Texas Instruments TI-99/4A Repair.
Defect:
Replaced parts:
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:
Video:
Texas Instruments TI-99/4A Repair (1 of 6)
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Texas Instruments TI-99/4A Repair (2 of 6)
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Texas Instruments TI-99/4A Repair (3 of 6)
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Texas Instruments TI-99/4A Repair (4 of 6)
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Texas Instruments TI-99/4A Repair (5 of 6)
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Texas Instruments TI-99/4A Repair (6 of 6)
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This monitor is the PAL predecessor to the Commodore 1802. It appears to be a contemporary of the CM-141 and the brown-casing 1802. They both have dual inputs (Composite video/audio, and chroma/luma/audio) with a switch in front to select between them.
The Monitor although in excellent condition don’t work correctly, the image displayed was in black and white.
The problem was the oxidation of a little trimmer (see photo / orange trimmer) and it was enough to turn it a bit and put it back in its original position.
Other small defects fixed:
Gallery:
Download: Commodore Monitor Model 1801 Instruction Manual (869)
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:
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:
source: bytedelight.com
Texas Instruments TI-99 Power Supply Repair.
Defect:
Repair:
Gallery of the repair:
DigiLog FD-2064 (C64 Floppy Drive Clone) Repair.
Defect:
Repair:
Other:
Gallery of the repair:
Download: DigiLog FD-2064 ROM (568)
After many years i have decided to made some improvements to my Sinclair ZX Spectrum 48k Issue 2.
Below what has been done:
Gallery:
Atari 2600 JR (version without RF Modulator Box) PAL Composite Video Mod for my friend Charlie.
Gallery of the work done:
source: blog.tynemouthsoftware.co.uk
Defect:
Repair:
Gallery of the repair:
When you remove a chip with the screwdriver you have to be careful to lift the chip from the socket and not the socket from the PCB :lol:
That said and after bridged the broken pcb track of the GTIA and replaced a failed RAM the computer started working properly.
After the repair i have also make a improvement of the S-Video signal (XE series support the S-Video output).
This simple mod replaces/adds some resistors and capacitors that in the XE version are wrong for a perfect S-Video signal.
The instruction can be found in the link at the end of this article.
NOTE: The description of the STEP 4 is incorrect, it’s not Q2 but Q3 and in the STEP 5 is not Q3 but Q2.
NOTE2: Obviously after assemble the computer i have noticed the “B” key was stuck, the key piston have a crack, after replace it now the button work properly.
Gallery of the repair:
Download: Svideo Atari 130XE Mod (621)
This is the same article of the previous one “Floppy Disk Cleaner” with the only difference that i have used a ALPS mechanics.
I have also connected the RED Led throught a 680 ohm 1W resistor to the 12v line.
Previous post:
Why throwing away a Commodore Floppy Disk Drive with a broken head it could become a great gadget to clean Floppy Disks.
How to do ? just disassemble the entire part that controls the movement of the head including the head itself.
The power supply used is 12v with at least 1A, you must connect the positive to the BROWN wire and the negative to the BLACK wire of the motor control PCB.
Good Cleaning.
Gallery:
This computer has kept for many years my BBS “Hidden Power / Nightfall HQ” up until closing, previously the BBS ran on the Amiga 1000 … then A500 and A2000.
I also publish two historical photos of my “BBS Room” where you can see this Amiga 3000 running.
I give a brief description of what was done and what i did today for this computer.
Everything works perfectly as you can see from the photos.
Gallery:
I received as a gift… we start badly,i have recover, we are not there, i purchased, much better, yet another computer from Radio Shack that was missing in my collection.
The computer equipped with several manuals and Floppy Disk was given to me by a dude (thanks Scott) from the United States, he had written “near mint” and is this phrase that attracted me.
The Computer is a Radio Shack TRS-80 Model 4 (GATE ARRAY) therefore of last production with cathode ray tube with green phosphors.
The seller was not joking saying that it was “near mint” and working, the computer is kept very well it almost seems like it has never been used, it can be observed from the cathode tube, from the pcb of the monitor and from the flyback transformer, keyboard, External and internal Case and from the power supply, the usual ASTEC, which has never warmed up, perfect.
The warranty sticker was also intact.
Since there was nothing to clean/repair i have made some hardware enhancements and little replacements.
What i have done:
All test are made with the FreHD interface by Ian Mavric.
Gallery:
Download: TRS-80 M4 GA Dual Boot ROM (752)
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