Audio, caps, the wonderfull :)

[MNKyDeth]

Ok, so I just got done recapping a PC Engine Duo.

The I fired it up and the cd-rom read right away. During the intro of a game disc I could here crackling, popping in the audio.

I swapped it out for a HuCard and I had the same issue. The only real difference is that the static sound kept getting louder and louder.

I grabbed a headphone set I have here and placed it in the headphone jack and it was almost crystal clear. So...

I started poking around in the audio section assuming I had a bad trace someplace. A few more attempts and testing the audio and one of the caps popped and started bubbling. This is a brand new cap mind you.

I quickly shut off the system and then removed that cap. I have a couple more of that flavor, 330uF 16v for location C305.

Once I had another new cap in I tried the system one more time and now I have no audio in the headphone jack or through the A/V port. So, I am assuming I have a bad chip or chips now but that there is also a short someplace.

I went back through to double check all the caps to make sure none were put on backwards and they were not. I use almost all ceramics and only use Electrolytic on the thru-hole locations. So the few that there are they all look like they have the proper orientation.

I guess the question is:

Should I be looking for a short or something else that could cause this?

[Vimtoman]

Replacing SMD electrolytics with ceramics is not a good idea.

[MNKyDeth]

I have been using my US Duo for the past year on Ceramics and Electrolytic mix with the same exact caps that I used on this Duo.

I understand the concern but having done 4 Duo's and this one being the 5th with ceramics I would find it odd that is what caused this problem.

[Keith Courage]

most likely there are just some broken connection somewhere due to old cap damaged at some point.check the voltage on the 10uf caps and the one 22uf cap near the a/v jack. they should all around 3.85 volts. if they don't then there is either a broken connection to one of the capacitors or a possible bad connection to the op-amp which is right by the AV Jack as well.

[thesteve]

the burst cap was either a defective cap or reversed

[MNKyDeth]

Well, I would like to think I would not make that mistake of reversing the cap. But I guess it is possible. I didn't look real close as I was trying to get the cap off the board asap so no fluid from it would get on the board.

I do have a trash Duo board that I know I cannot fix as most of the super small caps or whatever they are look like they were scraped off or burned off around the board. But all of the chips seem to be there that I can use to try and replace the ones on this board.

I wish I could tell which one I need to replace. Guess I will just start with one and keep trying.

[thesteve]

i dont expect you have a chip issue, your best bet is looking at the voltages around amps, to find the effected area as described earlier

[MNKyDeth]

Yep, most all of the caps on the huCard side of the 7805's seem to have around 5v

Almost all the caps on the side by the A/V jack over to about the Supercap all read .44v or less. One or two were at zero.

If I measure down the side by the headphone jack all of those are .44 to .55v except C884, that one is at -2.24v

All of the other caps that I checked randomly on the board were between 3.51v and 5.03v

So... Looks like I am going to retest the traces in this entire area and hopefully find the culprit or swap out, reflow the 7805 to make sure they are seated properly. The heatsinks were extremely hot so I assume they both were working. I don't have a temp gun so I can not say exactly how hot they were.

[Keith Courage]

The 7805 regulators rarely ever need a reflow. Also, the system most likely wouldn't turn on and or even load a game if one of them were bad.

Look for broken/bad traces.

[MNKyDeth]

Ok, so since I started this thread I have tone continuity tested every inch of this board it seems like. I have another Duo board here that has no caps on it and I was using that as reference to make sure that if I did or did not get a tone that the trace was not getting a connection.

I literally followed a known cap that was not getting the proper voltage all the way back to one of the 7805's. I then went the other direction and it landed in one of the 4558 1714 IC's. I then followed the positive charge and the hole under the chip and still had no real luck.


Instead of doing tone continuity tests for the traces is there a better way to go about this?

I was thinking of doing it all the way with the power on so I could check the voltage all the way around the board but that is extremely difficult when the system is plugged in.

Any tips, hints, secrets to help find the problem spot?

[thesteve]

with the board separated from the housing, no cd mech
power on, check voltages to ground (ground is on the 7805 heatsinks and several screw holes)

[Keith Courage]

Did you try removing the op amp near the AV jack? Usually when no audio at all exists removing this op amp, cleaning under it and reinstalling can fix it. However, sometimes a new op amp is required if the contacts for it are bad.

I have labeled where 3.8V and ground should be for the op amp nearest the AV jack here. http://postimg.org/image/72gr79lvb/

You can also check ground by just bridging a wire to another ground while the system is on to hear if audio kicks back in.

[MNKyDeth]

Ok, so I spent a while this morning trying out the suggestions.

I had tested the caps before touching positive and negative sides. It yields the same results as touching the positive side of the caps to ground on the heatsinks of the the 7805's.
Most of the caps are around 0.5v when doing this.

I then removed the OP-AMP at IC506 cleaned the contacts and area with electrical cleaner and a scratch brush. I then tested again with the original amp, same issue. I then took one from the other board I have here and replaced it but still the same, no sound. The voltage at the 3.8v legs is 0.544v.

I also replaced the one by the headphone jack just to see if I had any change in that location as well. Grounding the ground leg on the op amps to a different location did not change anything as well.


Anyways, I literally just started replacing chips on the board. Starting with the ones nearest the cap that popped and started leaking when I first did the recap.
After replacing the IC506 Op-Amp, then I swapped out the IC505 item. Still no luck.

I then replaced the little black chip, no idea what it is, that sits between just to the back of the PCB at C305 and C306. Low and behold, I now have a fully working PC Engine. WOOT!!

No idea what that chip is but I noticed I was getting the 3.785'ish volts from the exact same chip that is right next to the audio connector. After Kieth mentioned, showed in the pic the 3.8v to the op-amp I realized I was getting the same voltage from the corner of that black chip all the way to the op amp.

I would have replaced a lot more chips but at least I found the one I needed. Many thanks to all that helped me. I really do appreciate it.