A4000T mouse problem

[Bokasa]

You mentioned earlier that you had 5V at F160.  So if you have 5V at F160 and there is nothing at pin 7, then there is obviously no connection between the two.

So you need to check again; is there 5V on both sides of F160 while there is not 5V at pin 7?

If the supply looks OK at F160, then follow the tracks through to the ports board.  It probably goes through a ferrite bead or low value resistor on the way, so this would be the first area of suspicion.

Definitely I have 5V at F160 and ferrite FB556 at both sides, but there's no connection between pin 7 and fb556. Stripe cables and I/O port module are OK. I can't see resistors between FB556 and PIN 7 (pin4 at 40 pins motherboard connector). Any suggestion?
Thank you very much.

[Castellen]

Definitely I have 5V at F160 and ferrite FB556 at both sides, but there's no connection between pin 7 and fb556. Stripe cables and I/O port module are OK. I can't see resistors between FB556 and PIN 7 (pin4 at 40 pins motherboard connector). Any suggestion?

Check continuity between FB556 and pin 4 of the mainboard connectors CN550 and CN560.  To find pin 4, look at the board so that the power connector P8 is in the top right hand corner.  Pin 4 of CN550/CN560 is the second pin in from the right side of the bottom row of each connector.

According to the schematic, the 5V route is F160 > FB556 > pin 4 of CN550 & CN560 > through both ribbon cables > ports module > pin 7 of joystick and mouse connectors

You may have to remove the main board from the chassis to inspect the tracks and vias on the bottom side of the board.  There may be an open circuit track if there has been an accidental short on the mouse or joystick connector, which is common if you plug a metal body connector not squarely in while the computer is on.  The problem with using polyswitch fuses for short circuit protection is that they are very slow acting, so you get high fault currents flowing for a relatively long time.  So you might find a bottom side track on the main board has fused open circuit simply because the polyswitch was too slow.

Shouldn't be too hard to find as you've mostly narrowed it down now.

[Bokasa]

Check continuity between FB556 and pin 4 of the mainboard connectors CN550 and CN560.  To find pin 4, look at the board so that the power connector P8 is in the top right hand corner.  Pin 4 of CN550/CN560 is the second pin in from the right side of the bottom row of each connector.

According to the schematic, the 5V route is F160 > FB556 > pin 4 of CN550 & CN560 > through both ribbon cables > ports module > pin 7 of joystick and mouse connectors

You may have to remove the main board from the chassis to inspect the tracks and vias on the bottom side of the board.  There may be an open circuit track if there has been an accidental short on the mouse or joystick connector, which is common if you plug a metal body connector not squarely in while the computer is on.  The problem with using polyswitch fuses for short circuit protection is that they are very slow acting, so you get high fault currents flowing for a relatively long time.  So you might find a bottom side track on the main board has fused open circuit simply because the polyswitch was too slow.

Shouldn't be too hard to find as you've mostly narrowed it down now.

I have stable 5V at F160 and FB556, and I can't find any track between FB556 and Pins4. There's small sign of corrosion (possibly capacitors leaking before replacing) at bottom side of motherboard.
Regards and many thanks

[Castellen]

I have stable 5V at F160 and FB556, and I can't find any track between FB556 and Pins4. There's small sign of corrosion (possibly capacitors leaking before replacing) at bottom side of motherboard.

Check continuity between mouse connector pin 7 and what you believe is pin 4 of CN550/CN560 to verify you have the correct pin.  If that's OK, then the track between CN550 pin 4 and FB556 is open circuit.

It's a four layer board, so it may run on an internal layer.  In which case you'll need to solder a jumper between CN550 pin 4 and FB556.  You should be able to solder directly to the via following FB556 for a tidy job on the bottom side of the board.

[Bokasa]

Check continuity between mouse connector pin 7 and what you believe is pin 4 of CN550/CN560 to verify you have the correct pin.  If that's OK, then the track between CN550 pin 4 and FB556 is open circuit.

It's a four layer board, so it may run on an internal layer.  In which case you'll need to solder a jumper between CN550 pin 4 and FB556.  You should be able to solder directly to the via following FB556 for a tidy job on the bottom side of the board.

I will try tommorow... Hope this is safe (jumpering between Fb556 and pin 4).
Thank you

[Castellen]

Hope this is safe (jumpering between Fb556 and pin 4).

That's why I said to verify what you think is pin 4 is actually pin 4.

Check continuity between mouse connector pin 7 and what you believe is pin 4 of CN550/CN560 to verify you have the correct pin.

If you connect 5V to the wrong place, the results are potentially disasterous.  However, you know that the +5V supply should be on pin 7 of the mouse port and that should be connected to CN550 pin 4.  Due to the absence of the supply voltage, you know there's a fault and have narrowed down where it is.

After you complete the repair and before you power on the computer, you should measure <2 Ohms between mouse port pin 7 and F160.

If you're not comfortable carrying out the repairs, I'm most happy to do it for you if you want to send the board to my service centre in New Zealand.

[Bokasa]

That's why I said to verify what you think is pin 4 is actually pin 4.




If you connect 5V to the wrong place, the results are potentially disasterous.  However, you know that the +5V supply should be on pin 7 of the mouse port and that should be connected to CN550 pin 4.  Due to the absence of the supply voltage, you know there's a fault and have narrowed down where it is.

After you complete the repair and before you power on the computer, you should measure <2 Ohms between mouse port pin 7 and F160.

If you're not comfortable carrying out the repairs, I'm most happy to do it for you if you want to send the board to my service centre in New Zealand.

I did it and everything works fine now! You are real wizard! Thank you very, very much!

[Castellen]

I did it and everything works fine now! You are real wizard! Thank you very, very much!

Glad to hear you sorted it out, figured it wasn't going to be overly complex.

Sadly I'm far from a wizard, only an electronics engineer.

[Bokasa]

Glad to hear you sorted it out, figured it wasn't going to be overly complex.

Sadly I'm far from a wizard, only an electronics engineer.

Oh, that is your secret... I am dramaturgist. :-)