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  #1  
Old 10-07-2015, 03:38 AM
StarquestMan StarquestMan is offline
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Hitachi CT13C2 vertical screen distortion

Ive got a small 13" color solid state hitachi that I recently picked up and have been using as a bedroom set. It works great but ive started to notice some issues with vertical linearity quirks like waviness on vertical shapes like buildings and menu screens. Its mostly noticeable when objects enter and leave the right side of the screen (like if im watching a youtube video where someone is at a workbench working on something and he reaches for a tool off screen the whole portion of the screen will stretch towards the right). The picture is also getting slightly fuzzy. I decided to open it up again and play with the focus control on the flyback (which didn't really help) and i noticed that one of the little capacitors (not sure what type it is since there are many types that fall into the tic tac shaped rectangle category) had gotten warm enough to melt its waxy coating over a 3 inch diameter area around it. It is at c712 next to a small transformer in case someone who knows these sets or has a service manual was wondering. I also wasn't sure if it is common practice to simply do a full recap on these aging sets like what is done with audio gear, i haven't come up with any treads on this when searching though and was wondering if some Nichicon Fine-Gold series caps would bring this set to as good as or better than new picture quality?
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  #2  
Old 10-07-2015, 10:55 AM
wkand wkand is offline
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Hitachi Waviness and Hot Cap

You do need the schematic, but while you are waiting...

The waviness suggests electrolytic filter caps in the power supply, but depending on where in the circuit the melty squarish cap is located, if it is a bypass cap to ground, you could get minor ripple in the picture like you are describing.

Change that cap that is getting hot or melting, but if you can, check voltages first on either side of the cap that is melting. It does not matter what the values are supposed to be for this test, so long at they are not identical or nearly so. That would indicate DC leakage. Also, remove the cap and check voltages after it is removed if you find that the voltages are the same with the cap in circuit. if they change after removing it, that is more confirmation that the cap is leaking.

the other thing to check for is a major difference in the DC voltage on either side of this cap. if, say the working voltage of the cap is 100 volts DC, and you measure a 250 volt difference between the two leads of the cap, that's a problem you need to check out, else the new cap will end up doing the same thing.

Replacing it is a matter of carefully reading any markings on it and deciphering them using the web or this group.
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  #3  
Old 10-07-2015, 12:15 PM
zeno zeno is offline
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Sounds like its a horz problem not a vert prob.
C712 is a .022 10% 100 V
Not big enuf to give all that wax IMHO.
The transformer may give enuf ( T701 ).
Part # for that is 2260021 prob have to find a junker for it.
Stuff you see may have come from outside. For some
reason people love to burn candles on TV's !!
Both parts are in the horz.
Do NOT run it long like this it could blow things out.
Other suspects are C904 & C701 both electrolytics.
C904 front of flyback ( FBT )
C701 to left of FBT
A few screen shots & a chassis shot can help us.

73 Zeno
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  #4  
Old 10-07-2015, 04:04 PM
StarquestMan StarquestMan is offline
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well i checked out that cap and it was reading 28v across it. i should mention that the waxy coating i found was very very thin like hot engine oil residue or penetrating oil of some kind it definitely was not candle wax, in fact the only reason i guessed it was wax was because i could see a glossy reflection on that wax dipped cap and was able to wipe it right off with my finger when the set was running. i did notice that some of the electrolytics near the flyback and power supply section were warm to the touch with the set running last night and i will definitely check them out since they tend to dry out especially with heat. i hope the pictures i uploaded will work. i dug out my pattern generator and used a crosshatch pattern that shows a bit of what is happening but i can definitely take more if needed.
Attached Images
File Type: jpg IMG_20151007_121814_669.jpg (53.4 KB, 46 views)
File Type: jpg IMG_20151007_121839_280.jpg (42.8 KB, 26 views)
File Type: jpg IMG_20151007_122931_346.jpg (85.5 KB, 51 views)
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  #5  
Old 10-07-2015, 04:19 PM
StarquestMan StarquestMan is offline
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well just after posting my last post i started looking at the residue pattern again and noticed that it may be coming from that dark brown Nippon Chemi-Con cap at c903 and running back towards the flyback making it look like its originating from the wax dipped cap next to it. now that i think of it this capacitor seemed to stick out as being the warmest cap i found.
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  #6  
Old 10-08-2015, 09:03 AM
zeno zeno is offline
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C903 is in 135V regulator so try it. Also check for 135 VDC at
pin 6 of the FBT or pin 7 of the reg module CP901. Must
be 135V !
BTW the screen shot dont show much, in the case use a
few real pictures.

73 Zeno

Quote:
Originally Posted by StarquestMan View Post
well just after posting my last post i started looking at the residue pattern again and noticed that it may be coming from that dark brown Nippon Chemi-Con cap at c903 and running back towards the flyback making it look like its originating from the wax dipped cap next to it. now that i think of it this capacitor seemed to stick out as being the warmest cap i found.
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  #7  
Old 10-20-2015, 01:47 AM
StarquestMan StarquestMan is offline
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sorry i took so long to get back to this thread. here are some more pictures i took unfortunately none are of a moving image because it was impossible to take a picture with my camera at the precise moment something would jump off/on screen but i did find some menus that had a bright section that would have a similar effect.

i haven't checked that 135v rail yet but i will definitely do that once i pop the set open again. is there a certain tolerance that is acceptable? i am very suspicious of the cap at c903 but i cant find any lying around that are high enough voltage so i will have to order it if it is in fact bad but i will check the 135v rail first. which brings me back to one of my original questions as to weather or not i should do a full recap of the set? also if i do will everything have to be completely re calibrated to compensate for the new caps or will it just be "better than original" and improve the overall sharpness and clarity of the set? i guess im wondering because i recently recapped an old pioneer and the improvement was huge and was wondering if tvs benefit in a similar way?

(quick update-i just tested the voltage between pin 6 and 5(gnd) on the FBT and got 136.3 volts so i assume this is fine?)
Attached Images
File Type: jpg IMG_20151008_113314_154.jpg (142.2 KB, 28 views)
File Type: jpg IMG_20151008_113259_127.jpg (112.6 KB, 28 views)
File Type: jpg IMG_20151008_112953_859.jpg (50.6 KB, 19 views)

Last edited by StarquestMan; 10-20-2015 at 02:47 AM.
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  #8  
Old 10-20-2015, 10:09 AM
zeno zeno is offline
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Pix has bending so try C903 first.
Then try turning the briteness all the way down & see
if the 135 V goes up.
BTW do you have a variac ??
I would not recap this set or most modern solid state sets.
Costs add up & things often go wrong. Just change the known
trouble makers.

73 Zeno
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  #9  
Old 10-20-2015, 02:29 PM
StarquestMan StarquestMan is offline
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ok i just checked the voltage with out replacing any caps just out of curiosity. the voltage with the brightness control all the way down was 136.5 and all the way up was 136.1. i do not have a variac or an isolation transformer for that matter (i learned the hard way what a "hot chassis" on my other Hitachi set, a CT-19A3, after nuking the bridge rectifier and nearly blowing up my old heathkit scope ). just out of curiosity what are some of the things that can go wrong when recapping a solid state set?
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  #10  
Old 10-23-2015, 03:43 PM
zeno zeno is offline
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OK the regulator is probably OK but the cap can still be bad allowing
garbage to get on the 135V line.
Turning brite down with a bad regulator will cause the 135 to go up
without the load of the CRT. Enuf & it will trigger shut-down.
Things that go wrong are self induced. Wrong value, backwards,
solder splashes etc. It happens to EVERYBODY sooner or later.
Also most small 'lytics have a zero failure rate on newer sets.
There are a few that are common to ALL sets to watch out for like
the ones I mentioned & the ones in the Vert output. Other than
that few & far between.......

73 Zeno



Quote:
Originally Posted by StarquestMan View Post
ok i just checked the voltage with out replacing any caps just out of curiosity. the voltage with the brightness control all the way down was 136.5 and all the way up was 136.1. i do not have a variac or an isolation transformer for that matter (i learned the hard way what a "hot chassis" on my other Hitachi set, a CT-19A3, after nuking the bridge rectifier and nearly blowing up my old heathkit scope ). just out of curiosity what are some of the things that can go wrong when recapping a solid state set?
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  #11  
Old 10-25-2015, 02:22 AM
StarquestMan StarquestMan is offline
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ok i should also mention that it has some slightly shaded vertical columns starting at the left and fading out about halfway across the screen (i think they are called "vertical bars"?) it kinda looks like looking strait down at a piece of corrugated roofing metal if this makes any sense. should i order any other caps for the set or is this just something to do with the shadow mask being wavy or some other issue? this issue doesn't really bother me much i just thought i would mention it in case it was an indication of another cap failing or was easy to fix anyway.
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  #12  
Old 10-25-2015, 11:03 AM
zeno zeno is offline
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Usually called jail bars. Almost always C701. This is
a common fail on all brands. Use a 450V replacement.
Causes a lot of minor symptoms also.
If you look at the 200V line with a scope you will see them.

73 Zeno

Quote:
Originally Posted by StarquestMan View Post
ok i should also mention that it has some slightly shaded vertical columns starting at the left and fading out about halfway across the screen (i think they are called "vertical bars"?) it kinda looks like looking strait down at a piece of corrugated roofing metal if this makes any sense. should i order any other caps for the set or is this just something to do with the shadow mask being wavy or some other issue? this issue doesn't really bother me much i just thought i would mention it in case it was an indication of another cap failing or was easy to fix anyway.
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  #13  
Old 02-25-2016, 05:35 AM
StarquestMan StarquestMan is offline
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sorry to resurrect an old thread. i got busy and haven't worked on the set for a while and have just recently replaced the 4 caps mentioned earlier which were c701, c903, c904, plus c716 since its esr was somewhat high and it looked like it leaked. it was late when i was changing the caps out and on the last cap i did (c701) i was so focused on making nice solder connections that i put it in backwards after it failed the smoke test and i replaced the fuse for the deflection circuit and corrected the um.... error, the set is working about as well as it was before. the cap that was put in backwards was warm right afterwards so i watched a movie to see if maybe the cap would reform and the picture would improve but it didn't. i even swapped in another capacitor but no luck. after blindly checking other caps i checked the windings on the horizontal output transformer with my esr meter (t701) and noticed something strange(assuming that this is a regular transformer not some sort of coil or autotransformer or something). one side (secondary?) seemed normal to me (3 ohms) but the other side (primary?) was open so i tested from one of the taps on the open side to the each tap on the other winding and got 64 and 72 ohms respectively. but from the other tap (connected to the collector of Q701) doesn't show any connection to anything. could that be the issue? would the set even work and produce a picture if that winding was open? or do i just not even have a clue what i am talking about here lol

edit: i started wondering about the results i got using an esr meter so i grabbed my DMM and tested the windings and have about 39 ohms on the side with the transistor (i called it the primary? and it tested open) and .8 ohms on the side that my esr originally showed as 3 ohms and there is no short across the two. from my understanding an esr meter is an ac ohmmeter and a DMM uses dc? im guessing i should just ignore the results from using an esr meter then?

Last edited by StarquestMan; 02-25-2016 at 06:00 AM.
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