Sony - KV14T1U - CRT

[tmcw]

Was given one of these today, was told it was working well up until a few days ago when a pop was heard, and the TV switched off, and wouldn't come back on again.

Not sure where to start with it...

When I switch it on, I can hear what I presume is the degausser. Fuses in the plug and on the board are both ok. I noticed that quite a few of the solder joints on the solder-side were looking a bit skimpy on the solder, so I reflowed and added another bit to get a nice mound on them (picture is from before I did this).

Nothing visibly burnt or fried (there is solder point near where "Primary Power Supply" is written that looked burnt, but I believe it's just excess flux).

I have a schematic, after downloading quite a few, I found it with a search of a similar set, subbing the T for an M and searching for a kv-14M1K (as I saw in a 21" version of this series had both M and T in the same document). But not sure where to begin probing to narrow down what might be at fault.

Chassis seems to be a BE4. I've attached a photos of both sides of the chassis. Has anyone worked on this chassis before, and where is the best place to start and approach this safely?

EDIT: Found this page http://www.eserviceinfo.com/repair_t...earch_rt=KV14T which says that the chassis is a BE4, and after looking at the schematic document closer, I can see BE4 mentioned on the top of a few of the pages.

[budm]

Re: Sony - KV14T1U - CRT

More service info here:
http://elektrotanya.com/?q=showresul...at2=schematics

[tmcw]

Re: Sony - KV14T1U - CRT

Thanks for the link, the document is better than the one I'd gotten.

So I suppose I should start with the power input area, but unsure as to how to properly (and safely) measure the voltages in this area, so have a few questions, and have attached that portion of the schematics.

1. When measuring voltages, are the voltages in the area after "T602 SRT" AC volatges? (Or are these now DC since they come after the "AC RECT" D610?)

2. Where do I measure between? For instance, on the point (11) on the T602 SRT where it says it should be +118V-RECT, I put one lead on point 11, but where do I put the other lead?

3. Similarly, if I'm measuring voltages between the "T602 SRT" and the AC in, where should I put the black lead?

[budm]

Re: Sony - KV14T1U - CRT

OK, this is switching power supply, it does not run at 50 0r 60Hz, the transformer is being fed by AC voltage generated by the U801, the frequency is about 70~100KHz, your meter will not be able to read AC at that frequency, you will need scope.
The most important thing is that, any thing in the left side of the transformer are part of the AC primary circuit, so do not TOUCH anything with your body, the ground of the primary is not tied to ground of the secondary side of the transformer.
The diagram is basic block diagram drawing, you should look at the detail schematic instead, but you can still check the DC out put of the rectifier diode that is connected to pin 11 of the transformer, since you are checking the secondary side of the circuit, you can put you black probe of your meter to any metal part of the chassis which is tied to the secondary ground.
I am not sure how much experience you have working with CRT, the CRT can hold 30KV for days, so be careful, I would plug this unit into isolation transformer and GFI outlet for safety while you are working on it.

[tmcw]

Re: Sony - KV14T1U - CRT

Thanks for the advice. I have a scope, so I will get it out, and have it on hand to try and test some voltages on the primary side.

I did test at point 11, but am only getting something like 18V, IIRC.

I've worked mainly on LCD panels before, not so much CRTs, but am mega-careful. I've mainly had obvious cap, and sometimes diode problems, so have tested a few diodes out of circuit in that area, and they've tested ok.

On that +118V line, I took off the bridge rectifier (D610), and it's ok. The next component R615, I tried measuring it's resistance, but it's reading open. But I notice that it's symbol isn't a usual resistor like on other places, the symbol looks half like a resistor, and half like an AC symbol. Can someone enlighten me on this? I've attached part of that area including the resistor.

[budm]

Re: Sony - KV14T1U - CRT

Do not hook up your scope to the primary side of the circuits, you will blow the scope and the circuits, you have to use isolation transformer on the monitor since the scope ground is tied to safety ground.
That is the 0.47 Ohm fusible flame-proof resistor for the B+, if that is open, then the IC may be shorted or the secondary side of the transformer is drawing too much current.
Just Google "fusible resistor"
I.E.:
http://www.te.com/catalog/feat/en/s/26890

You should build one of these, it will help you to find out if you still have shorted circuits after replacing the parts or not.
https://www.badcaps.net/forum/showpo...3&postcount=12
It basically put 120V lamp around 75~100W in series with the unit under test, if the lamp stays brightly lit then you still have shorted circuits, if the lamp lights up bright then dim down, it means you are OK.
http://s807.photobucket.com/albums/yy352/budm/Tools/

[tmcw]

Re: Sony - KV14T1U - CRT

Thanks, didn't use the scope because when I switched it on, I found that the display was vertically squished, but it might be an easy fix (haven't done it yet, thanks to this page I saw http://www.home.agilent.com/owc_disc...art=0&tstart=0 I guess we can forgive failing caps in equipment of this vintage.

Anyway, in the meantime I got a newer Sony TV (similar size, but a couple of years newer), but is pretty beat up, case and some parts of the boards inside are a bit broken, but a lot of the parts on the power supply area look like they're the same if not similar.

It has the same 0.47 ohm fusible resistor, and it behaves as I'd expect it to under test, so the one in the first set was likely damaged. If that is the case, what tests should I carry out before switching it in? Test the T602 transformer between for instance point 1 and 3, 11 and 12 in the attached schematic in post #3 above? What values should I expect? Will I need to remove the transformer? Anything else I should do? (or not do?) It might be a while before I can get the parts to built a test apparatus like you posted above budm.

[budm]

Re: Sony - KV14T1U - CRT

Check the resistance reading between pin 1 of the transformer and ground of the primary (negative leg of the main DC filter in the primary circuits).
You should for sure build or put the 120V lamp in series with this TV.