Question for any TV tech out there

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geewiz
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Question for any TV tech out there

Post by geewiz » Thu Apr 03, 2003 9:23 am

Okay, here's the deal: some time ago an old (10yr) Toshiba started with the clicking sounds when turned on. Eventualy failed to power up (HOT failure??). Repair center took a month with it, and when it was returned I noticed set appeared to have a fine tuning problem (not a pre-existing condition). There was "noise" in pic even with no signal (RF or otherwise) plugged into set; not AC related. Tech supposedly tracked problem to a tuner module (which was no longer available; was told Toshiba NLA their components after 5yrs). I had to find the part myself (they couldn't), and after a hunt, found it for little under $100(normal pricing would have been less I think). Tech replaced part and now tells me that was not the problem; fine-tuning issue still exists. <p>Anyone has any opinions as to what the problem is/could be? Also, note that as far as I'm concerned, this tech will not get any more $ from me. Am I right? TIA

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haklesup
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Re: Question for any TV tech out there

Post by haklesup » Thu Apr 03, 2003 12:17 pm

Sounds like a ground loop picking up noise from a circuit inside the set. There are many sources of noise in a TV. Look for unattached shield or ground wires. Wires (especially to ground) that were added by the tech at the time of repair. Broken or cold solder connections anywhere but especially ground or supply connections. Also look for dried out or buldging (or vented)electrolytic capacitors. Inspect any connectors that go board to board or any contact that may carry lots of current. Look for bad crimp or anything that would increase the resistance of an otherwise low R wire.<p>Since the noise is present with no RF signal, (unplug the tuner RF cable internally)look further back in the circuit like the Vertical or Horizontal scan circuits rather than the tuner. By measuring the frequency of the noise, you may ba able to guess at the source.<p>You must love that TV since repair costs approach replacement cost for most TVs 25" or less. IF it is due to a bad contact causing a ground loop, the tech may have caused it but if it is a bad cap, it's probably just a coincidence.

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Edd
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Re: Question for any TV tech out there

Post by Edd » Thu Apr 03, 2003 4:16 pm

geewiz….and that’s not geewhiz ?
On your Toshiba, did the set go directly to service or did you do any looking at the chassis yourself? Also how about a further refinement of the description of the effect on the picture of the “fine-tuning” problem. In respect to evaluation of the picture, how about hooking the set up to a VCR as your RF signal source and monitor on the TV on Chan 3or 4…whichever. Use a good commercial prerecorded tape so as to obtain a quality picture reference. Typically the VCR’s modulator will be hitting your sets tuner with ~1000uv of signal level which should make a slick picture on the TV. Now evaluate…if the picture is not slick, would there be a uniform coarse grainy picture ?
If less severe than that , would you describe it as a less severe, slight background agitation effect ? If the latter is the situation, its time to get into the menu of the set’s adjustments and see if the sharpness adjustment has been skewed off towards the max definition end of its range.Usually its at center range or even to the lower def side unless you have one good quality of signal for sig source e.g. digital cable or satellite that is able to produce such a pristine signal quality to permit the setting of that control to its max sharpness end. Usually most antenna signals or conventional cable (with repeated line amp introduced noise) will have a somewhat degraded signal.
Without your feed back available in the interim you might just take that VCR and feed its raw Video and Audio into the corresponding inputs on the back of the TV and then be able to get a good picture on the set again..Plus that definitely zeroes in on your Toshiba’s RF or IF or Saw filter section as being suspect or the simplest would just be a delayed AGC problem.
Definitely need to know the model number from the back of the set. Expect 2 alphabetical characters followed by 4 digits the first 2 being relevant to Ur sets screen size. Also there is a chassis number ….Usually TACxxxx with the #’s being almost the same as the model #.If you will supply that by Sat I’ll see specifically what that set uses in the d-AGC circuitry.<p>73's de Edd
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geewiz
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Re: Question for any TV tech out there

Post by geewiz » Fri Apr 04, 2003 9:59 am

Thanks for the replies, guys. The Toshiba in question is a CX27D60. Never tried hooking up a VCR, but symptoms appeared with no signal, and RF signal from cable, and a composite signal from dvd player. The best I can describe it is picture looks like it's mistuned. Recall older TVs that had the tuning ring around the channel selector. Well, that's what I need; a slight adjustment to fine tune pic. Note that noise apparent even shows up on blank muted screen, with nuthin' connected other than AC. <p>I am going to print your responses to show the tech working on the unit. I'd given him until this weekend; maybe your posts will point him in the right direction

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Edd
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Re: Question for any TV tech out there

Post by Edd » Fri Apr 04, 2003 1:21 pm

gewiz:<p>Your initial info didn’t specify that U had a Video disc player…..now if you had that going into the RCA jacks on the back input jack panel of the Tosh, that picture should be PERFECT as you’re bypassing all RF processing circuitry and going directly into the video section of the Tosh..(Unless you happen to have one of the few players that dump out the signal as a ch 3 or 4 RF signal…in that case different story ..as you are still going thru RF and IF circuitry). The only common thing that comes to mind, in the case that the picture produced in that direct video input mode of operation is squirrelly, is the ~250v B+ that feeds the final stages of the video amp could be receiving contamination from spikes from the hoz circuit. This supply is sweep derived from a winding from the flyback transformer and after rectification is then filtered by an ~5-10 ufd electrolytic of all the hoz hash. The 15khz freq of operation tends to take a toll on these filters and the video gets contaminated and even your overall brite is affected. At their last stages of failure even blanking is affected and you are able to see a non uniformity of brightness across the screen from left to right. Usually that cap is right near the flyback but on some sets there is a supplemental unit at the kine driver board at the kine.
As per the reference to the “ fine tuning” …..your set uses a synthesized PLL digital style of tuner and is rock solid……and if I remember right being a 60 series that chassis should have one big jack panel on the rear and even a Comb filter in its design…..basically all of the bells and whistles…..and oh yes steeee-ro sound.
You also might ask the servicer specifically what all parts were changed in the repair work that was done….as if the problem was DOA typically that would have been a power supply or sweep section (or both) type of repair that typically, normally wouldn’t be associated with the effect you are now experiencing……On the bright side look at it this way …..you now have a spare good tuner and its even NLA !.
Will pull the roadmap on that chassis this weekend for further research if it doesn’t rain.
The last thing of course in analysis would to be able to see that picture……aptly covered by the old adage…a picture is worth a thousand words !<p>
73's de Edd
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geewiz
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Re: Question for any TV tech out there

Post by geewiz » Sat Apr 05, 2003 12:11 pm

I've forwared your responses to the tech and haven't heard back anything (usually I have to contact him; he never contacts me!). And, yup, image show smae problem via composite input. I should also have mentioned that the unit lived in a heavy smoke and dusty environment.

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dacflyer
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Re: Question for any TV tech out there

Post by dacflyer » Sat Apr 05, 2003 10:31 pm

is it possible he used the wrong HOT transistor? did he reinstall any ferrite beads,,,some hots use them...also the tuner in question could have been sent off to PTS and tested or repaired for bout 75.00 , and if he was a real tech..he could have substituted the tuner with a if generator..
anyway... hope you get it fixed !

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