sanyo 20 ez problems

elfyhead

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bought a non-working DK3, along with a DK logic board set (the whole thing was a throw-in on a purchase of a q*bert, and the cabinet is in good shape, and the monitor looked to be in good shape as well).

the monitor didn't come on at all. so i took it out of the cabinet, and took the boards completely off the monitor to check things (man that is an awkward board set to work on!). following the troubleshooting guide, i found a bad resistor at R601, so i replaced that, and i thought while i had the boards out i'd re-cap it as well (with bob roberts' deluxe kit). when i was done with that i thought i'd plug it in before i reconnected everything, to save myself the hassle of having to take it all apart again, but when i did it immediately blew the AC fuse.

now, i admit to being a neophyte when it comes to power circuits (i have an EE degree, but all digital except for a power lab class 25 years ago, and i haven't been using *any* of it in practice for 20 years or so), which was maybe why i thought i'd be able to test the circuit without the monitor attached. was this a really stupid thing to do? and if so, will it be OK to just replace the fuse, hook everything back up, and test it then? or is it OK to test the circuit not attached to the monitor itself, and the AC fuse blowing is just an indication of something bad elsewhere?

thanks in advance.
 
Wow. Another one. How many EZ20's can we pop before chassis prices double?! :p

I'm betting he/you plugged it in direct to the wall....as usual *sadface*
 
You may have gotten lucky, but I seriously doubt it. Replace the fuse and plug it in to the correct place in the bottom of the cab and see what you get.
 
You may have gotten lucky, but I seriously doubt it. Replace the fuse and plug it in to the correct place in the bottom of the cab and see what you get.

yeah, that's what i intend to do. the fuse blowout was immediate (never even got the plug fully into the socket), so maybe the rest is OK. all the isolation transformer does is filter out the noise (and DC on the input line); seems to me the fuse should take care of that, what else would blow? ah well, will find out tomorrow (and will plug it into the transformer...).

just to be sure though, i can check the circuit without having it attached to the monitor itself, right?
 
wall outlet is 120vac and the outlet in the bottom of the cab is 100vac

right you are. i was thinking of a traditional 1:1 isolation transformer. still seems like that shouldn't be a huge issue - the rectifier circuit should handle it. though i guess if too much DC was applied to IC601 i might be a sad panda (though the DC fuse is before that). keeping my fingers crossed...

EDIT: couldn't find a 4A fast acting ceramic fuse at any of the open stores today, so it'll have to wait until wednesday. still keeping my fingers crossed.
 
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got some replacement AC fuses and fired it up this morning (after connecting it to the in-cab socket, which in mine supplies 108 V).

it blew the fuse immediately.

any advice on where to look now (besides for a new chassis :))?
 
Don;t feel bad - this sort of thing happens all the time.
Buy a new HOT, new fuse, voltage regulator and possibly a flyback ;)
 
OK - thanks guys. at least i know where to start now. and the HOT is T452 (the F5024)? sorry, i'm still pretty new at this.
 

fantastic - thanks! and thanks for your patience. i was confused because on the circuit diagram it has "HORIZ. OUTPUT TRANS." by the T452. but i see from your diagram that T452 is the actual flyback. i visually inspected the flyback and it looks OK to the eye. maybe i got lucky on at least that bit. will test the Q902 tonight or tomorrow.

EDIT: resistance between the case of Q902 and ground is 11k ohms, so that seems good. but F302 was blown, so it's off to the store again tomorrow for a replacement for it.
 
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but F302 was blown, so it's off to the store again tomorrow for a replacement for it.

put in a new DC fuse and plugged it in this morning and the AC fuse (F301) blew immediately. given the HOT is OK does that mean it has to be a bad flyback?
 
fantastic - thanks! and thanks for your patience. i was confused because on the circuit diagram it has "HORIZ. OUTPUT TRANS." by the T452. but i see from your diagram that T452 is the actual flyback. i visually inspected the flyback and it looks OK to the eye. maybe i got lucky on at least that bit. will test the Q902 tonight or tomorrow.

EDIT: resistance between the case of Q902 and ground is 11k ohms, so that seems good. but F302 was blown, so it's off to the store again tomorrow for a replacement for it.


You have NOT determined anything here. You don't measure a HOT using resistance. I will guarantee that your HOT is blown.
 
You have NOT determined anything here. You don't measure a HOT using resistance. I will guarantee that your HOT is blown.

after going back to the flowchart and remembering how to read properly (sorry :/), i did the diode test, and it came back OK. but believing you know what you're doing, i desoldered the HOT off the wires (wire-wrapped, oh boy!), and went and bought a new one (NTE89 for anybody that cares about the cross-reference). the resistance measurement across the two pins is about twice as high on the new one (~40 ohms on the old, ~80 ohms on the new), but i don't know if that really means the old one is bad. anyway, i'm warming up the soldering iron now to put it in circuit...

i also found a fantastic set of generic CRT repair web pages at http://www.kellerstudio.de/repairfaq/sam/monfaq.htm (and related ones pointed to from within it) which is giving me some ideas of other places to check if needed (like the posistor, which i would not have thought of otherwise). you guys probably already know all of the stuff there but for me, coming into it new, that web page is gold.
 
put the new HOT in, and the AC fuse still blew rather quickly, but the tube did actually crackle to life this time. so i guess i can count that as progress (silver lining and all). thanks dokert for setting me straight when i veer madly from the proper path.

off to check some other possible shorts in the circuit (posistor and diodes in the bridge rectifier first i think)...
 
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