Lynx 2 Power Issue

[ThatGuyUKnow]

Hello all! I have an Atari Lynx 2 that was fully working before I replaced Q8/9 transistors, Q11 MOSFET and D1 zener with the Console5 set. The system will no longer power on.

 

I injected 5V into C41 and it boots up correctly which tells me the issue is with the power system. It’s likely not relevant, but I did recap the system as well. 

 

I replaced the transistors, mosfet, and diode again with no change.

 

 

Ive gone through some of the old forum posts to diagnose the issue and took some readings. 
 

Regarding U6: 

With the DMM common on Ground the readings are as 

1: 0

2: 8.9

3: 0

4: 0

5: 8.9

6: 8.9

7: 8.9

8: 8.9

9: 0

10: 0

11: 8.8

12: 8.8

13: 0

14: 8.1

 

With Com on pin 7:

1: .453

2: 0

3: 0

4: Starts at about 1.7V then moves to about 200mV

5: 0

6: 0

7: COM

8: 0

9: 0

10: .457

11: 0

12: 0

13: Starts at about 2.6V then moves down to about .433V

14: .433

 

I checked the system with a thermal cam and didn’t find any hotspots.

 

TP 15 is 0V.

If I connect the drain and gate on the mosfet the system powers up.

 

Thoughts?

 

 

[+-^CrossBow^-]

You are sure that you placed the new diode in the correct position? Remember the black band faces towards TP19. I've done that more than once myself when not paying enough attention.

[ThatGuyUKnow]

Yes it’s pointed to TP19.  I tried with the zener shown on the board as well as the one that came with the Console5 set. Same result with both.

[ZLevee]

Not a bad suggestion @-^CrossBow^-. I’ve seen some good past power troubleshooting from@rj1307, @karri, @Stephen Moss, @cowdog360 - any thoughts guys?

Edited June 14, 2021 by ZLevee

[+Stephen Moss]

14 hours ago, ThatGuyUKnow said:

Hello all! I have an Atari Lynx 2 that was fully working before I replaced Q8/9 transistors, Q11 MOSFET and D1 zener with the Console5 set. The system will no longer power on.

 

I injected 5V into C41 and it boots up correctly which tells me the issue is with the power system. It’s likely not relevant, but I did recap the system as well. 

 

I replaced the transistors, mosfet, and diode again with no change.

 

 

Ive gone through some of the old forum posts to diagnose the issue and took some readings. 

First, as the old saying goes, "if it ain't broke, don't fix it". That aside, you did not indicate if the listed voltages are when the Lynx is off (as in after the power source is connected & the On button has not pressed) or after the On button was pressed which makes it a little difficult to be certain which (if any) voltages are correct not knowing which state to compare them against.

However, the following pins of U6 should be connected and therefore at the same voltage...

2 & 3

4, 5 & 9

6 & 8 

10 & 13

11 & 12

but you measurement with DMM common on GND shows that is not always the case suggesting that either you have some bad solder joints, made an error in your measurements or there is a problem with U6 (assuming you had a cartridge inserted).

Your measurements with the DMM common on pin 7 of U6 are a little more consistent in terms of pins that should be at the same voltage are but you are reading essentially no voltage anywhere, that suggests to me that you may not have a good power connection connection to U6. Try performing a continuity test from the power pins to the battery terminal to verify, if that is part of the issue from the measurements given I think it more likely the problem lies with GND connection than VSS but best to check both. But take into account that the meter probe contact may create the connection so try to use as little pressure as possible on the pins, alternatively try re-soldering them. 

 

You also state that TP15 is 0V, that should never be the case unless there is a brake in the power rail. Once a power source is connected TP15 should either be 12-14V (PSU and Lynx off) or 9V (PSU Lynx On/Battery, Lynx on or off) when measured with respect to power GND (left of Q12 on the schematic). If you were measuring with respect to the single point GND (right of Q12) then I would expect a reading of 0V if taken while the Lynx is off.

 

You also mentioned connect the Drain and Gate powered the Lynx are you sure it was Drain and Gate rather than Source and Drain? How the latter would work is obvious but not something i would suggest doing for long as the entire system will be running at 9V.  Whereas with Drain and Gate I cannot see where there would be a sufficiently high current path to GND for that to work.

[ThatGuyUKnow]

On 6/14/2021 at 4:24 AM, Stephen Moss said:

First, as the old saying goes, "if it ain't broke, don't fix it". That aside, you did not indicate if the listed voltages are when the Lynx is off (as in after the power source is connected & the On button has not pressed) or after the On button was pressed which makes it a little difficult to be certain which (if any) voltages are correct not knowing which state to compare them against.

However, the following pins of U6 should be connected and therefore at the same voltage...

2 & 3

4, 5 & 9

6 & 8 

10 & 13

11 & 12

but you measurement with DMM common on GND shows that is not always the case suggesting that either you have some bad solder joints, made an error in your measurements or there is a problem with U6 (assuming you had a cartridge inserted).

Your measurements with the DMM common on pin 7 of U6 are a little more consistent in terms of pins that should be at the same voltage are but you are reading essentially no voltage anywhere, that suggests to me that you may not have a good power connection connection to U6. Try performing a continuity test from the power pins to the battery terminal to verify, if that is part of the issue from the measurements given I think it more likely the problem lies with GND connection than VSS but best to check both. But take into account that the meter probe contact may create the connection so try to use as little pressure as possible on the pins, alternatively try re-soldering them. 

 

You also state that TP15 is 0V, that should never be the case unless there is a brake in the power rail. Once a power source is connected TP15 should either be 12-14V (PSU and Lynx off) or 9V (PSU Lynx On/Battery, Lynx on or off) when measured with respect to power GND (left of Q12 on the schematic). If you were measuring with respect to the single point GND (right of Q12) then I would expect a reading of 0V if taken while the Lynx is off.

 

You also mentioned connect the Drain and Gate powered the Lynx are you sure it was Drain and Gate rather than Source and Drain? How the latter would work is obvious but not something i would suggest doing for long as the entire system will be running at 9V.  Whereas with Drain and Gate I cannot see where there would be a sufficiently high current path to GND for that to work.

Yes those were voltages with the power plugged in, game inserted, and no power button pressed before measurements were taken.

 

I thought the same thing regarding the U6 being faulty so I replaced it with a MC14069B U6 replacement chip from eBay.

 

Still getting weird readings.

 

double checked TP15 and with the AC plugged in I’m getting .450V.

 

 

Regarding the power pins to the battery terminals, these were the DMM continuity/resistance readings with no power.

 

- Batt Terminal.
Pins 2+3 have direct connection .8 Ohms.

OL for pin 1

 

+ Batt Terminal

pin 2 4.8M Ohms

pin 1 2.3M Ohms

pin 3 2.3M Ohms

 

Looking at the schematic: I wanted to check the power rail. Continuity from pin 1 to anode. Using diode mode .555V anode to cathode, OL cathode to anode.

I used the cathode as the continuity point for the rest of the power rail. 

 

Continuity to cathode of D11 .535V anode to cathode, 2.5V cathode to anode. Continuity to C35, C36, C39 positive, D12  cathode, continuity to C40, C41 positive, continuity to the emitter on Q8, continuity to R74, C44, and R75.

 

Does anything stick out to you here or should I check through the ground rail?

 

Jared 

 

[+Stephen Moss]

6 hours ago, ThatGuyUKnow said:

Regarding the power pins to the battery terminals, these were the DMM continuity/resistance readings with no power.

 

- Batt Terminal.
Pins 2+3 have direct connection .8 Ohms.

OL for pin 1

 

+ Batt Terminal

pin 2 4.8M Ohms

pin 1 2.3M Ohms

pin 3 2.3M Ohms

I think there was some misunderstanding here, I was referring to the power pins of U6 as the symptoms you were describing were suggestive that one of its power pins was not connected.

It would not hurt to check continuity through the GND rail, just to be sure.

 

6 hours ago, ThatGuyUKnow said:

Looking at the schematic: I wanted to check the power rail. Continuity from pin 1 to anode. Using diode mode .555V anode to cathode, OL cathode to anode.

I used the cathode as the continuity point for the rest of the power rail. 

 

Continuity to cathode of D11 .535V anode to cathode, 2.5V cathode to anode. Continuity to C35, C36, C39 positive, D12  cathode, continuity to C40, C41 positive, continuity to the emitter on Q8, continuity to R74, C44, and R75.

Generally, continuity seems to be OK from the above with the exception the you have specified some continuity which is a resistance measurement as voltages. So I am a little puzzled as to why you are not reading the correct voltage at TP15. Maybe you just have a bad connection to TP15 in which case you could try measuring to the top end of R74, or R75 and see what you get there.

6 hours ago, ThatGuyUKnow said:

double checked TP15 and with the AC plugged in I’m getting .450V.

You are measuring this as a DC voltage right? If you were measuring it as AC that could also explain the apparent lack of voltage, if you were measuring at as DC try it with Battery power. With the COM lead of your meter on Pin 7 of U6 you should measure the same battery voltage at Pin 1 of the battery connector, Pin 14 of U6 and TP15. 

[ThatGuyUKnow]

On 6/21/2021 at 4:18 AM, Stephen Moss said:

I think there was some misunderstanding here, I was referring to the power pins of U6 as the symptoms you were describing were suggestive that one of its power pins was not connected.

It would not hurt to check continuity through the GND rail, just to be sure.

Pin 2 continuity to L14, continuity to both sides of L14 inductor, L14 continuity to anode of D10, D10 anode continuity to D11 anode, D11 anode continuity to C35, C35 continuity to C37 ground, C35/C37 continuity to R68,

 

no continuity to C52 (I can't pass voltage in diode mode, I pulled it off the board and it registers 0nF)

 

Based on the schematic the line is Pin 31 (PWR4069) from the ROM cart. I do have the cart in while testing. I do have continuity from Pin 31 to C52.

 

I'm going to replace C52 before doing any more testing and report back.

[ThatGuyUKnow]

In the process of replacing it I looked again at the schematic and for the purposes of continuity it shouldn't matter whether C52 is good or bad since it shows there should be a direct connection between Pin31 of the rom cart and the ground for the power rail which in this case I'm measuring from C35. If I'm reading the schematic correctly, I think the trace between C52 and C35 is not connected and I should run a wire. Do you concur on this assessment? I included the area of the schematic for quick reference.

[ThatGuyUKnow]

Here is the lower part of the schematic. I forgot to upload this earlier.

[+Stephen Moss]

16 hours ago, ThatGuyUKnow said:

In the process of replacing it I looked again at the schematic and for the purposes of continuity it shouldn't matter whether C52 is good or bad

C52 being bad could make a big difference if it is shorted as positive power would then be connected to the single point GND and there would be no voltage drop over 90% of the circuitry with its GND and VCC being the same voltage, plus if it did ever turn on Q12 &/or L15 would probably burn out as the power supply would essentially be shorted out through them.

17 hours ago, ThatGuyUKnow said:

no continuity to C52 (I can't pass voltage in diode mode, I pulled it off the board and it registers 0nF)

You cannot pass DC voltage through a capacitor unless it has gone short circuit (capacitors are open circuit to DC, pass AC). I would not use Diode mode for continuity checking, most meters have a mode for that with an annoying buzzer which can go off at a resistance less than 50R so not necessarily a 0R continuity, thus always read the displayed resistance rather than rely on the buzzer alone which I personally can't stand and prefer to use the 10K resistance range. 

That aside reading 0nF when is should be 100nF would initially suggests a possible short, did you measure its resistance to see if it was a short circuit? 

16 hours ago, ThatGuyUKnow said:

since it shows there should be a direct connection between Pin31 of the rom cart and the ground for the power rail which in this case I'm measuring from C35.

I am not sure if it is your thinking or your description that is wrong here. Did you mean...

a) That the continuity check has reviled that there is a short across the supply?

b) That there is no continuity between the GND connection of C52 and C35 - which would be correct, there is no direct connection between the power GND and the Single Point GND.

If not either of those I do not know why you would appear to be thinking that there should be a direct connection between the supply voltage for U6 and GND as that would be a short across the supply?

16 hours ago, ThatGuyUKnow said:

I think the trace between C52 and C35 is not connected and I should run a wire. Do you concur on this assessment? I included the area of the schematic for quick reference.

DO NOT run a wire if that means you will be creating a short across the power supply or the Power and Single point GNDs (re comment above).

 

I cannot check on my Lynx as it is at work and I am on furlough but if you meant the Positive power rail connection between Pin31 of the ROM Cartridge/positive side of C52 and the positive side of C35 rather than the GND side of C35 I believe that the positive supply connection runs from the positive rail side of C35 via L10 to pin 33 of the ROM cart, via the ROM Cart to Pin31 of the ROM Cart, and then to C52.

 

In you GND continuity check you did not indicate the condition of the connection to Pin 7 of U6, please try to establish is there is continuity from the Battery Connector to the respective power pins of U6, if that checks out then try to measure the supply voltage to U6 with your meter probes on pin 7 & 14 to verify its supply voltage, if possible with both a power brick and batteries as the voltage source.

[ThatGuyUKnow]

On 6/29/2021 at 3:57 AM, Stephen Moss said:

DO NOT run a wire if that means you will be creating a short across the power supply or the Power and Single point GNDs (re comment above).

I misread the schematic. I haven't finished my EE degree and the way I read the schematic it looked like they were tied in because I over looked the op amp in u6 that the line clearly went into. *facepalm*I haven't done anything yet which is obviously good.

 

On 6/29/2021 at 3:57 AM, Stephen Moss said:

In you GND continuity check you did not indicate the condition of the connection to Pin 7 of U6, please try to establish is there is continuity from the Battery Connector to the respective power pins of U6, if that checks out then try to measure the supply voltage to U6 with your meter probes on pin 7 & 14 to verify its supply voltage, if possible with both a power brick and batteries as the voltage source.

  Pin 7 of U6 has continuity to the ground rail. I tested continuity to both C42 and R71.

 

Battery positive continuity to C36, From C36 to the base of Q7, through the transistor, collector continuity to TP18 and pin 13 of U6.

 

Using the wall adapter, with the negative lead on pin 7 and the positive on pin 14 it starts around 4.5v and then rapidly falls to a low mV rating. 

 

Using batteries the power comes in pin 13 via Q7 the transistor has 9v on the base, 8.3V on the emitter and 45mV on the collector going into pin 13. The emitter leg is noted on the silkscreen and the data sheet shows the single pin as the collector. If I measure negative on pin 7 and positive on pin 14 it reacts the same way as with the wall adapter starting around 4.5v and rapidly falling down to a near 0 reading.    

 

Using the wall adapter I get 8.43V on the emitter of Q7 and 45mV on the collector. 

 

What I am questioning is, are the transistor readings correct? 

[ThatGuyUKnow]

I wanted to give an update in case anyone runs into a similar issue. I was doing research in the forum and found some posts by RJ1307 who gave information on using jumpers to bypass the flex and the cartridge to rule them in or out as issues.

 

I did this and the system worked. I disconnected the one for the flex. It still worked. I disconnected the jumper for the cartridge (pins 31 and 33) and it no longer powered on even with a game installed. I cleaned the slot with 99% IPA and a nylon brush. I then used flux to Re-flow the pins for the cartridge slot. This fixed the issue.

 

It’s obviously coincidental that I had done some work to the board as this issue was unrelated.

 

This jumper method is a great starting point for any power related issues with the Lynx ii so you can determine if it’s a flex, cartridge, or power rail issue.