Possible Dead Lynx 2

[Dresden]

Hey folks,

 

I bought a used Lynx 2 with issues in hope that I could repair it to working order. I was making good progress. I did a full recap, and did the power circuit with the kits available from Console5.com. I did accidentally remove C36, which then proceeded to fly across my workspace into the nether. I did replace it with another .01 uf capacitor, but the issue I was having existed before I did that. 

 

When I power it, I get a black screen, the initialization of the speakers, but no image. I also noticed the smaller of the two main chips will eventually heat up quite quickly. This is via AC or the USB hack.

 

It was working after the recap, and before I replaced the power components. I was able to power it on linking a USB cable to that first big capacitor, but I couldn't get a response on battery or AC, which lead me to believe that something was wrong with the power components and after I replaced those, minus my C36 incident, I figured I'd be in the clear.

 

Can anyone recommend a course of action to test and try from here? Maybe I fried one of the new components? I did replace the AC connector initially too, but it was too tight and the core of that connector eventually came out with the adapter and I swapped the old one back in. 

 

I have another Lynx 2 and kits on the way for a second attempt since I've already ordered a BennVenn screen. I have an original Lynx 1, but it was my childhood unit and still works fine. I'd love to get a 2 working, especially with the fancy new LCD.

 

If anyone has any advice, I'd greatly appreciate it!

 

-Bill

 

[Dresden]

Anyone? Help? Ideas? 

[+Stephen Moss]

If by USB hack you mean attaching a 5V source to either C40, C41, C44 or R75 then I would be the first thing that come to mind is whether or not you connected the power the correct way round as you may have damaged something if you had the polarity reversed.

 

I have never tested the Lynx IC to see how quickly that heat up and to what temperature but anything heating up quickly is not a good sign and usually means it is damaged or too much power is being applied.

Double check you work on replacing the power components, I am not sure which component you replaced but if it involves the Zenner it is very important that you install it the correct way around, also check for solder shorting out to place it should not.

If you are not sure if the Zenner is in the correct way around they check the first paragraph of this post for a quick method of checking, but only switch on for the shorted time possible as the longer a device is overheating the more damage is done.

 

Alterative (or if the Zenner voltage measured does not seem correct) I would suggest you remove the power supply components you installed and connect a 5V source to either C40, C41, C44 or R75 (observing the correct polarity) and see if the black screen and overheating problem persists. 

[Dresden]

Thank you Stephen! I will try that tonight. I appreciate your time.

[Dresden]

Ok, update. I took off the Zenner and checked everything and then soldered on the USB power to C41 (the big cap) and it still turns on, black screen, no overheating because 5V, but also it powers up with or without a cartridge in it, which I thought wasn't supposed to happen if there was no cartridge, so that leads me to believe there might be a short somewhere then? I didn't connect the two cartridge pins or anything. Thoughts?

[+Stephen Moss]

If I have understood your reply correctly you were powering the Lynx from a 5V USB supply connected to C41 with the Zenner removed and no cartridge connected, if that is the case then the fact that things are not overheating with a 5V supply is an improvement and it suggests to me that the overheating may have had more to do with an an overvoltage issue rather than a fundamental issue like an internal short on the device. If that is indeed the case then the mostly likely causes of overvoltage are...

 

1) That somebody have employed that horrid Speaker Ground hack linking the 5V "GND" to the main supply ground to bypass a problem with the power stage rather than attempt a proper repair.

First look to see if someone has use the speaker ground hack, if they have the remove it (probably a wire from the speaker connector to the battery connector/power socket/D10/D11/C35) or possibly across two pins of Q12.

2) A short Circuit of Q12 (if you have a DMM set it to the 2K resistance range and measure across the top left and bottom pins (try with leads both ways round), an over range reading means no short. 

3) Inserting the Zenner the wrong way around may cause it (not 100% on that) as the voltage drop would only be 0.7V not 4.3V.

If the Lynx power on as soon as a power source was applied that is generally a good indicator of options one or two. 

 

If the speaker GND hack was used they may have also wired in the cartridge bypass linking (as I recall) pins 31 & 33 of the cartridge port so check for the presence of that. However, for now the reason it is powering on without a cartridge inserted at this stage is due to you running the Lynx off the USB supply connected to C41 as doing so bypasses the whole power circuitry section of which the cartridge pass though is a part. 

 

Does the Lynx appear to be operating correctly when powered from the 5V USB supply with a cartridge inserted or are you still getting a blank screen?

[Dresden]

1.) No, the machine was untouched when I opened it, so no other hacks deployed, and that's not one I even tried to do.

2.) I will check that tonight. 

 

The cartridge pins aren't bpyassed either, and ok, I didn't realize it bypassed even the cartridge connection circuitry, so that explains that.

 

It is still blank and not working though, which leads me to believe I probably fried something.

 

[Dresden]

I got a bench top power supply today to make it easier and more reliable than futzing with a USB cable. Still nothing at a pure 5V into it. I did not get any resistance reading on the MOSFET (Q12) at all, but even in bypassing it at a perfect 5V, I'm pretty convinced I fried the damn thing. 

[+Stephen Moss]

You could be correct in that the device that was getting hot is damaged and that is preventing the Lynx from working correctly but that may be a few things you can check.

When you say you did not get any resistance reading for Q12 did you mean it read 0 (short) or over range (1 on left of display) in which case it may be OK?

 

If you look at the post here you will see some resistance measurements I made on my Lynx 2 with no power source connected and no cartridge inserted. They largely refer to the power stage but a fault there may be what caused the overheating as it is not occurring when powered from a 5V supply so you might want see how those measurements on your Lynx compare.

 

If you make those checks and you get similar reading then with a cartridge inserted and your 5V supply attached locate component R1, D1 and C3, and/or TP1 (top left corner of the schematic, probably under the shield). These are the reset circuit component, a fault there could be keeping Hayato and Suzy in reset. Place the com leads of you meter to the connection point of your 5V GND and the V/Ohm lead to either TP1 or the intersection of R1, D1 & C3, you should get a reading of about 5V DC.

 

Do watch out for the high voltage transformer T1, it create 2000V DC for the LCD backlight and is right where your finger go when using the Lynx, touching it will give you a nasty nip.  

[Dresden]

I believe it was a 0. It was a new MOSFET, and I have another set (I ordered an extra set with the stuff for the second Lynx I just got.) In reading around, it appears they're sensitive and I possibly killed the new MOSFET. I'll check those out later tonight or tomorrow, thanks again for your help. I hope I get one of these working 100%. 

[Dresden]

Ok, sorry for the delay. It's been a week. I had to get a new multimeter too, because my old one I used for mostly automotive/motorcycle purposes and had gas splashed on the screen which made it blurry. Good for reading a 12V system, but not much else. 

 

So in reading the MOSFET, if I put the red on the upper left, and the black on the bottom, I get a reading of about 490 ohms. (Set to 2k)

 

I got my second Lynx, which is a lot like my first Lynx, i.e., not working. 

 

In testing to TP1, I get about 4.9 volts. I have the power supply set at 5V 1 AMP, powering through the big cap in the top left.

 

If I have it hooked up to the power supply, and I've removed the diode, does that matter? Dumb question, but I was under the assumption that only mattered in powering from battery/DC jack, not from C41. 

 

So I've got two Lynxes now that are doing the same thing, aka nothing.

 

I recapped the second one, but I haven't messed with anything else. I haven't taken the shield off yet either.

 

Hoping to get one of these going before my BennVenn screen arrives.

 

Thanks again for your advice.

 

[+Stephen Moss]

Well it looks like the Reset is being pulled high, if you can confirm that 5V is appearing on the resets pins of U1 (Hayato, pin 57, 4th up on left side) and U2 (Suzy, pin 4, bottom edge 3rd from right), although if if that checks out we can only they are not being held in reset due to an internal fault.

 

You should not need the Zenner in if powering it correctly from a 5V source.

 

Your previous reading of 0 for the Q12 MOSFET and you latest reading of 480R seem a little off when compared to what I would expect and the readings I posted, assuming it is the original MTD3055E device. But then I did not have an external power source connected and the Zenner removed. Unfortunately, I do not currently have access to my Lynx to triple check my measurements, just in case I made an error. But that is a secondary concern related to a possible power supply fault that caused the overheating so probably not get too involved with that just now. 

 

You could try measuring the voltage across the pins (one meter lead on each pin) of the crystal (grey rectangular with 16.000 written on it) or R10 to try and ascertain if the oscillator is running.

 

If the original LCD screen is still fitted the backlight is a bulb that runs across the width of the screen with a metal cap at each end, there should be enough of the tube visible for you to see if that is on? If it is not on there will be no screen illumination.

If it is not on at power up (with both the LCD and button flex circuits inserted into their connectors and the backlight power connector plugged in) does operating the Backlight button switch it on? 

If the backlight was not originally on and you can turn it on with the backlight switch are you getting anything displayed? 

 

[battleman13]

If your applying 5V (stable... and not high amps... 1 amp would probably be enough) directly into the legs of C41 and the machine is not "working" there are two likely culprits.

1) The cart slot and or the cartridge are dirty. A hacky way to check that is to remove and insert the card, with a wee bit of force, about 10 or 15 times. Then test the machine. Cart slots can also have bent, corroded or burned up pins.

2) One or both of the custom CPU's got damaged by over volting when you applied AC / Battery power. Those are 9V power sources that get regulated down to 5V by the power circuit. When components in that circuit fail (and the original parts are often failed by now) they can fail one of two ways. Closed, or open. In one case, the unit simply won't power up. In the other case, 9V is fed into parts that should only get 5V. If it's the 9V into 5V case... those custom CPU chips or the ram chips can be destroyed... essentially making that lynx junk. Unless you want to order proper replacements from Best Electronics in California and have the hot air station and skills to replace those quad flat pack chips.

In a healthy lynx 2 (meaning the critical, nearly non replaceable parts are OK) applying 5V to C41 and having a game in the cart slot will have the system auto start and the game load. This bypasses anything beyond the ram chips and the custom CPU's. The only factor here, beyond that, would be a faulty screen, bad power caps, bad or dirty cartridge, or a bad or dirty cartridge slot.

[Dresden]

Is there any definitive way to see if it's one chip or the other? I know the smaller one, the Suzy is readily available on AliExpress, and that's the one I think I killed in the first one. 

 

If there's a good way to test, maybe I can make one good one between the two. I have a hot air setup and I've done that before. It sucks, but it's not impossible.

 

Thanks Stephen and battleman for continuing to guide me.

[Dresden]

I gave up for now and bought a third Lynx that's supposedly working. 

 

I'll monkey with these later and maybe between the two I can get one working one. I'd still like to know if there was a way I could test the chips to find out which one is toasted. Ideally, I could just swap one from the other if it's different. 

 

My BennVenn screen came and I just want to play Rampart.