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NLG Users Repair Logs and Other Ramblings. Request your very own topic. Just ask any site staff. => Channelmaniac's Arcadecomponents' Old School Repair Logs => Topic started by: channelmaniac on September 30, 2021, 09:29:09 PM
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Model: TRS-80 Model 100
Symptom: Garbage on screen
Board had bad alkaline battery damage (Duracell)
Disassembled the computer, removed the batteries, and cleaned the mess with vinegar then rinsed / dried everything. Recapped the PCB. Patched a dead trace to fix the garbage on the screen. The screen was missing rows thanks to battery damage too. Replaced the screen with a NOS screen for a T102 and modified it slightly to work. Patched a trace to fix missing beep sounds. Removed NiCd memory backup battery and replaced it with a supercap. Tested.
NOTE: The Tandy 102 screen will work, but requires modifications as it's almost pin for pin compatible on the connector. It has the LED connections running through the cable where the T100 has the piezo beeper signals. To modify: Remove the piezo beeper from the computer. Remove the connector from the 102 screen. Cut the cable from the old display as close to the soldered connector as possible. Strip back the individual wires and solder them pin for pin to the display where the connector was removed. Cut the traces from pins 1 and 2 of the connector to the LED. Connect the wires for the LED from the T100 to the LED itself. Hot glue the piezo element to the back of the display and connect its wires to pins 1 and 2 of the connector. Test.
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Model: Leningrad 48K Spectrum Clone
Symptom: Dead. Garbage on screen
Replaced bad Z80 CPU, bad ROMs, and ROM both sockets. Resoldered bad joints on the CPU socket to fix an Address Line A8 connection. Removed a .1uf bypass cap that was incorrectly installed on the /CAS line. Removed a .1uf bypass cap was improperly installed on the RAS line. Replaced several bad Russian logic ICs. Fixed bent pin 1 on a 74LS257. Tested.
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Model: Macintosh Performa 450
Symptom: Bad caps
Replaced the caps on the motherboard and replaced one corrosion eaten pad. Replaced multiple caps in the power supply. Replaced the dead PRAM battery. Cleaned and lubricated the floppy drive and tested the computer.
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Model: Atari 800
Symptom: Dead
Replaced blown 5A slow blow fuse in the power brick. Tested.
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Model: Osborne One
Symptom: Dead
Pulled the 3 RIFA caps from board. Replaced the 2 main filter caps in the switching power supply. Replaced one shorted tantalum capacitor on the main logic board. Tested. Drive B: failed. Lubricated the worm gear shaft and spindle clamp bearing. Re-positioned a bar clamp for the bar the R/W head slid on to stop it from interfering with the head travel. Tested.
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Model: TI-99/4a PEB
Symptom: Disk errors
Cleaned drive head. Checked spindle speed. Cleaned and lubricated drive rails. Tested.
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Model: Macintosh SE/30
Symptom: Dead. Garbage on screen.
Removed leaking SMT caps. Cleaned up pads and board. Replaced corroded ROM socket and cleaned ROM SIMM contacts. Installed new SMT caps. Tested. Monitor would not focus. Analog board was OK. Rejuvenated CRT and retested. Installed Blue SCSI drive with a System 7.5.5 drive image from Macintosh Garage. Tested.
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Model: Macintosh SE
Symptom: Dead. Astec power supply restarting
Recapped the PSU. Tested - failed. Replaced 2 IRF830 transistors and 2 TO-220 cased dual diodes. Retested.
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Model: Macintosh SE
Symptom: Drive will not eject.
Cleaned / lubed drive mechanism. Replaced bad gear in eject motor assembly. Tested.
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Model: Superfo Harlequin 3H Spectrum Clone
Symptoms: Dead, no video.
Replaced bad AD724 RGB to composite video chip. Tested. Garbled screen and no sync. All the clocks were half what they should have been. Replaced 74HC00 master clock generator IC. Board would boot to 48K Spectrum ROMs and the test ROM, but would fail to boot 128 mode and fail 128 tests. Diode D3 in memory banking circuit was installed backwards. Reinstalled diode and tested. No audio. AY-3-8910 chip was counterfeit. Replaced with a chip pulled from an arcade game parts board and tested using the diagnostics ROM. Booted in 128 mode and loaded a game to test.