Hello everybody.
I recently bought a CPC464 with the Board MC0044D (medium sized), and unfortunately it does not work.
I am supplying the board through the barrel connector and a lab power supply, and when i switch on the computer with the computer switch, the voltage drops suddenly to 3,7volts an flow a current of 4Amperes!!! I dont have monitor so i cant check video output for the moment, but the red led is not lighting.
In order to discard fails, i have disconnected the cassette connector, and i switched on only the board shorting pins 1 and 3 of the board connector. The result is the same, voltage drop and excessive current. So the problem is on the board.
I retired the 47uF capacitor and i tested ceramic caps so as to identify any shortcircuit, but i have not found any fail...
Looking the ic's temperatures, when i leave only the board switched on for a minute, i noticed that the 74HCU04AP and 40007 IC are hotter than the other ICs.
I measured voltage on the ics and is in general roundind 1,2Volts, very far of 5 volts...
I dont know exactly what more to check. The general status of the board is good without signals of oxide.
I am almost certain that there is a short circuit on the board, but i am a bit lost right now... Any help or orientation would be appreciated...
Thanks in advance
I am thinking if the board can be switched on without monitor and without cassette unit, supplying it through the barrel connector and shorting pins 1 and 3...
I suppose yes, specially for check voltages, but i ask here just in case the answer would be NO ;)...
Thanks!!
Quote from: neo2154 on 20:25, 05 July 23I am thinking if the board can be switched on without monitor and without cassette unit, supplying it through the barrel connector and shorting pins 1 and 3...
I suppose yes, specially for check voltages, but i ask here just in case the answer would be NO ;)...
Thanks!!
Hi, sounds like a short, and looks like you are doing all the right things. Unfortunately you do not know what has happened to it before you got it. Possibly an overvoltage but a guess. If it is follow
@eto recent thread.
Quote from: Rabs on 20:57, 05 July 23If it is follow eto (https://www.cpcwiki.eu/forum/profile/?u=3625) recent thread.
In my case, overvoltage fried several RAM ICs where at least one of them then created a short between VCC and GND:
https://www.cpcwiki.eu/forum/hardware-related/fried-my-6128-3-ohms-between-gnd-and-vcc/
Quote from: neo2154 on 20:17, 05 July 23I am almost certain that there is a short circuit on the board, but i am a bit lost right now... Any help or orientation would be appreciated...
You can measure the resistance between GND and VCC on the board to check if there is a short (or almost a short with low resistance). Then your CPC will draw whatever it gets from the power supply. It definitely makes sense to limit the current to less than 4A.
Btw: The 40007 is always hotter than the rest, that's normal.
Quote from: eto on 08:42, 06 July 23Quote from: Rabs on 20:57, 05 July 23If it is follow eto (https://www.cpcwiki.eu/forum/profile/?u=3625) recent thread.
In my case, overvoltage fried several RAM ICs where at least one of them then created a short between VCC and GND:
https://www.cpcwiki.eu/forum/hardware-related/fried-my-6128-3-ohms-between-gnd-and-vcc/
Quote from: neo2154 on 20:17, 05 July 23I am almost certain that there is a short circuit on the board, but i am a bit lost right now... Any help or orientation would be appreciated...
You can measure the resistance between GND and VCC on the board to check if there is a short (or almost a short with low resistance). Then your CPC will draw whatever it gets from the power supply. It definitely makes sense to limit the current to less than 4A.
Btw: The 40007 is always hotter than the rest, that's normal.
Good Morning.Thanks for the answers.Yesterday night, i was checking voltage and resistance in the input, and i noticed when i switch on the board a negative voltage :o
So checking the barrel input cable i was using, surprise, i was reversing the polarity :picard2:.
After set the correct polarity, the board started normally. For troubleshooting checklists it could be a classic fail :-\
I felt like Homer Simpson with monkeys in my head ;D
10 hours lost in my research. The only thing that comforts me is that the board has not apparently died in the process because of the 4Amps of current i have been injecting to the board.
I will follow reporting my results.
Thanks again...