elusive makvision 3129 issue

[lilshawn]

I have a Makvision M3129 that originally came into the shop (ticking power supply - no power) with a bad C30 capacitor (swollen and leaky top). upon further investigation found R50 out of spec and D19 shorted. Replaced both.
 
Powered up the chassis and the high voltage and deflection comes on again, but then made some strange warble sounds in the deflection, petered out and fried R50 again.

I've changed/checked/replaced several components being fed by this voltage rail to no avail...
 
Changed TDA1675A and it's power feed R113 (which was out of spec slightly as well.)
 
Checked diodes and resistors. All seems good.
 
I've gone ahead and replaced the HA17358 opamp with an LM358 opamp (only one I have in stock) and the chassis still cooking that R50 power resistor. I'm going to have to source some more 1.5 ohm resistors before I can continue troubleshooting.

I measured the inductance of the deflection yoke and it's seems about right and is not shorted.

attached is the schematic for the chassis. i've followed through the affected circuit and can't find any other fault.

any ideas?

[grantspain]

i think deflection yoke,i have had v defl faults on these and only has ever been tda1675a,d19 and r50

you could try it powered with vertical deflection attached

btw these yokes are very similar to nanao ms9-29,sanwa es31 and sanwa pm1745 if you have one of these tubes

[lilshawn]

yeah, i'll try booting it up with the vertical disconnected and see if it "works". I'm waiting for some more resistors to be delivered. I'm tapped out.

I measured the vertical yoke with an LCR meter and compared it to a near identical style and capability yoke for a Wells gardner monitor and the vertical is only a couple of mics off (8.28mH vs 8.10mH (on the known good)) being set up for different manufacturers would probably account for the few microhenry difference. The yoke could still have compromised insulation inside though that is not showing up until under high voltage. I'll have to check it out.

thanks for the tips, i'll start focusing my efforts a little more in this direction.

[lilshawn]

Got some resitors and got the unit fixed up again and powered it on without the yoke lead plugged on. I also monitored the voltage of the 25 volt line during testing.

Powered on the monitor and the voltage came up to ~17 volts DC and slowly began to fall as it continued to run. after about 10 seconds the voltage was at ~12 volts...

Something on the chassis was starting to smell warm so I powered off and and checked around but couldn't find anything hot. the resistor that normally burns up was warm but still in spec.

I did not notice a dot present on the screen but as i removed the chassis I noticed the HV lead wasn't quite clipped in all the way so it might have just been that.

I inspected the chassis again for signs of failure but have not found anything. Startin' to bug me. 

[lilshawn]

I've discovered some caps I purchased are counterfeits. (not sure where these came from but likely e-bay) they have actually put a "Rubycon" sleeve over a cheap chinese "SNE"  branded cap and heat shrunk it on... turns out one of the caps I changed (C58) used one of these fake caps and was, in fact, installed backwards (IE: the sleeve was placed on the wrong way around)    I only noticed the bottom was puffed out a tiny bit.

the fact it hadn't blown up was miraculous. Changed it out. I'll post some pics when I get home and upload them from my phone to the computer.

now i have horizontal deflection line but no vertical deflection. I'm going to see if i can get another TDA1675A and swap it out. maybe the power surges from everything screwed up and whatnots blew it out.

back to work 

[MonMotha]

I've discovered some caps I purchased are counterfeits. (not sure where these came from but likely e-bay) they have actually put a "Rubycon" sleeve over a cheap chinese "SNE"  branded cap and heat shrunk it on... turns out one of the caps I changed (C58) used one of these fake caps and was, in fact, installed backwards (IE: the sleeve was placed on the wrong way around)    I only noticed the bottom was puffed out a tiny bit.

the fact it hadn't blown up was miraculous. Changed it out. I'll post some pics when I get home and upload them from my phone to the computer.

I'm going to emphasize this for the next time somebody rags on me for recommending that they buy parts from decent distributors rather than eBay...

[lilshawn]

the pics (of another cap)

http://imgur.com/a/xczaG

[lilshawn]

Welp, I got another TDA1675A vertical deflection IC and fired it up.

Got a half decent picture and everything. 

Has some fold over on the top...not much though, maybe 10 scanlines. Have to find some notes on another unit on a fix and find the equivalent in this circuit. 

I can see the finish line...