesn’t work, TED also tested on a working C16 doesn’t work.
• PIO MOS 6529 need to be replaced. The keyboard doesn’t work.
• CPU MOS 8501 Dead.
• Joystick ports (see photo)
• Cartridge connector need to be replaced.
• Modulator without lids (Above and Below)
• The sockets of TED and CPU should be replaced.
• Other rusty pieces.

Gallery of the repair:

Commodore 64 repaired ASSY 250425 (1 of 3)

Defect:

• No Video Signal.

Repair:

• Replaced 1 x MOS 8701 R1 (U31)

Commodore 64 repaired ASSY 250425 (2 of 3)

Defect:

• Out of Memory.

Repair:

• Replaced 1 x RAM MT 4264-15 (U21)

Commodore 64 repaired ASSY 250407 (3 of 3)

Defect:

• Garbage Screen.

Repair:

• Replaced 1 x RAM MB 8264A-12 (U22)

The usual modification of a Gotek in HxC this time also with OSD (On Screen Display) support for Amiga 1200.

Gallery:

Video:

source: hxc2001.com

I have received from a friend two Sinclair ZX-81 to repair and taking advantage of the “sinclair” moment :-D i have also repaired one of my ZX-81 that is died staying off for years :-(

Two out of three ZX-81 have the ULA dead, while the third had a dead membrane and some short circuits caused by someone who don’t know how to unsolder/solder properly.

I have recovered the ULA from this last one and repaired the better one of the two ZX-81, i have also installed the Video Composite mod using the ZX8-CCB kit.

I have also repaired my ZX-81 always with the ULA dead and installed the Video Composite mod using the ZX8-CCB kit.

I thank Marco Lucarelli for giving me the Video Composite mod and giving me one of the two ZX-81 (without ULA / dead Membrane and short circuits) for spare parts.

Gallery of the repair:

I have replaced all the electrolytic capacitors of this Amiga 600 motherboard.

Gallery of the repair:

I have replaced the CPU socket of the Amiga 2000 CPU because the computer have a strange boot problems, for example: black screen.

After the replacement the problem has been gone.

Gallery of the repair: