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7800 av help (no sound)


Kaiju
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i am very new to modding and soldering, i did a few things around the house and took the jump to modding my 7800, now im having issues and worried i screwed it up for good.

 

i have video but no sound. any help or advice would be amazing.

 

 

i got the kit off ebay, and followed some guides i could find, but had issues one where/how to do the audio, the point on my board to solder in the audio wire loooked bad, like it had no solder on it to begin with

 

again, any help or advice, im at a loss..im a chef by trade, this is all way over my head, post-57179-0-85491400-1498281979_thumb.jpgpost-57179-0-14692700-1498281982_thumb.jpgpost-57179-0-39989500-1498281988_thumb.jpgpost-57179-0-35741900-1498282005_thumb.jpg

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I don't think the traces necessary look damaged; looks like lighting variances to me.

 

Anyway, question: have you tested with games using both TIA audio (most of the 7800 library) and those using a POKEY chip on-cart (Ballblazer and Commando, plus some few homebrews)? Most a/v mod instructions for the 7800 have you pull audio from the base of two resistors (one for TIA and one for POKEY sound), tie them together and balance the outputs with a capacitor or something, then wire a single line into the Audio Out.

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i tested both types of games an no sound. im having a hard time finding exactly where to connect the audio wire from the little kit board it would be the Green wire in the photo i circled, i put it there as per some other instructions

 

it also said to add a wire from C-10 (after removing) and go straight to the rca audio jack, which is what i did for POKEY but again like the normal audio , no photos \

 

If someone can let me know where to solder the Audio wires from the board to the jacks As well as the POKEY connections (my kit came with a capacitor)

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Look at my guide here: It was written up for installing the UAV s-video board, but the audio portion is universal for pretty much any audio out you want to run. This is how I wire up my audio and provided the capacitor you received with the kit for your audio is the same value 10uf - 16v or above, you could do the exact same.

 

https://www.dropbox.com/s/uv5hhtks3myxr4r/UAV_Installation_A7800.pdf?dl=0

 

I have pics in this guide showing the process I did, but basically you clip the north legs of both R5 and R6. Tie them together and then run the + of the capacitor from that, and then attach from the negative of the capacitor to the center post of your RCAs for audio. You get very balanced TIA and Pokey this way.

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i made a few adjustments while waiting for replies, but still not getting sound, here are some other photos.

 

Again this is my first project, and maybe the 3rd thing i ever soldered, so forgive the sloppy work and any misunderstandings.post-57179-0-77683000-1498341917_thumb.jpgpost-57179-0-34844900-1498341921_thumb.jpgpost-57179-0-14480800-1498341930_thumb.jpgpost-57179-0-82534300-1498341931_thumb.jpg

 

 

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Cross thank you. One of the guides had me clip off R5. Can I replace it with 620 ohm 1/4 watt 5% resistor as I have some around?

According to the schematics... R5 is a 6.8k resistor... so...no. a 620ohm won't do much if anything. I can't be sure which is which, but I know that one of the resistors there is for the TIA and the other is for the Pokey input off the cartridge. So if you have a Pokey enabled game (Ballblazer or Commando), then it would be interesting to see if you have audio at least from that. Provided you connect your RCA on the north end of R6.

 

Just to see if you can even get any audio, you can try and solder your audio output wire from the RCA centers, to the south legs of where R5 used to be and where R6 still is. If it works, then you know that removing that cap and the r5 resistor are likely to blame for why you haven't any audio from the point where you are trying to tap it from.

 

BTW I see your RF modulator is still attached? Do you still have video and Audio from that? I'm guessing not with all the other resistors that were removed but just curious.

 

Also in the future, when doing a mod like this and you aren't sure if it will work, I would suggest only clipping the legs of the resistors going back to the TIA and MARIA chips etc. This way, you still effectively removed them from the circuit, but can also easily reattach them in the future if you need to by just using a dab of solder to bridge the cut you made. I made this same mistake when I installed the LHE version of the 7800 mod. It requires you to remove about a half dozen resistors. But, then when I wasn't happy with the results that mod gave me, and I went to try others, I had to track down and replace all those crazy resistors LOL. So..yeap..lesson learned there.

 

In my example, you cut the north legs and solder them together with your audio out to the RCAs because that way, you are still getting the resistance that was provided by those resistors. As such, they were there to balance the audio from the TIA and Pokey then going through additional filter caps independently and eventually getting mixed back in the RF modulator.

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okay thanks so much, im going to remove the green audio wire from where i put it , and try it at R5/R6, ill test ballblazer and rf also, i just stepped out for some air atm...this stuff was making me panic..i fought with myself to even do something like this as i hate the idea of "ruining" an expansion slot 7800...

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There is no audio as the trace is broken in the 3rd pic on the first post. You need to repair that trace as it is a via on the board between other components. The point you tapped for the TIA (pic 3) was correct. The only issue is the broken trace from what I see.

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I'll look up how to repair it. Is it. Difficult process? Like is there a high chance I'm just going to make things worse

 

I assumed if I follow the broken trace to another point I can solder into it should of been ok. As in the second set of photos posted.

Edited by Kaiju
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Did what you asked cross, as per photo. Still no sound, no sound on ball blazer or from RF

 

As Shawn stated above, and In looking at the pics, they are correct. You have a missing trace on the board. You will have to repair that first. Easiest method is by using another piece of wire and soldering from the via where you first had the green wire soldered to the bottom of the small axial turquoise capacitor where you next had the green wire soldered.

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Hopefully yes. However, I tend to use thinner wire for traces repair and usually make my repairs on traces on the bottom of the board whenever possible. Easier to see it that way. Just have to find the vias from the top or points where to solder.

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Looks like your burning the heck out of your board. And possibly causing shorts between the circuts.

Try using flux and a very small tipped low watt soldering iron.

I would send away to a soldering pro or get another 7800 and embrace RF.

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Absolutely. It's like the pasta dish where one little mistake was made, where one ingredient was used a little too much. Not quite right. In in attempt to fix it, 5 other spices and flavorings and extra cheese are used to cover it up. In the end it's no good.

 

---

 

I find it funny the people perform mods to escape from RF, yet continually state they want original carts and consoles. RF is original and was what was intended by the manufacturer. Got news for you buddy. Mods are not original.

Edited by Keatah
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Reason was I'm moving and limited space. Can't take my crt.

 

Like I stated up top I am new to this, but glad I'm providing amusement to you guys. Thanks for the help for those that did offer it.

 

I will just get another 7800 for the family. And leave this project be till I learn more.

 

Btw. When did I say anything about Wanting original or anti RF buddy?

Edited by Kaiju
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The best advice not given yet is to set aside this mess. Get some scrap'n'crap hardware and buff up your soldering skills. Learn some troubleshooting skills and how to read a schematic if you don't know yet. Then come back and take it one step at a time. Verify and restore each point you touched. One step at a time. You could make this 7800 a restoration project or keep it for parts. Lots of options.

 

Unlike the pasta dish which is permanently ruined, this can be still be salvaged, with some work.

 

And you will gain valuable skills by working on shit boards for practice. The skills are (more and more) going to be important for folks like yourself that get into original hardware. Because you will need to be a-fix'n controllers and switches and connectors and even electronic components like capacitors and regulators. If not, then you'll be spending money on replacing whole consoles which are getting older and older by the year.

 

There's no way around it. Either do it yourself or hire out someone or replace. It's the nature of the beast.

Btw. When did I say anything about Wanting original or anti RF buddy?

 

Not directly. It's just common that people that mod want to get away from RF. And it's just common that people that play using original hardware like things as they were.

 

IMHO RF is the way the games were meant to be played. And if someone wants to get away from RF and upgrade, why not go all the way, do whatever it takes, to enjoy the latest and greatest display technology of today?

Edited by Keatah
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If you were at all closer I would offer to take a look at it and would only charge for my time assuming I can get it going for you. However, shipping a 7800 with properly packing and insurance is a $20 cost so it is really up to you. You can probably get another console only 7800 for what the cost in shipping to me and back plus a few hours of my time would run you.

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  • 2 weeks later...

post-37734-0-64665100-1499736232_thumb.jpg

 

I purchased the unit from the OP. Been working on it this evening. There was no usable path from where the jumper wire had been installed to TIA so, I jumped straight from the cap c14 to TIA but, I had to replace c14 first because the leg separated easily when I was cleaning the brown goo away.

 

Then I replaced R5 with a 6.8k resistor because, I normally join R5 and R6 on the North (up board) side and connect those to the audio input of the av board.

 

That got me TIA sound but no pokey. I noticed on closer inspection there doesn't seem to be any path on either side of the pcb leading to the south end of R5.

 

Just wondering if anybody knows off hand where I should try to pick up pokey sound on the 7800 board.

Edited by SIO2
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