Need help, my repair of Lynx2 power circuit does not work as expected...

[Sporny Kun]

Hello,

 

I have a Lynx 2 with what seems dead power mosfet (Q12) : black screen on power up, 8~9V on C41.

 

In short, after replacing the mosfet and the zener diode, I still have ~7.7 V on C41 instead of 5V, with around 4.5V at the zener diode, and 3.3V between TP18 and TP19.

 

The complete story :

I finally ordered a mosfet and a zener diode. There is a thread there listing a suitable replacement by @karri and all, but I cannot find it again. Anyway not available at mouser, I tried to chose another one with those parameter :

 

Quote

Mosfet : SMD/SMT TO-252-3 N-Channel 1 Channel 100 mOhms 60 V MOSFET

(active ref : STD12NF06T4)

I(D) = 12A Drain or more,
P(TOT) = 30W dissipation or more,
V(GS) = 2V Gate threshold.

I selected this one : https://www.mouser.fr/ProductDetail/844-IRFR020TRPBF  (IRFR020TRPBF  from Vishay)

 

For the Zener diode, I searched with those parameters :

 

Quote

4.3 V SMD/SMT 5 mA Single 5 mA 90 Ohms Diodes Zener

Package : probably SOD 123 (typ 3.55—3.85mm) ?
else SOD 323 (2.3—2.7 mm) ?

I selected this one : https://www.mouser.fr/ProductDetail/621-BZT52C4V3-F (BZT52C4V3-7-F from Diodes incorporated)

 

So, my first question : did I chose correctly ?

 

If yes, are there other components to replace in this case to finaly get 5V ? Or other thing to checks ?

 

For now I do not expect the Lynx to work, but at least I would like to repair this part.

 

Regards

[+-^CrossBow^-]

Did you also replace the two small transistors as well? Search around these forums, as there is quite a bit to find and help your troubleshoot such as checking various voltages from U6 etc to try and help isolate where the issue lies.

 

I will state that having a +5 only PSU of about 1A that you can wire up directly to C41 will help to know if the Lynx is at least able to work or not. If you have a cart inserted and have +5 going directly to that cap to bypass the power stage, then the Lynx will power on and hopefully display the game to be played.

 

[Sporny Kun]

Thanks for your answers.

 

I already tested with +5V feeded directly at C41, black screen too. I will try recapping after I have fixed the power circuit.

[+karri]

Console 5 sells small power upgrade kits. I have used them lately instead of hunting for the components from the big houses.

 

The kit also includes the power connector that is very often broken as well.

[Sporny Kun]

Thanks, I will look at that later.

[battleman13]

On 8/13/2021 at 11:15 AM, Sporny Kun said:

Thanks for your answers.

 

I already tested with +5V feeded directly at C41, black screen too. I will try recapping after I have fixed the power circuit.

If you pumped 5V 1A directly into the legs of C41 (and had polarity correct) you should have had a game running. I like to do this with a game like chips challenge, that plays sound almost right away. Lets you know if the game is "playing blind" so to speak. Meaning the game is running, sound coming out of the speaker (which keys you in to the game running) but nothing on the display. Lets you know at least "most things" are working OK. 

If you are not getting sound or video, with 5V going in to C41 then you likely have damaged one of the two custom Lynx CPU's or the two ram chips.

[Sporny Kun]

3 hours ago, battleman13 said:

If you are not getting sound or video, with 5V going in to C41 then you likely have damaged one of the two custom Lynx CPU's or the two ram chips.

Yes, that is my guess. I have another Lynx 2 that is still not fried (it was sold with the "headphone hack" to bypass the power circuit, fortunately still running), so I am using the probably dead Lynx as a training.

[+Stephen Moss]

On 8/13/2021 at 2:25 PM, Sporny Kun said:

In short, after replacing the mosfet and the zener diode, I still have ~7.7 V on C41 instead of 5V, with around 4.5V at the zener diode, and 3.3V between TP18 and TP19.

When you say 7.7V on C41 was that measured directly across it or just at one end?

Why measure the voltage across TP18 and TP19? I fail to see how that would be of any relevance.

On 8/13/2021 at 2:25 PM, Sporny Kun said:

I have a Lynx 2 with what seems dead power mosfet (Q12) : black screen on power up, 8~9V on C41.

Same question as above regarding C41 voltage and did the Lynx power up as soon as a power source was connected 

 

[Sporny Kun]

hello @Stephen Moss, Voltage on C41 was measured directly accross C41.

 

Feeding 5V directly to C41, the lynx power up immediately.

[Sporny Kun]

Hello, a little follow-up, to say that it is solved.

 

I ordered and received a kit from console5. I replaced the 2 transistor (q7 and q8).

 

 

Now the voltage at C41 is right. (this console is still fried elsewhere, but it was a training before working on the other one that I know is still not dead)

[Sporny Kun]

Small epilog, I installed the same kit on my second lynx.

 

On this one, the transistor Q8 was burnt. That's why the previous owner modded the console to bypass the voltage regulation. (I have since removed this mod as I know that it was steadily killing the console.)

 

And this led to a tragic pad lift when I removed it...

 

I was fortunate enough to find where the remaining track went (with a bit of checking against the schematics), and I wired the dangling pin to an easy to solder location, at U6.

 

This lynx is saved !