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NEC TG-16/TE/TurboDuo => TG/PCE Repair/Mod Discussion => Topic started by: schweaty on May 07, 2014, 12:31:19 AM
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Gents,
I have reached the limits of my knowledge so I need a little help.
Background: I am doing a repair for someone else. It did not have any sound or pic, but according to the pics he sent, it did power on and the screen turned white at highest brightness setting. When I got it, the battery compartment was corroded and the negative power lead was so corroded it just fell off the post during disassembly (i'm shocked this thing ever powered on). I replaced the blue power lead and all the capacitors.
Current State: TE powers on with backlight on the screen and nice loud sound, but no pic at all. The brightness adjustment also doesnt change the pic at all. Correct me if i'm wrong, but I believe even when the CC501 cap is bad you still get brightness adjustment if the backlight comes on (assuming no other faults). So, I have a TE with sound, but a black backlit screen.
While replacing the capacitors, 2 pads lifted. The 1st pic below is the CC700 cap. Its kind of hard to tell in the pic, the the pad is indeed lifted. I soldered the negative end to a hole near the pad after scraping back to the copper. There were 2 holes near the pad and I have tried both with no change to the current state. The second 2 pics show the pad clearly lifted from CC501 (video cap). The negative pad also lifted and it is currently soldered to the TestPoint described by Charlie to fix a lifted negative pad. I also tried soldering it to the hole just below the '0' in "501" and i scraped back to the copper of the lead going to the chip with "BA" on it (cant remember what it is called right now) that Duo-R described in his post (pink oval). That also had no effect on the current state. As you can tell, I've gone thru all the fixes described in the cap replacement thread for a lifted CC501 negative pad
I have also swapped the screen with one that I know works and still get the same result. I'm all out of ideas. Any help is appreciated
-Dan
(http://i.imgur.com/g7lCAbUc81e.jpg?2)
(http://i.imgur.com/313mSYmc4ca.jpg?1)
(http://i.imgur.com/eQ5GIZ5c81e.jpg?2)
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Negative end in this pics goes here
http://postimg.org/image/w7iel4c99/ Here.
I'll double check your other one when I get home from work and update.
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Negative end in this pics goes here
http://postimg.org/image/w7iel4c99/ Here.
I'll double check your other one when I get home from work and update.
Forgot to mention in OP. I tried that one too. no dice
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I ran into this a couple of times before. It has something to do to the power to the LCD. Check the voltage of the blue capacitors? It should also have something to do with the transformer also. I get around this by doing the LCD mod.
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I ran into this a couple of times before. It has something to do to the power to the LCD. Check the voltage of the blue capacitors? It should also have something to do with the transformer also. I get around this by doing the LCD mod.
EDIT: withdrawn in shame
-Dan
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I'm sure it's fixable but thesteve would have to chime in.
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i withdraw my last post. i rechecked the caps (this time on the proper setting). I am actually getting 24V on the 22uF35V, 24.5V on the 4.7uF35V and only 30V on the 4.7uF50V.
I found theSteve's old post about the low-voltage issue. I may have to adjust the pots to get more juice flowing, but it will have to be later tonight. I will keep you informed.
theSteve can chime in any time... always welcome
-Dan
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Well back to square one. I checked the voltages of the same caps on my good TE and I got the exact same readings. I'm truly stumped now. Completely out of ideas.
Any help is appreciated
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"So, I have a TE with sound, but a black backlit screen."
Is it totally black? or is the backlight still white as stated first?
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"So, I have a TE with sound, but a black backlit screen."
Is it totally black? or is the backlight still white as stated first?
it is totally black. i can tell its on, but it does not turn white at all like when you first turn on a normally functioning TE. and brightness adjustment has no effect at all.
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That could be progress, take a shmup or a game with lots of movement, take out the brightest flashlight you can find, point it at the screen, and at different angles, do you see any movement lurking back there? if so it should be an easy fix.
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That could be progress, take a shmup or a game with lots of movement, take out the brightest flashlight you can find, point it at the screen, and at different angles, do you see any movement lurking back there? if so it should be an easy fix.
I don't see anything when I try that
Just to clarify what the screen looks like, when viewed from an extreme upper or lower angle, it is white. I have swapped the motherboard out with my good TE, and it worked. The problem is somewhere on the motherboard
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Usually it's Q900, Q901, they go to each side of the cold light, like one positive and on for the negative, the excessive white when started could come from that only one is working.
dial wheel function does not work when they are not working as they should.
the extreme angle for that little light could also be that only one is working.
Usually there is a murky picture moving around since the video and the backlight are to very separate things, they do their own thing and it's less likely both would go out, they don't share much circuitry and if both are out it would mean you have two faults and not just one.
And it's usually really hard to see, the screen has to be outside the shell for the light trick, the best way to really rule it out is to shine thew it.
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Usually it's Q900, Q901, they go to each side of the cold light, like one positive and on for the negative, the excessive white when started could come from that only one is working.
dial wheel function does not work when they are not working as they should.
the extreme angle for that little light could also be that only one is working.
Usually there is a murky picture moving around since the video and the backlight are to very separate things, they do their own thing and it's less likely both would go out, they don't share much circuitry and if both are out it would mean you have two faults and not just one.
And it's usually really hard to see, the screen has to be outside the shell for the light trick, the best way to really rule it out is to shine thew it.
i took the screen out of the case and tried it with the light, but there is nothing there. i literally had my face right up to it with a LED flashlight and i am fairly certain if there was anything to see, i would have seen it.
i feel like i may have confused some people with my description of what is going on with the screen. the backlight absolutely IS on. there is just nothing on the screen. it is blank when i know the game is running (the sound works perfectly). while its on, if i tilt it all the way up or down, the screen looks white
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Then you have two faults to look for, one for video and one for backlight, they are separate problem in themselves but electrolyte from a one or several capacitors could have corroded vias that they have in common.
Do what you just did but take the red cable out completely, that would disable the backlight temporarily, it might be easier to troubleshoot the video problem then, the dysfunctional extreme backlight settings can cloud the visual view of the video.
Doing the opposite can also be done for fiddling with the backlight but not as necessary.
Something weird happened to me a couple months ago, my GT I'm using for the GT/TE component guide started to show darker picture, the brightness usually goes up as battery voltage goes down (does any other handheld show more brightness when voltage is dropping? not what I'v seen)
anyhow, I read newly somewhere that CC500,900 would show a decrease in brightness if they were going bad, they're pretty newly replaced, tantalum, checked them and they were good, tested the unit without them, and surprisingly worked just as fine... soldered them back and realised that the minus side of the red connector had come loose on the connector that goes into J500, resoldering that made the brightness become normal again.
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they may not be separate
the controller board switches 5V to the screen and switches the backlight supply
check your voltages at the screen connector(posted the pinout some time ago, looking for it now)
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http://www.pcenginefx.com/forums/index.php?topic=4869.msg186903#msg186903
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they may not be separate
the controller board switches 5V to the screen and switches the backlight supply
check your voltages at the screen connector(posted the pinout some time ago, looking for it now)
OK Steve, here's what i have:
1: 0.0V (of course)
2: 1.9V
3: -24.0V (bang on)
4: 0.4V
5: 3.2V
6: 3.1V
7: 3.3V
8: 5.0V (the first reading was 4.7V but I adjusted the pot to bring it up to 5.0V)
If I can't get this fixed in the next couple of days, I might have to send it back to its owner. I've already spent 4 days working on it without any change. It wouldnt be fair to me or the owner to keep it much longer.
Thanks again for all the help so far.
-Dan
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Those numbers look ok except possibly pin4
Can you check with scope, or compare to good one?
Also check your 5v at the 470uf cap for adjustment
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Those numbers look ok except possibly pin4
Can you check with scope, or compare to good one?
Also check your 5v at the 470uf cap for adjustment
so i just checked my good TE voltages using the same game and same ac adaptor. here's what I got:
1: 0.0V (duh, dan)
2: 3.53V
3: -24V (again... bang on)
4: 0.4V (same as the bad one)
5: 2.9V
6: 2.84V
7: 2.77V
8: 4.8V
so what jumped out at me was pin 2 (brightness) was nearly twice as high as the non-working TE. Also my RGB pins are all about .5V less than the non-working TE. that seems like a lot of variance for such low voltages.
what did you mean by check 5V at 470uF cap for adjustment? is there a pot around there I'm not seeing or just check the voltage at the cap for at least 5V?
-Dan
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the screen 5V should be a bit low, so when you adjust it put meter on a non switched point
card slot, regulator, always live cap ect
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also your pin2 is controlled by the brightness pot
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i adjusted the 5V pin down to 4.8V. Which one is the brightness pot? As far as I can tell, the VR501 pot adjusts the 5V pin and the VR501 adjusts the 24V pin. Neither had an effect on the brightness pin that i could see
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user brightness
by the vol pot
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another, duh-dan, moment for me. i never really thought of the brightness wheel as a pot, but that is exactly what it is.
no matter what that is set to (highest or lowest), pin2 only reads 1.8V. I'm assuming its supposed to go up and down as the bright wheel is adjusted.
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Correct
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so, do you think this is the root cause of the problem (no picture on screen)? if so, what can i do to fix it?
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It is the likely cause
Confirm the screen works on another board and trace pin2 voltage
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I just fixed a TE with this exact same symptom. Turns out that one of the caps on the board that I had changed had a bad trace going to one of the positive ends. Did you double check that all the caps have a voltage of some sort on their positive ends? The one that was causing my issue had no voltage at all. I just double checked each one until I found the culprit.
Not sure if this was already covered in the postings here because I just skimmed them quickly. Just thought I'd mention what I had to do for a TE I had in case anything was overlooked.
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well put KC
thats why i say to check the voltages on the caps
note that sometimes the voltage will be on the negative, so check across the cap, not to ground
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thanks, guys. i will check all the voltages again. the first time i checked, I think I used a common ground for the neg lead.
the screen was checked on a good TE and it worked perfectly, so now its just a matter of finding the gremlin.
If any of you guys could give me a path on the pcb to trace from pin2 that you are aware of, i would also appreciate it.
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that board can be a pain to trace as its a bizarre multilayer board
the board is double sided, than insulation painted, than another copper layer on top of that.
if i had one apart i would trace it, but ATM i dont
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just rechecked every cap. everything seems normal except the 10uF16V. it only showed 3.9V. and CC703 (100uF6V) only had 2.2V. no idea what those caps do.
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vref and video drive filter
the voltages look good
check the resistance to ground good and bad (no power) of pin2