Failed (?) attempt at PCEngine Scart mod

[teknogrebo]

Hi,

First of all, I'm kind of hoping that this is a non judgemental forum, as I am not an electronics expert, I know how to solde and can follow a diagram, but that's pretty much it.

I have an original white pc engine system that I wanted to wire up a scart lead to as I dont have a japanese TV.  I read all the instructions for RGB mods on this site and had a pretty good idea of what I was up against.  Unfortunately I couldn't get a round 9 pin Din plug as Maplins (UK version of Radio Shack) don't sell them, so I went for an 8 pin variant, thinking that I could use the same pin for audio ground and video blanking ground (scart pin 4 & 18).  This may or may not have been my first rookie mistake.  I don't know.   I took out the RF unit as I wanted to use the space for the din plug, as I don't have the means to cut holes in the case.  2nd mistake? Possibly.   I wired all the connections up, connecting my combined ground to a pin that the old RF unit was using thinking it was 'groundable'.  This may have been my 3rd mistake.  

The end result is that when I turn the console on, the TV changes to the correct AV input, but I get the correct audio but with a loud hum that sounds like hi-fi earth hum.  I also get a black screen with vague distortions that change as the game display changes, so some sort of video signal is getting through.  I have triple checked all my connections, made sure that I haven't accidently shorted any lines on the PCB, the only other thing I can think of that may be of some note is that I didn't reconnect the big thing (that I assume is a heatsink) that covers the PCB.

Can anyone tell me where I may have gone wrong, and what I can do to check/rectify it?  (Without being judgemental).  The PC Engine was a birthday present from my wife and I am rather desperate to get it working.

Thanks in advance, and sorry about the long post!

[NFG]

Stop telling us not to be judgemental!  You suck!

First, check that you've actually tied your GND wire to GND.  That'll cause all sorts of problems.

The heatsink is not required for short bursts of play, but for sessions over 20 minutes you might want to consider putting it back.

Next, check your wiring.  Then check it again.  Almost all failures when modding are a result of wiring errors.

[teknogrebo]

Stop telling us not to be judgemental!  You suck!

Lol

First, check that you've actually tied your GND wire to GND.  That'll cause all sorts of problems.

I will double check this.  The hum does sound like a GND problem, so I will check those.

The heatsink is not required for short bursts of play, but for sessions over 20 minutes you might want to consider putting it back.

Yeah.  I only left it off as I thought I may have to go in there again, so I didn't want to keep taking it on and off.

Next, check your wiring.  Then check it again.  Almost all failures when modding are a result of wiring errors.

I did triple check.  But I should probably check again.

One thing I did think of last night, is that I didn't put in any of the amp units as the instructions are a little vague about whether it is actually required.  Is it possible that my TV needs the sync signal amplified?  If so, where should I draw the voltage from?

Thanks.  

[Aidan]

Loud hum and distorted signal isn't a good sign. Check the signals (and grounds) you're tapping with a multimeter, to ensure you're not accidently trying to tap a power line. Overloading the PSU will result in nastiness rather similar to this. You might want to back off your mod, and apply it step by step starting with something simple like the audio and working your way up from there. At least that way you'll be able to figure out what's going on!

I presume the unit worked properly before you tried modding it?

[teknogrebo]

Loud hum and distorted signal isn't a good sign. Check the signals (and grounds) you're tapping with a multimeter, to ensure you're not accidently trying to tap a power line. Overloading the PSU will result in nastiness rather similar to this. You might want to back off your mod, and apply it step by step starting with something simple like the audio and working your way up from there. At least that way you'll be able to figure out what's going on!

I presume the unit worked properly before you tried modding it?

Well the seller said it worked, but seeing as I don't have an NTSC tv, I couldn't test it without doing the mod.  I have now sourced an AV Booster which I am hoping to use instead of modding the unit.  However, I have just tried the booster out and I am just getting sound with no picture. So either:

a/ The mod is broken so I just need to take it out again (I will try this later)
b/ I broke the unit in the process of modding it (I hope it's not this one)
c/ The unit was broken in the first place (I hope it's not this one either)

Either way, I think I have realised that I'm not cut out for this console modding business, and I'm rather regretting attempting it in the first place.

[EDIT] Well I've just tried unsoldering all my wires and the thing is still broken, so all I can assume seeing as I have (possibly misguided) faith in human nature, and no trust in my abilities any more, is that I broke my engine

[Rockard]

heh!

Funny his, I very recently tried exactly the same thing!

Removed the rf-box and put an 8din there instead... looks reeeally nice when finished.

I wired the stuff correctly to the connector on the back.
No problems! With some amplifiers to the video (and soon also some to the weak stereo signals) the picture and audio worked fine!

How did (if you ever did) did you get the 8-din in place? did you glue it there, or what were your plans? I used the rfbox metalcase, and put it inside it with a small pcb.

I can put a small piccy up of my modd if anyone is interested..