more lynx ii woes. please help.

[rj1307]

Well then you have bad.
If you have a jumper on like in the picture

 

 

then you can't have 12V on pin 13 U6. You may have a damaged connection between the keyboard connector and pin 13 U6 and point TP17, check it according to the pictures.

 

 

Check that the resistor R68 has 270kOhm.

 

[bobmoo79]

you were correct,  that jumper wasn't connected.  i checked and needed to resolder one of the links on because it had come loose! 

 

I checked r67 and it measures 260k in circuit.  close enough?

 

so once again I measure u6 voltages with the Atari psu connected and BOTH wire links connected as you requested. 

DVM COM connected to d11.

 

1- 9V

2- 0.3V

3- 0.3V

4- 11.8V

5- 11.8v

6- 0.1V

7- 0V (GND)

8- 0.1V

9- 11.8v

10- 0.1V

11- 10.9v

12- 12.V

13- 0.1V

14- 12V (VCC)

 

 

im not sure what you're asking me to do with u6 pin13 and tp17. I've connected those together now so perhaps that request is no longer required.

 

thanks for your patience

Edited September 20, 2019 by bobmoo79

[rj1307]

I just meant this measurement
Set the meter to measure the diodes and measure the diode D12 and D13 in both directions, i.e. first the red end of the meter on the left and then on the right. Make a note and give me the values.
Set the meter to measure resistance and measure resistor R74.
Set the meter to measure resistance and measure the value between pin 7 (GND) and pin 14 (VCC) of the U11 chip.

 

 

Edited September 20, 2019 by rj1307

[bobmoo79]

hello again,

 

DVM in diode mode:

 

d13 reads 47 in both directions. 

d12 reads 152 with COM in the left pin (red on the centre pin)

d12 reads 147 with red on the left pin (COM on the centre pin)

 

DVM set to resistance mode:

 

r74 reads 108 ohm.

u1 pin 7 and 14 reads 153ohm.

Edited September 21, 2019 by bobmoo79

[rj1307]

D13 NOK, desolder the diode and measure it outside the plate. Measure the place on the PCB where the D13 diode was.

[bobmoo79]

yes d13 didn't seem right to me so i took it off the pcb and it was definitely faulty! I hadn't checked it in a while but I'm sure when this thing went wrong it was fine, so I'm confused. maybe I didn't check it after all. 

 

anyway, I put a new one on the pcb and now with the wire jumpers in place it shows 'insert cartridge', which is fantastic news.  I inserted a cartridge and the game loads.  

 

I haven't had time to remove the wire jumpers yet but will do later. 

 

 if it doesn't power on then,  my guess is it will be a faulty flex circuit. 

 

thanks again for your help and I'll post again as soon as I have removed the jumpers. 

[bobmoo79]

so I removed the links and the lynx now appears to be working correctly(yay!) but I'm wondering why d13 failed. obviously d13 failure is BAD because it can kill the lynx and I want this to live for many years.

 

so I wonder whether the components i selected when i did the mosfet and diode replacement are correct. I thin they are but can somebody check for me??

 

here is a list of components I used during this repair. do they look ok to you?

 

or d13 I used 1N5229BTR.

 

https://uk.rs-online.com/mobile/p/zener-diodes/8050126/

 

for q12 i used AOD514

 

https://alltransistors.com/pdfview.php?doc=aod514.pdf&dire=_aosemi

 

thanks

Edited September 22, 2019 by bobmoo79

[rj1307]

The elements you have chosen are OK, although I always exchange for a 1W zener diode https://www.tme.eu/pl/details/zmd4.3-dio/diody-zenera-smd/diotec-semiconductor/zmd4-3/

You could damage the diode by soldering it to the PCB.

Check the voltage between pin 7 and 14 U11 if the voltage is 5V.

[bobmoo79]

thank you for all you help.

 

I checked the voltage on pin7 and pin 14 of U11 and it was 4.8v so this appears to be working perfectly well now.

 

I will consider changing the Zener Diode for a miniMELF 1W variety at some point but for now this one is working well enough.

 

 

[bobmoo79]

I changed to a 1w zener and it's working brilliantly.