more lynx ii woes. please help.

[bobmoo79]

so I have a lynx ii that was working until today. 

while moving it from one place to another on my desk I managed to drop it a few mm onto the desk. 

when I switched it on a few minutes later I could hear audio,  the backlight was on,  but I could only see the picture from below.

 

I switched it off then on.  this time I only got a backlight.  no display. no audio. red power led was on. 

 

switched it off and on again.  then no backlight. no display.  no audio. dim red power led.

 

switched it off and on again.  nothing.  completely dead. no power led. nothing. 

 

doesn't work with batteries or the official power supply. 

 

I took it apart to check inside.  I reflowed all recently installed caps, checked they weren't shorting etc. 

I also reflowed the new mosfet and diode. they're fine.

 

im completely stuck. given the nature of the incident I expected there to be a mechanical issue, cracked solder joint or whatever but I can't see anything and don't know where to start fault finding this thing. 

 

I find the behaviour interesting - the degraded operation over successive power cycles.  it didn't just die outright.

 

 

does anyone have any ideas? 

[power]

original screen?

 

maybe you damaged that.

[bobmoo79]

yes it's the original screen. unfortunately up until a few days ago I had a faulty spare with working backlight that I could have put in there to test but I sold it on Ebay. 

 

half that faulty screen was corrupted but it would have been good enough for testing. oh well.  

 

in this case im not sure it is the screen though.

I replaced the mosfet last night,  just in case that was at fault, but it didn't help. I then decided to check the power. with the power pack connected I got voltage on Gate and Source. nothing on the Drain.  when I press the On button nothing happens.  still nothing on Drain. 

The flex circuit was working properly,  but I guess with taking it all apart and fiddling the connection could have gone bad.  I need to check that. 

I also need to check the latch U6 to see if that's working.

just one thing to note while measuring on the mosfet I accidentally bridged the Gate and Source with the probe and I saw the backlight come on. obviously I moved the probe QUICKLY out of the way. I didn't leave it long enough to see if it would boot.  the zener is working fine - i checked that too - but I hope I didn't fry anything. 

 

I may also try adding 5v to c41 (remembering to connect 0v to c39 negative terminal) later to see what happens. 

 

Edited September 10, 2019 by bobmoo79

[bobmoo79]

ok so applying 5v to c41 worked. the lynx ii powers up and runs fine. now to figure out if the latch is working properly.....

 

 

so with power from the dc Jack,  multimeter com connected to d11, I get what appear to be the correct voltages in each pin of U6 (on button not pressed).

 

if I press the on button nothing changes and unit doesn't power on. 

 

if I briefly connect Vdd from u6 pin 14 to u6 pin11 nothing happens. unit doesn't power on. 

 

so is it safe to assume U6 is borked?

 

 

 

[+karri]

Broken U6 has happened to me once.

[sirlynxalot]

Check also to make sure the speaker is still glued to the front plastic case and not loose inside the case touching other components. Saw a repair video recently where the issue was simply the metal backing of the speaker shorting stuff out inside the lynx because it had gotten loose. 

[bobmoo79]

thanks guys. i checked the speaker and it's fine but I have the case apart right now for testing so that ruled it out anyway.

 

As for U6, well I still think it might be faulty.  im just checking around some of the power components and everything is checking out so far. 

 

if anyone has a test procedure to confirm U6 is definitely at fault  that would be brilliant. 

 

 

 

 

[bobmoo79]

got some funny readings on Q7/Q8 but they're in circuit and I didn't have time to take them out to measure them properly. 

 

im just going to replace q7, q8 and u6 and see what happens. the components are cheap so seems like a good plan.  should be here in a few days. 

[rj1307]

1. insert the cartridge and connect power to Lynx, do not press anything
2. connect the meter to pin 7 (GND) and pin 14 (VCC) of the CD4069 chip, check if it is 9V
3. Connect the meter to pin 7 (GND) and pin 11 and check if it is 0V
4. Connect the meter to pin 7 (GND) and pin 10 and check if it is 9V
5. Connect the meter to pin 7 (GND) and pin 1 and check that it is 9V
6. Connect the meter to pin 7 (GND) and pin 2 and check if it is 0V
7. press ON and check if the voltage between pin 7 (GND) and pin 1 has changed to about 4.5V
8. connect the meter to pin 7 (GND) and pin 2 and check if it is about 4.5V

 

If the voltage on pins 1 and 2 does not change after pressing ON, replace the Q8 2N3906 transistor.

[bdoi]

On 9/10/2019 at 5:27 PM, bobmoo79 said:

got some funny readings on Q7/Q8 but they're in circuit and I didn't have time to take them out to measure them properly. 

 

im just going to replace q7, q8 and u6 and see what happens. the components are cheap so seems like a good plan.  should be here in a few days. 

Do you find a working replacement part for u6?

[bobmoo79]

I followed the advice given by rj1307 above which suggested I need to change q8, so I used a q8 from a spare faulty motherboard but that didn't help.  I also fitted a CD4069UBM96 for u6 but it didn't fix my problem either so im a little confused now.  I have ordered brand new replacements for q8 and q7 so I'll try those once they've arrived.

if they don't fix it then I'm at a loss.

 

Edited September 12, 2019 by bobmoo79

[rj1307]

You can always send me and I will revive him
Do the tensions I gave agree? Do they change when you press ON on pins 1 and 2?

[+Stephen Moss]

15 hours ago, bobmoo79 said:

I followed the advice given by rj1307 above which suggested I need to change q8, so I used a q8 from a spare faulty motherboard but that didn't help.

Well it was not the best advice as it just assumed Q8 would be the issue and not any possible issue with U6, the power button, the Zenner, L15 or the MOSFET.

Personally I would use a wire to to pin 13 of U6 instead of pin 11 as that is where the power switches connect. If U6 on/off latch is working when you take pin 13 low (U6, pin 7) pin 10 should go low and stay low when you remove the the connection. Equally when you take pin 13 high (U6, Pin 14), pin 10 should go high - so start there.

 

Search for other post with things like power on/off or turn on/off in the title as power problems and how to solve them have been covered many times.

[rj1307]

You are wrong, I asked a colleague @ bobmoo79 to check the voltages on individual U6 pins in order to diagnose where the cause is, but this has not been checked. The advice was not to "replace Q8" but to check that the switching system works. 

[+-^CrossBow^-]

I've actually seen the same thing happen and it was due to the flex circuit itself. I was cleaning up the insides and recapping one of my spares a few months back. After all of that I put it back together without fully assembly in the case and it was working fine. I then remove flex circuit etc to reinstall everything back in the case and when I went to power it on, there was a brief flicker of the LCD and nothing. Turned it off and back on and now there was no LCD flicker and the power LED was very dim...barely lit at all. Took it all apart and put it back together without being in the case and eventually found that I had to wiggle the flex just right in the socket and it would power up and work properly again. 

 

So yeah...it would seem that if the flex circuit isn't in all the way in on the socket etc, it can produce some odd results as well.

 

[bobmoo79]

On 9/10/2019 at 4:38 PM, rj1307 said:

 

If the voltage on pins 1 and 2 does not change after pressing ON, replace the Q8 2N3906 transistor.

rj1307 I DID measure the voltages, they didn't change so I replaced Q8 as you suggested above. it didn't fix the problem so will check those voltages again tonight.  my new transistors turned up today so I will replace q7 and q8 if I need to. 

 

I will also follow Stephens advice,  and then if I'm still stuck I'll try the flex as suggested by Crossbow. I've been trying to avoid disconnecting the flex as it is SO fragile. I'll probably remove it,  cut off a couple of MJ and reconnect it. it's a last resort for me because it's expensive to get a replacement from the USA.

 

thanks for your help everyone

Edited September 13, 2019 by bobmoo79

[bobmoo79]

so I have now replaced u6, q7, q8, q12, d13 and the unit still doesn't power on with either batteries or official Atari lynx psi.

 

for u6 i used CD4069UBM96.

for q7 and q8 i used "40V 200mA  SOT-23 2N3906 SMD PNP Transistor"

for q12 i used AOD514

for d13 I used 1N5229BTR

 

do these all look acceptable? 

 

 

 

I have checked all resistors in the power circuit and they appear to be ok. 

I have checked all caps and none are short circuit, so i assume are ok. 

i have checked L15 and it is a short across its terminals,  so i assume it's ok. 

 

1) with the COM lead of the multi-meter on the end of D11 without the black line (furthest from C39/C41) i measure approximately the following voltages on U6...

 

Pin 1 = 12V

Pin 2 = 0V

Pin 3 = 0V

Pin 4 = 12V

Pin 5 = 12V

Pin 6 = 0V

Pin 7 = 0V (Supply)

Pin 8 = 0V

Pin 9 = 12V

Pin 10 = 12V

Pin 11 = 0V

Pin 12 = 0V

Pin 13 = 12V

Pin 14 = 12V (Supply)

 

2) connecting the top end (nearest to R70) of C38 to pin 14 of U6 for a second, the Lynx stays off when it should switch on.

 

i now measure approximately the following voltages on U6...

 

Pin 1 = 8.3V

Pin 2 = 0.5V

Pin 3 = 0.5v

Pin 4 = 12

Pin 5 = 12V

Pin 6 = 0.13V

Pin 7 = 0V (Supply)

Pin 8 = 0V

Pin 9 = 12V

Pin 10 = 0.1V

Pin 11 = 11V

Pin 12 = 12V

Pin 13 = 0V

Pin 14 = 12V (Supply)

 

so something happens but clearly this is not correct. 

 

3) if I use a piece of wire to connect the top end (nearest to R70) of C38 to the other end of C38 (or pin 7 of U6) for a second, the voltages revert back to those I measured in step 1.

Edited September 15, 2019 by bobmoo79

[bobmoo79]

I think I need some kind soul to walk me through this step by step as I'm getting nowhere fast.

[rj1307]

My suggestion is this: put on a jumper as in the picture, connect the power supply and compare the voltage on U6.

 

 

 

1- 4.6V

2- 4.4V

3- 4.4V

4- 4V

5- 4V

6- 4.4V

7- 0V (GND)

8- 4.4V

9- 4V

10- 0V

11- 8.4V

12- 8.4V

13- 0V

14- 8.4V (VCC)

 

Check R72, R73 and C43 (there is no short circuit).

 

If you have access to the cartridge socket, make a jumper instead of inserting the cartridge.

 

Edited September 15, 2019 by rj1307

[bobmoo79]

thanks for help!

 

with the jumper installed as shown in your photo, with cartridge removed, and with the atari lynx psu connected,  I get 0v on all pins of u6.

 

i tested r72, r73, c43 and none are short circuit. 

 

what's next? ?

Edited September 16, 2019 by bobmoo79

[rj1307]

Sorry, the second picture should be different:

 

 

And resistors R72 and R73 check that they have the value according to the diagram.

Edited September 16, 2019 by rj1307

[bobmoo79]

ok so here are the voltages I get now:

 

1- 12V

2- 0V

3- 0V

4- 12V

5- 12v

6- 0V

7- 0V (GND)

8- 0V

9- 12v

10- 12V

11- 0v

12- 0V

13- 12V

14- 12V (VCC)

 

Check R72, R73 and C43 are not short circuit

 

r72 is 4.7k

r73 is 10k.

 

 

thanks

[rj1307]

You don't understand me because you can't have these voltages with both jumpers unless you have a damaged path from the keyboard connector.
The first picture shows a jumper that simulates pressing the ON button. This eliminates damage to the keyboard.
The second jumper emulates the insertion of the cartridge into the socket, allows checking that the contacts in the socket are functional.
Please, put both jumpers on, connect the power supply and measure the voltage again.
Second request, can you take a photo of the U6 area?

 

 

 

Edited September 18, 2019 by rj1307

[bobmoo79]

sorry for any misunderstanding. 

 

to avoid removing the metal shield I connected positive side of c11 to c52 (nearest side to c38). this is the same as shorting pins 31 and 33 of cart connector and easier too ?

 

without a cart inserted I still get these:

(com connected to d11, then without black band):

 

1- 12V

2- 0V

3- 0V

4- 12V

5- 12v

6- 0V

7- 0V (GND)

8- 0V

9- 12v

10- 12V

11- 0v

12- 0V

13- 12V

14- 12V (VCC)

Edited September 19, 2019 by bobmoo79

[bobmoo79]

almost forgot the photo.  please ignore the red test wires.  they're only connected at one end.  the white wire connects c52 to c11.