Centipede/Electrohome Help Needed

FrizzleFried

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OK, so I pull an Electrohome G07 from a Centipede...it's blowing the small fuse. I have a 2nd electrohome chassis working, but needs a cap kit so I figure I'll rebuild the known working chassis and hook it up to the Centipede tube as it has Centipede burn.

Well, this centipede uses the single 6 pin connector, and I'd assume that it would be plug-n-play with this 2nd chassis, but nope... I can't get sync for some reason. As I adjust the H-hold, I get to a point where the picture is semi-clear, but somewhat angled and scrolling upwards and sideways at the same time. Typical "not synced" symptoms. But why? Why would I need to bust out the sync wires and run them to the 2nd smaller connector when it evidently worked fine with the other G07 chassis (there is no 2nd smaller connector in the cab).

Is this typical? Any other ideas?
 
Centipede uses positive sync, that is why there is only one 6 pin plug. The chassis that you have installed that won't sync up probably has a bad ground connection on the 6 pin header at pin 4.
 
Centipede uses positive sync, that is why there is only one 6 pin plug. The chassis that you have installed that won't sync up probably has a bad ground connection on the 6 pin header at pin 4.

I'll check, but I reflowed all headers.
 
Perhaps is one of those chassis a "wide chassis" and the other a normal chassis?

Did you get one of the chassis that had the wrong resistors installed in the sync circuit by the factory?
 
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Perhaps is one of those chassis a "wide chassis" and the other a normal chassis?

Did you get one of the chassis that had the wrong resistors installed in the sync circuit by the factory?

Not sure on either point. How do I check for both and or work around them?

I can say that the original tube had Scramble burn-in. Not sure if that helps.

Oh, and when I did the cap kit, I did the sync mod... for the curl.
 
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Welp, I am stuck. I've tried everything I know how to do. I've tried changing the sync to negative... no go. I tried tying both sync lines together... no go. I've reflowed the reflow of the headers... no go.

The history of this chassis: I know the tube it was on had Scramble burn in. It also was working (had red issues) with Dynamite Duke playing via composite sync at the small header and it synced.

I just can't get this bastard to sync for Centipede. Colors seem right... or mostly right... just no sync.

What next?
 
Check the values of R314 and R317 and report back. They should be 390-ohm resistors, but the factory made a mistake on some and installed 4.7k-ohm resistors....
 
Check the values of R314 and R317 and report back. They should be 390-ohm resistors, but the factory made a mistake on some and installed 4.7k-ohm resistors....

How does one determine what size a resister is? I know it has something to do with the bands, right?
 
Also, you could try swapping out the horiz frequency or vertical hold pots from the other chassis...
 
How does one determine what size a resister is? I know it has something to do with the bands, right?

If the colors are yellow/violet/red/gold (or silver), then they are wrong.

Of course, you could always put a meter on them, too...
 
R317/R314 are Orange/White/Red/Gold

I think you mean Orange/White/Brown/Gold.

Every game runs a little different on the frequency. If Dynamite Duke ran as composite negative sync, and Centipede runs on positive sync, then it's possible there's an issue.

Check the 5-pin connector from the chassis to the neckboard. Also, check all the wires from that chassis to the neckboard. Sometimes they break loose or are barely hanging on.

And inspect the entire 300 circuit from the positive sync inputs until it goes to the neckboard (and inspect that, too) for cold solder. Sometimes, you'll find some corrosion on the legs of those transistors and some may have broken off right under the transistor body where it's hard to see....
 
Double check the polarity of C302, it is screened right on the top of the board and wrong on the bottom of the board.

I know...I always use the top anyway. :)

I just checked Dynamite Duke out and it's out of sync now too... so it appears I've managed to screw up a component/solder joint/something. I'll pull the chassis again tomorrow and take a look.

300 circuit eh?
 
Solved!

Yup... I am a dumbass (for those who weren't already "in the know".)...

C501... you know... the ceramic that you pull from C303 I think it is and relocate to C501 for the sync upgrade...

...well, my dumb ass didn't solder it in! I blame the fact that it was a used part without long leads as the reason, but the simple truth is that I just didn't see it and it didn't get soldered.

Guess what. Sync works now.
 
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