About 3 months ago i have repaired my Tatung Einstein with stability problems, after a few minutes the screen was filled with random characters. Below the replacement parts:
- 2 x 74LS157 (IOO6/IOO7) Multiplexer.
On the same day has broken the Tatung TC-01 Monitor, the vertical sync is died without any way of adjustment. Yesterday, instead of celebrating Easter, i have tried to repair the monitor, the faulty component was as follows:
- 1 x TDA 2578A Sync Mixer.
Very happy i have connected the Tatung Einstein to the monitor, i have tried a few games and after 15 minutes the Tatung (computer) decided to die. I spent more hours to understand what could have happened, oh! found it, some ram burned. Below the replacement parts:
- 3 x RAM 4264 (IO11/IO10/IO8)
What could happen again?
I also did the dump of the eprom (rom), the download below.
I had several problems with the repair of the Hewlett-Packard HP-85.
The first problem was the way to reconstruct the pinch roller using a latex tube, this is a very bad choice, then i have used a 10mm heat shrink, this choice instead is very good.
The second problem was the rubber parts of the pinch roller are literally dissolved and the rubber is went to cover the optical diode and part of the pcb and of course nothing has worked and the tape drive was always in stalled state.
After cleaning, the drive started to work perfectly. The last problem are the magnetic tapes 3M DC-1000 instead of HP DC-100, for the correct operation you must perform a modification by adding a resistor of 2kohm in parallel to the already present on the pcb. After this mod you need to format the tape with the “erasetape” command.
I must also thank John of the site vintagecomputers.freeserve.co.uk for the support.
Download:
source: voidware.com/calcs/hp85rep hp9845.net vintagecomputers.freeserve.co.uk
Replacement:
Simple steps to replace the keyboard Membrane of the Sinclair ZX81. The removal of the old keyboard is not illustrated but it is a very easy job.
- Open the Sinclair ZX81.
- Place the membrane.
- Remove the adhesive protection.
- Place the membrane and press firmly.
- Check the Membrane Connector.
- Gently insert the connectors on the pcb side.
- Close the Sinclair ZX81.
- Enjoy.
source: rwapsoftware.co.uk
I have repaired an motherboard of a Commodore CBM 4008 for a friend. The computer at the start-up shows only a black screen
The components that have been replaced are:
- 1 x Video Ram 2114
- 2 x SN74LS244
- 1 x 6520
The computer after the repair works perfectly. You can see from the Photo.
I have repaired an Enterprise 64 (SixtyFour) for a friend. The defect via Composite or RF was a Black Screen but with the RGB output you could see a video signals without vertical sync.
The components that have been replaced are:
- 1 x BC337
- 1 x 74LS86 (HSync/VSync to Csync)
- 1 x 74LS32 (HSync/VSync to Csync)
The computer after the repair works perfectly. You can see from the Photo.
Download: Enterprise 64/128 Schematics (1053)
source: enterprise.iko.hu
Console Amstrad GX4000 Repaired.
The fault is was caused by a wrong power connection. It was ‘resting’ the power plug of 11v on the power plug of 5v (monitor input).
Replaced parts:
The components have been recovered from the Amstrad 464+
TI-99/4A MBX Expansion System Repaired.
The interface MBX Expansion System was dead and the power voltage was in short-circuited. The failure was caused by the filter between the power supply and the 7805.
Video:
A few things to repair for a friend.
- Enterprise 64
- Archimedes 310
Defect: unknown.
I have repaired an Atari 800XL for a friend. The failure was caused by a faulty cpu, the computer freezes after 10 minutes of operation, using an oscilloscope i have noticed that the clock pin of the cpu did not give me more signal but when i have used the synthetic ice spray on the cpu has resumed to work.
This type of cpu (Atari customized 6502 – C014806-12 Sally) is not easy to find but fortunately a friend of mine (Carlo) has found a spare part for me.
Kernel JiffyDos Installation and Keyboard Repair for my friend Damiano (manosoft.it). To repair the keyboard you must clean the contacts very well on the pcb.
I received this computer to be repaired for a friend some days ago. The computer displays only a black screen and some times a random character without any sound beep at the startup boot.
I have replaced the PLA IC 324745-01 (UE5) and 324744-01 (UE6) with two EPROM 27C512 70ns (suitably programmed), the Universal PLA adapter was kindly donated by Manosoft.
The computer also had another defect, apparently the fault was not only in the two PLA. The computer starts with the classic beep but the screen remain black, the faulty is the IC 6545 (CRTC) and that was replaced.
This model uses a ROM daughterboard instead of a single 23128 ROM (EPROM 27C128 pinout compatible). I have made an adapter to preserve the original state of 8296 and allow the insertion of the daughterboard after the replacement of the two PLA that are different (in size) to the original one.
Have been replaced 4 tantalum capacitors short-circuited with 4 electrolytic capacitors. The computer has been tested and works perfectly.
I have gathered all photos of some phases of the work that i have done on the Atari 1200XL.
Below the descriptions:
- SIO 5v Enabled (you have to short-circuit the resistor R63 to get the 5v on the SIO of the Atari 1200XL)
- Repairing Keyboard (i have stretched the springs of a few keys for make the right pressure. The work must be completed using the liquid graphite where the contacts are more ruined)
I have gathered all photos of some phases of the work that i have done on the Tatung Einstein TC01.
Below the descriptions:
- Replaced 2 x 74LS157 (IOO6/IOO7) Multiplexer.
- Replaced UK Power Connector.
- Repaired some not working keys.
- External Floppy Drive 3.5″. Yes, it’s better than 3″ ;-D
Todo:
- Repair the defect of the vertical sync of the Monitor Tatung TM01
I have received this computer Commodore CBM 8296-D 1 year ago. The computer has never worked, it only displays a black screen without any sound beep at the startup boot.
The repair it was very simple, i have replaced the PLA IC 324745-01 (UE5) and 324744-01 (UE6) with two EPROM 27C512 70ns (suitably programmed). The Universal PLA adapter was kindly donated by Manosoft.
Download:
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