Sanyo 20EZ is blowing cap C467 [NOW FIXED!]

TheYeti

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Too long, don't want to read: My recently capped Sanyo 20EZ keeps blowing cap C467. I'm thinking it might be the Flyback causing it. I have since replaced the flyback with a repo and cap C467 still explodes.

Fully story: I recently replaced all the caps in a Sanyo 20EZ. (The monitor already worked but the picture was squished down the middle...basically foldover). This was the 5th monitor I've capped and the 4th Sanyo.

Everything seemed to have gone really well after my cap job. I fired up the monitor inside the machine. At first the image was super bright and whacked out. But after the usual pot adjustments, I got the pictured dialed in perfectly.

I had the monitor on for about 30 minutes just playing the game. During that time, I shut it on and off maybe a couple times. Again, everything seemed fine. I wanted to let the monitor run for a while before I took a reading on the B+. But after about 30 minutes, the picture looked so good, I just shut the game down and left it be.

Then after a couple days passed, I went to turn the game back on and nothing shows on the screen, but after a few seconds pass, I hear a faint popping sound followed by a hissing sound. Then up rises a puff of smoke. Of course, I quickly turned off the game.

I removed the monitor from the game and then removed the chassis to start figuring out where that smoke came from.

I quickly realized that cap C467 had popped. I know this normally happens when a cap is installed backwards but I definitely installed mine with the stripe in the correct direction. So I figured...well I must have just got a bad cap or something so I installed a new cap at C467. I also inspected the board for any cold solder joints and also checked to make sure each cap had the proper value and polarity. I also tried to make sure I didn't bridge any solder pads that shouldn't be bridged. I really tried to look over this board to make sure it was good to go.

So I installed it back into the game and turned it on. Nothing comes up on the screen whatsoever and after a second or two...POP!...yes, the same C467 popped again. So I shut the game down again.

I pull the chassis out again and start really looking closely at everything. As far as I can tell, every resistor and diode near C467 checks out OK with my multi-meter.

The only think I can think it might be at this point is the flyback. The negative side of C467 traces directly back to pin 8 on the flyback. Also the flyback has some of that leakage on top of it. Also, I've seen other Sanyo flybacks with this same hole, but it sure looks like a hole in my flyback. (see red arrow in picture below)



I guess another clue would be that if you recall, the monitor worked fine and looked great for about 30 minutes after I initially capped it. So I must have successfully capped the monitor right? Then something coincidentally failed after I turned the monitor back on a couple days later perhaps. Maybe the new stronger caps stressed out the old flyback?

Something else worth noting is that when I go to discharge the monitor, there is still a loud pop sound under the anode cap. If a flyback goes bad, does it still have a strong discharge? Does this sound like a bad flyback or something else? How would I know if a flyback is bad? Is there a way to know besides holes and cracks?
 
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NOTE: that is in the top of every flyback.

Thanks for confirming the "hole" on the top is actually normal. I'm really surprised because it looks melted around the edges.

So now I'm looking that the Sanyo 20EZ schematic and I'm trying to make sense of it. This is my first time trying to look at a schematic so I'm like a fish out of water. But I'm trying to learn. I've found capacitor C467 and highlighted it on the schematic.

If this cap keeps blowing, what component(s) would you test?

The reason I ask is because I felt like I have already tested every diode and resistor near C467 and they all checked out good. But perhaps I'm missing something.

 
I'm no expert but I'll wade in:

You said you checked resistors and diodes, does that include D454 and C466 (just below C467 in the schematic)? If either of those were shorted I would think you'd be reverse biasing C467 which might cause it to blow. If those are OK and you've checked everything else, yeah I'd say flyback.

It's interesting that C467 is a 160V cap. The operating voltage isn't anywhere near that high. Maybe there is a startup transient that warrants that rating. Anyway, you certainly can have a flyback that puts out too high of voltage. I had a 4900 flyback that was doing that.
 
I'm no expert but I'll wade in:

You said you checked resistors and diodes, does that include D454 and C466 (just below C467 in the schematic)? If either of those were shorted I would think you'd be reverse biasing C467 which might cause it to blow. If those are OK and you've checked everything else, yeah I'd say flyback.

It's interesting that C467 is a 160V cap. The operating voltage isn't anywhere near that high. Maybe there is a startup transient that warrants that rating. Anyway, you certainly can have a flyback that puts out too high of voltage. I had a 4900 flyback that was doing that.

Thanks for the suggestion! I'll take any I can get at this point! :)

Yes, I think that I verified D454 was OK. I pulled it from the board and checked that it was not flowing backwards. However, I will need to check again to make sure that neither D454 and C466 are shorted.

I really want to try and eliminate all other components before I replace the flyback. Obviously, I don't want to go through the effort of replacing a working flyback. :)

When I think of a "shorted circuit" I think of something I did...like bridging 2 contacts during soldering.

However, it sounds like if a component fails, it could also create a short? I guess this is a dumb question because if a diode fails, then it can send voltage in the reverse direction...aka "short"

But if a resistor fails, does that ever cause a short?
 
Yes, a failed component can cause an internal short within the component. Capacitors can short out internally where the two films physically touch and now it just acts like a wire and not a capacitor at all. A resistor can fail causing electricity to no longer be resisted and also act as a short. Or, a resistor can fail and cause more resistance to be present. Thus putting greater strain on an separate component further down the line.

Those are things you'd need to be on the look out for. Especially any components one or two places down the line from the negative and positive leads of the cap that keeps blowing up.


Thanks for the suggestion! I'll take any I can get at this point! :)

Yes, I think that I verified D454 was OK. I pulled it from the board and checked that it was not flowing backwards. However, I will need to check again to make sure that neither D454 and C466 are shorted.

I really want to try and eliminate all other components before I replace the flyback. Obviously, I don't want to go through the effort of replacing a working flyback. :)

When I think of a "shorted circuit" I think of something I did...like bridging 2 contacts during soldering.

However, it sounds like if a component fails, it could also create a short? I guess this is a dumb question because if a diode fails, then it can send voltage in the reverse direction...aka "short"

But if a resistor fails, does that ever cause a short?
 
Yes, a failed component can cause an internal short within the component. Capacitors can short out internally where the two films physically touch and now it just acts like a wire and not a capacitor at all. A resistor can fail causing electricity to no longer be resisted and also act as a short. Or, a resistor can fail and cause more resistance to be present. Thus putting greater strain on an separate component further down the line.

Those are things you'd need to be on the look out for. Especially any components one or two places down the line from the negative and positive leads of the cap that keeps blowing up.

Ah...ok, thanks for explaining that. :) Makes sense. I really shouldn't take anything for granted. For example, there is a cap (C468) sitting right next to C467. They are in the same circuit. It's a brand new cap of course, but I suppose that could be bad too. Even though it didn't pop.

It's the "components one or two places down the line" that scares me. These circuits branch off into several directions very quickly and I get overwhelmed. It's like trying to find a needle in a haystack. I'm sure someone who knows what they are doing could find the faulty part(s) in less than 60 seconds. LOL!

I have an extra working 20EZ chassis I'm going to pull out so that I can compare with it. I need something as a reference point because I feel like I'm working blind right now. :)
 
So I have been scouring the internet trying to find all content related to the Sanyo 20EZ flyback.

I eventually stumbled upon an an archived Bob Roberts page hosted by thegleek.com

On this page, Bob is describing how he replaced a bad flyback on his Sanyo 20EZ. And wouldn't you know it!? ....he shows a hole in the top of his flyback awfully similar to the hole in my flyback:

Bob's Flyback hole:


My Flyback hole:


I also pulled a known-working chassis from my other Nintendo game last night and this hole DOES NOT exist on that flyback.

This would further support the theory that the flyback is causing my problem, yes?
 
I'm back for an update...

#1 - I epoxied over the that hole in my original flyback and that didn't help. Cap C467 still explodes.

#2 - Gave the chassis to my father-in-law who is somewhat familiar with circuitry and electronics. He couldn't find any components that looked out of spec.

#3 - Completely replaced the original flyback with a reproduction flyback and Cap C467 STILL EXPLODES. :(


So I guess it's safe to assume that my original flyback was fine and was not causing C467 to pop.

I'm now totally lost. I have no idea where I should look next. And now I'm sad.

This Sanyo 20EZ issue is going to be the death of me.
 
I'm back for an update...

#1 - I epoxied over the that hole in my original flyback and that didn't help. Cap C467 still explodes.

#2 - Gave the chassis to my father-in-law who is somewhat familiar with circuitry and electronics. He couldn't find any components that looked out of spec.

#3 - Completely replaced the original flyback with a reproduction flyback and Cap C467 STILL EXPLODES. :(


So I guess it's safe to assume that my original flyback was fine and was not causing C467 to pop.

I'm now totally lost. I have no idea where I should look next. And now I'm sad.

This Sanyo 20EZ issue is going to be the death of me.


I would suspect that one side of the cap is low ohms to ground

confirm there is high ohms on both sides of the cap or on trace TP's

is the ground side cap low to ground?

check the trace along side of the chassis is not cut or being grounded

by the chassis frame and r470 is not touching ground.

the trace run from the flyback area to the horizontal drive transformer area.

see the trace along the edge of chassis could be shorting on the trace.

check it out Good Luck!

The cap should have high ohms to ground on both sides of the cap!
 
I would suspect that one side of the cap is low ohms to ground

confirm there is high ohms on both sides of the cap or on trace TP's

is the ground side cap low to ground?

check the trace along side of the chassis is not cut or being grounded

by the chassis frame and r470 is not touching ground.

the trace run from the flyback area to the horizontal drive transformer area.

see the trace along the edge of chassis could be shorting on the trace.

check it out Good Luck!

The cap should have high ohms to ground on both sides of the cap!

Thanks for posting this suggestion!

However, I waived the white flag and called in the big guns.

I shipped my chassis in for repair this morning to KLOV user paul400

I'm hoping he can sort out this mystery. If he gets stuck, I'll make sure your suggestion above makes it to him.

Thanks again!
 
chassis has been repaired. this one was a little of an oddball.I spent a couple hours checking parts and could not find any out of spec. It would still power on but when powered off I noticed the HOT was heating up very fast but not blowing the fuse. I also noticed the flyback and focus knobs were HOT! I disconnected the wires and checked and found it was shorted!!! replaced and is now working. I have never seen one of these go bad.
 

Wow! That is some amazing detective work! Yea...I'm really glad I sent you my chassis.

I would have definitely not figured that out. :)

Seriously...that's some really top notch work figuring out that issue!

And a big "THANKS!" for posting the video explaining the problem and the fix.

I's a real bummer (but also a reality) that more and more uncommonl parts will start failing on these 30+ year old chassis.
 
Whoah, nice fix!

Just for future reference (in case that youtube video goes down), this was caused a shorted flyback controller (the controller that houses those two white knobs to control focus and brightness on the flyback). Replacing the controller corrected the issue and the HOT and C467 cap stopped blowing.
 
I'm not sure who created/updates the Sanyo 20EZ flowchart but this would be a good step to add to it.

Obviously this is not a common part to fail, but adding it to the chart could really save some others down the road a ton of grief. It could also save some chassis from being tossed aside as unfix-able "lemons".
 
the flowcharts are a great way to start troubleshooting, just to point you to the right circuit. sometimes they are dead on, other times you have to dig deeper into that circuit to find the bad component.
 
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