PCEngineFans.com - The PC Engine and TurboGrafx-16 Community Forum
NEC TG-16/TE/TurboDuo => TG/PCE Repair/Mod Discussion => Topic started by: grendelrt on April 30, 2015, 02:16:18 PM
-
So I started a full recap because the music for cd games was too low, you can hear it but the sound effects are about 2-3x as loud. I found a bunch of dead caps and replaced everything
but 4 caps between the card slot and the large heatsinks since my region mod is in the way (C522,C519,C521,C525). Started the system up and it plays fine , looks fine, but the sound is still low on CD and I have lost left channel even on hucards. Since I have replaced basically everything it doesn't really narrow it down to what could have been the issue. Anyone have some advice on which caps to look at for the 2 issues I am still having? Thanks for any help!
Edit:replaced the last 4 caps
-
There must be bad traces somewhere. Double check the voltage on each cap above the two heat sinks to make sure their traces are getting a connection.
Also, could be a short in an op amp somewhere due to old cap corrosion but check the cap voltage first. Most should be 3.8V or higher. Anything below that isn't good.
-
C604 and C610 were 2.8 v but everything else in the area looked to be 3.8 and higher, I couldnt check the non surface mounted stuff while the board is running. Could those 2 be causing the issue?
Edit: Been also reading on the forums that sometime the 4558 can cause this issue, is there a way I can test these? Also since HuCard sound is normal , could the low CD sound be laser related at all?
-
generally the low CD volume is due to bad caps or bad traces around said caps. However in some rare cases it can be bad traces near the CD drive itself. Much more rare. double check all connections for caps in this area circled in blue.
(http://s24.postimg.org/qw4agpq79/PCEngine_Duo_Total_Cap_Replacement_Refer.jpg) (http://postimage.org/)
screen shot (http://postimage.org/app.php)
As far as loosing one of the audio channels for the Hu card games double check the two Caps closest to the AV port and make sure both have the same voltage.
-
Thanks for the help =) Of those caps you circled , the bottom 22uf cap was really bad underneath when I removed it yesterday. I removed some pcb at the hole attached to that solder pad and soldered the leg of the cap to that and then ran a line from the ground leg of the cap behind it to ground it. I was getting plenty of voltage through this cap last night when I tested, but maybe I didnt repair this area correctly.
Repair
(http://pic.photobucket.com/bwe.png) (http://s63.photobucket.com/user/grendelrt/media/20150501_102552.jpg.html)
Original Damage
(http://pic.photobucket.com/bwe.png) (http://s63.photobucket.com/user/grendelrt/media/20150430_105858.jpg.html)
I flipped the board and did find this one area with a black mark on a trace, I tested continuity between the jumper and leg around it and got continuity.
(http://pic.photobucket.com/bwe.png) (http://s63.photobucket.com/user/grendelrt/media/20150501_102055.jpg.html)
-
OK may have found something else, not sure if its an issue or not. I hooked my probe to the main ground strap that attached to the cd rom board and started testing the ground legs on the caps in that area. The five caps below (one you cant see its small behind the left cluster) I dont get continuity from the ground strap on the left leg. I took a small piece of wire and connected one leg to another that was getting continuity, then that leg started getting continuity. Weird thing is when I run the machine and use the left leg as negative and the right as positive I still get a good volatage reading of 3.8v. So I am guessing there are maybe two seperate ground planes?
(http://pic.photobucket.com/bwe.png) (http://s63.photobucket.com/user/grendelrt/media/20150501_112722.jpg.html)
-
Fixed my missing left channel of sound :) Found a bad solder joint in the audio section. I dont think my CD sound issue is fixed though from that, I have very low cd background music sound + normal sound effects volume. Is there any way to run the CD with the cover off, I saw a pic where someone had removed the spindle magnet from the top cover or had a spare but wasnt sure if that was possible.
EDIT : Found the guide to remove the magnet,
http://console5.com/wiki/Turbo_Duo
I have spent a lot of time continuity testing each trace in the sound area with no luck so far.
Things I am wondering about that may affect the CD sound.
1) RGB mod was added around same time, could the 5v line be messing with anything? I used the side of C532 to get 5V.
2) R687 came off during cap replacement but I soldered it back on, could that affect anything?
3) Which 4558 op amps are responsible for the CD sound, I read IC506 is chip sound. Is there a way to test each of these other than checking leg 8 for voltage?
-
as for the amps check pins 1 and 7 on each
they need to be around 4V (3-5)
a bad voltage is almost always a problem feeding the chip, not the chip itself, but it tells you what chip is unhappy
-
I put in a hucard and ran it, these were the values I got, I think I got all the 4558s
IC 506 Near sound amp area
1- 2.9
7- 2.9
8- 7.75
IC 107 Beside cd rom area
1- 9.36
7- 9.9
8- 9.9
IC 203 Beside cd rom area
1- 3.8
7- 3.9
8- 7.7
IC 507 Near sound amp area headphone plug
1- 4.3
7- 4.3
8- 7.7
IC 521 Near sound amp area on back
1- 7
7- 7
8- 7.7
IC 503 Near sound amp area on back
1- 4.7
7- 4.7
8- 7.7
-
IC107 and IC521 have issues
start with IC107 as it looks like its missing ground
-
IC107 and IC521 have issues
start with IC107 as it looks like its missing ground
Thanks for the reply, it looks like Pin 4 is supposed to be ground, I did a continuity test on IC107 from a ground to pin 4 and had continuity (also checked for voltage and saw no voltage). Whats the best way to work backwards to figure out why the chip is getting (assuming) too much voltage?
-
they are opamps
so each chip is 2 amps
each amp has a + and - input
if you short the -input to the output pin the output must match the + input
thats a quick test of the chip
-
Thanks Steve, I tested IC107 and got
Pin 7 + Pin 6 = 5v
Pin 5 = 5v
Pin 1 + Pin 2 = 0v
Pin 3 = 0v
Pin 5 (IN+) and 6 (IN-) are both 5v and then Pin 7 (out) is 10v , so if pin 7 is 10v is it just adding the voltages and one of those should (5,6) be 0v? Sorry learning as I go on this one, havent dealt with the chips much.
-
the amp is a simple comparison circuit
if +>- output will rise until ->+
if ->+ output will fall until +>-
in practice when used as an amp a resistor must tie out to -, so - rises when out does
-
Head explodes. Lol. If they are both 5v why would it raise to 10v?
-
when +/- are the same the amp floats, output could be anything
-
Did you happen to know what feeds pin 5 an 6 on that ic? There is a chip in the way on the bottom of the board that blocks the view, trying to avoid bending it.
-
I resoldered the caps near IC107 ( thanks Keith!) and the voltage did drop a tiny bit, it went from
IC 107 Beside cd rom area
1- 9.36
7- 9.9
8- 9.9
to
IC 107 Beside cd rom area
1- 9.5
5 - 5
6 - 5
7- 7.5
8- 10
I tried tracing the path from the legs on the bottom of the board, i moved that chip that was blocking but didnt want to pull it up too much. I lost the traces though.
Pin 6 on IC 107 4558 - Bottom of board R134 to R140, then I couldnt find where it went next. '
Pin 7 on IC 107 4558 - Bottom of board R145 to R144 to solder joint that splits to R142 and R143.
Took some pics if it helps
(http://pic.photobucket.com/bwe.png) (http://s63.photobucket.com/user/grendelrt/media/20150508_140112.jpg.html)
(http://pic.photobucket.com/bwe.png) (http://s63.photobucket.com/user/grendelrt/media/20150508_140250.jpg.html)
This one looks really cool too ha!
(http://pic.photobucket.com/bwe.png) (http://s63.photobucket.com/user/grendelrt/media/20150508_140321.jpg.html)
-
SUCCESS! The via near the IC521 was bad! Wooo, finally ahha. Voltages at 521 went back to normal with a quick patch wire to ground.
(http://pic.photobucket.com/bwe.png) (http://s63.photobucket.com/user/grendelrt/media/20150512_150221.jpg.html)
Sound is good, and since the recap I think my video quality went up a little bit. Another duo is still alive, hanks for all the help! =)
-
as i said bad ground
-
as i said bad ground
Yeah it was just finding it! thanks for the help =)