Turbo Express with no 5v

[Dr Honda]

Hi Guys,

Since COVID, I've been working on some system for the local used game store, and I have a problemed TE on the bench.  The story with it is.... it was already recaped, and it worked for months. Then, all the sudden, the sound got strange, and the screen went black.

First thing I did was simply put fresh batteries in it, and verify the HuCard would work in another system.  I also put it on a power supply.

As I picked around the board... I checked the fuse (it's good) and cleaned up a few caps that looked questionable.  I also looked for shorts across caps. (most of the replacement caps are surface mount)  So... while it's not great work... all the caps are OK.

After reading a few things here... I checked for 5v... and sure enough... NOTHING.   I can follow the supply voltage to the B1182... but nothing out.  On Console5 it says it's a "Simple Zener adjustable regulator"... and on a thread here there is a comment saying to "Check the regulator".   But... what IC is the actual regulator for the 5v side?  (I'm assuming the B1182 is for the back light) This would be so much easier with a schematic, because the mask on this thing is crazy thick. LOL.

Oh... last thing.  Since there was a comment about "There should be 5v on almost every cap"... and I could see what caps were on the 5v buss on the TG16 schematic... I fed 5v directly to a cap that I verified was on the buss... and I got sound from the game.  (So the chipset is OK)   But no picture.

Anyway... any guidance with this would be very appreciated.

****EDIT*****

I just wanted to add... when I put power on the board... nothing gets warm, and I cant find anything that looks burnt.

[MasterofBiscuits]

B1182 is the DC-DC regulator and you should have 5v on the collector, this is controlled with VR501 and ZD501 is the zener diode. Try injecting 5v to the large pad and see if you get any life. Perhaps one of those components has failed (probably the zener).

The backlight is powered via a transformer which sits under the large cubic shield.

[Dr Honda]

Thanks for the info !!!  Once I get down into my shop... I will put power on the C of the b1182.     I will also lift ZD501 off the board to check it.

Thanks again.

[Dr Honda]

Ok...  I put 5v on the big tab of the B1182, and I get nothing. So, I lifted it off the board, and I still get nothing with 5v soldered to the pad on the board.  For giggles, I lifted ZD501 off the board, and it seems to be OK.   I get 0.6xx V, and 2.8xx V in diode mode.  And I get a few Meg Ohms one direction, and OL the other.   Just for verification... I checked a new Zener I have for an Atari Lynx (also 6 AA batteries, and needs 5v)  It gives me more or less the same readings.

Since that didn't bring happiness... I decided to check all the caps for a short.  I found that C900 is shorted. (small ceramic)  So I took it off the board, and it was ok.  The 2 pads show continuity.  But, it looks like it's connected to the transformer for the backlight.   Incidentally, I do have a backlight. (Just a black screen)

So, anyone have any other thoughts?

Thanks


****EDIT*****

From the pad of the B1182 to any of the 5v pins on the chips, and Caps, I have 4K ohms.  Seems like a lot of resistance if that's the output for the 5v side of things.  And, it seems strange since there isn't anything between the regulator and those pins on the TG16.  Does anyone have a schematic for this thing?

[MasterofBiscuits]

You say you have a backlight and no picture, can you describe how the screen looks? Does it have a greenish tinge like this?

[Dr Honda]

@masterofbiscuits

yep, just like that with either batteries, or power supply.  Back light on... pixels are dark.    And, if I put 5v on a cap tied to the chips... game boots with sound... but still no pic.  5v on the tab of B1182 gives nothing.

[MasterofBiscuits]

If it looks like that, the backlight is not on. This is what it looks like when the backlight is not working - I had exactly this problem myself and thought the same thing. But actually that glow from the screen is the LCD itself.

It sounds like there may have been a failure on the backlight circuit somewhere. Personally I would remove, clean pads and replace all the capacitors just to be certain that those are not the problem. If no change, replace Q900 and Q901 as these can sometimes fail and are used for the backlight.

I never actually managed to fix mine, though I did get it working by putting in a 3.5" LCD mod.

[Dr Honda]

@masterofbiscuits

Thanks for the info.  I guess I made the assumption that the glow was from the backlight. (I've spent too much time working on old Nintendo handhelds)

Interesting on the screen mod.  The person who gave it to me to look at was asking about doing the screen mod, but I told him that I want to get it up and running before the money was spent to do the mod.   So, when you disconnected the screen from the system... did the 5v come back to the rest of the board? I guess I should open that solder jumper to "Turn off" the backlight and see what I get.  Or... was there something else I should look at to remove the backlight power?

Again... thanks a bunch.

[MasterofBiscuits]

Mine was a little different as I did still have sound when the backlight wasn't working, so I think you are right to try and get that working before doing the mod. Removing the BLH solder jumper is definitely worth a try, just in case there is something in that circuit shorting the whole thing out.

I would also try recapping it, just to rule it out as the problem. Unfortunately there is no schematic for this as far as I know which makes fixing things such as this very difficult!

[Dr Honda]

Thanks again.

I pulled Q900 and Q901 off the board, and they check fine.   BUT... I found that R512?  (maybe R517 have to go back down to the shop) is showing a short.  I lifted it off the board and it's showing 33 ohms and the pads are shorted  SO... I'm guessing that there is a transistor somewhere burnt up.

Also... I'm getting voltage on the pin going to the battery when there is a supply plugged in.  I would think there is a diode that would block that.  SO... since that resistor is showing a short... I'm guessing there is an issue in that section of the board.

Any other thoughts or input would be appreciated.

[MasterofBiscuits]

Another transistor to check is Q500 in the top corner - this is also part of the backlight circuit and has been known to blow and cause backlight failure. Not sure what else to suggest 

Oh by the way, I found the best way of looking at the traces was to shine a light through the back of the board, it really helps when you're trying to follow them. It's also easy to see which are front and which are on the back.

[Dr Honda]

Thanks for all the input so far.

I was kind of suspecting Q500 and the diode close to it on the back side. (under the gray stuff)  That's where I found the resistor showing a short.  But, before I got a chance to take it off the board... I had to step away from it.  LOL.  If this was my person unit... I would sit and lift ever single part off the board until I found it.  But this is for someone else... and it has someone else's prior work... and it just makes it that much harder to want to sit with it.

Do we know the replacement for Q500?   Q900 and Q901 I found at console5.

[MasterofBiscuits]

Q500: https://www.aliexpress.com/item/32726193004.html

I know what you mean, there is a point where it's just not worth the time. Always good to take a break anyway, sometimes having fresh eyes on it makes all the difference.

[Dr Honda]

OK... lifted Q500 off the board, and it checks ok with a meter in diode mode.  BUT... I got that nasty fish smell when I heated it up.  It was good to clean under it at least.

The light trick was a big help.  I cant see everything... but things started to align in my head.  I could now see what groups of parts, and though holes I needed to look at.  AND, it shed some light on R517. It shows a short because it's on both legs of one of the small coils. 

On the power input side... under the gray stuff is D500.  Do we know what that is? (Kind of diode)  I can see a diode on one leg... but not the other. (in either direction) I'm starting to suspect that is keeping power from my 5v side. (The traces are all hard to see there)

And in the 5v power section... I have 2 questions...

1) Do we know what Q503 is?   I can see the Zener, and the input power are on it. (bottom 3 legs) but the top 2 legs don't seem to be connected internal. (Checked it in diode mode)

2) I get continuity on the tab of the B1182 to TP501.  BUT, to any of the "5v Buss".... I'm showing 4K resistance.   Is this what you get on a good running Turbo Express?  It doesn't make sense, since the TG16 is clean from the regulator to the 5v side of the chipset.

Again... thanks for all the input.

Oh... and if this was a gameboy, or 3DS... I would have told the customer it's not worth the time to do board level repairs.  But these things have gotten crazy expensive... and now it's personal.  LOL.  No mater how much time I put into it... I'll probably only charge the guy $40.  I see this as a good learning experience. Besides... the owner isn't in a rush.  He has another one.

[MasterofBiscuits]

I'm guessing that leaking electrolyte has shorted something out, which is exactly what happened to mine. Every GT I recap now gets a good scrub with IPA and then PCB cleaner sprayed all over it.

Afraid I have no idea what Q503 is or does. I have a stock GT here that I am about to work on, if you want me to test some points with a multimeter let me know and I will go over them when I have it cracked open.