Bad TV tuner. Repair or replace ?

[Dannyx]

Good day folks. It's been a while since I've actually had to do any TVs over at this new shop and I must admit I'm a bit rusty and need some help. Here goes:

Someone brought in a little piece of junk Sony knock-off portable TV saying it no longer tunes any channels. Fair enough, I warned the chap it's not going to be worth repairing it, but he insisted I have a look at it, so here's what I found:

Initially, a 5v buck regulator IC was blown (an LM2596), causing it to output 10v instead of 5v. That's been taken care of, but I believe it killed the tuner IC, since its maximum VCC is 5v and it took 10v like a trooper

I then popped the metal lid off the tuner and was greeted with the green sh!t you see in the first picture. I thought it's corrosion, but it's actually that green UV gel stuff they use to seal components on boards (Louis Rossmann actually calls it something but I forgot what it is) and due to the high heat generated by the chip, this thing turned solid and crumbly. I removed the green stuff and cleaned the area as best as I could with some q-tips and alcohol. I also noticed the metal can of the tuner got rather hot when the TV is on and it's apparently coming from this chip (the TDA6500TT). Spritzed some alcohol on it and sure enough, the puddle evaporates in the middle, leaving a round "hole" in the very middle of the liquid, which I believe is not OK and it's overheating. There's another chip there, a TDA 9886 which could've suffered the same fate, since they're in parallel.

It's also here that I realized that I don't know sh!t about TV tuners, the components inside of them and how they work and it would be an opportunity to learn...the datasheets for these ICs went a bit over my head, as beyond checking their VCC input, I'm not familiar with any of that stuff...frequencies and graphs and stuff.....:|

I also lack a scope, so the world of tuners is a pretty cruel one to be in at this point There's so much stuff to go over and I'd need a lecture on TV tuner basics and what to look out for when troubleshooting. Do you usually replace the whole can or do you dig inside and do component-level repairs ? What are the most common faults...stuff like that. It's probably trash anyway, but still....cheers and thanks.

[Andrew F. Ali]

Re: Bad TV tuner. Repair or replace ?

Repairing TV Tuners are a real pain, even for the experienced Tech. I would recommend setting up a TV Tuner separately. Once you can determine the AGC, VCC and IF OUT points. BTW you do have voltage at these points from the Mobo?

[R_J]

Re: Bad TV tuner. Repair or replace ?

One thing I will say right off the top is, do not atempt to straighten or move any of those wire coils, That is how the tuner is fine tuned, they look like a mess but thats how it works at those high frequencies

Check if you have VT on pin 15 of the tda6500, it should change between 1-33 volts depending on the channel, as you change channels the voltage should change, if it does, the ic might still be ok.
The tda6500 does the channel selection and outouts an I.F. signal, The TDA9885 takes the I.F. signal and demodulates it give you the audio and video signals. Can you recieve anything at all ? even noise (snow)?
Post the numbers from the tuner, it may be available as a complete module.

[Andrew F. Ali]

Re: Bad TV tuner. Repair or replace ?

One thing I will say right off the top is, do not atempt to straighten or move any of those wire coils, That is how the tuner is fine tuned, they look like a mess but thats how it works at those high frequencies

Correct.

[RJARRRPCGP]

Re: Bad TV tuner. Repair or replace ?

I then popped the metal lid off the tuner and was greeted with the green sh!t you see in the first picture.

Reminds me of toothpaste, LOL

[Dannyx]

Re: Bad TV tuner. Repair or replace ?

One thing I will say right off the top is, do not atempt to straighten or move any of those wire coils

Yes, that is one thing I was familiar with, so I didn't do that. I knew they were like that for a reason.

The part number is on the lid here, but couldn't find anything on it.
No signal whatsoever - blank screen all throughout the search process, even with the antenna cable from the wall so to say (it's got its own aerial but I don't expect that to tune anything). And yes, my co-worker was able to tune an analog TV on that cable, so there still is ATV on it and should work...I though that was the reason all along, but no.

[R_J]

Re: Bad TV tuner. Repair or replace ?

I looked up the board number and found pictures with the tuner Pt# JS-6B2/121
https://www.aliexpress.com/item/NEW-...585127520.html

[Dannyx]

Re: Bad TV tuner. Repair or replace ?

Interesting. Must've missed that one.

[Dannyx]

Re: Bad TV tuner. Repair or replace ?

Check if you have VT on pin 15 of the tda6500, it should change between 1-33 volts depending on the channel, as you change channels the voltage should change, if it does, the ic might still be ok.
The tda6500 does the channel selection and outouts an I.F. signal, The TDA9885 takes the I.F. signal and demodulates it give you the audio and video signals. Can you recieve anything at all ? even noise (snow)?
Post the numbers from the tuner, it may be available as a complete module.

Ja, see that's what I was talking about: learning about how these things work and their internal organs

[Dannyx]

Re: Bad TV tuner. Repair or replace ?

Also, when I measure that VT pin while changing channels, should this be with the antenna lead plugged in, or it doesn't matter ?

Another question: do these TV tuner cans share the same pinout generally ? What makes them different to one another ? I was thinking about all those leads coming out of the can...I can speculate what a few of them are like VCC, SCA, SDL, video, audio, clock (?) but that's as far as my knowledge gets me.

EDIT: let me answer my own question. I was able to find THIS. If you look to the right, it brings up a datasheet which is mostly in chinese but includes a pinout of the damn thing nonetheless. Turns out I was right about some of those pins.

[R_J]

Re: Bad TV tuner. Repair or replace ?

The TV voltage (tuning voltage) will change depending on the channel and no input is necessary. The voltage will change from 0-32 v as it goes through the channels of the band that is selected . This is only a monitoring point for the ic and may or may not go to a module pin.
I found this site http://www.radioscanner.ru/forum/topic23937-19.html
They seem to have the pinouts
The ic has an internal charge pump to develope the 32v VT

[Dannyx]

Re: Bad TV tuner. Repair or replace ?

32 v...must be a boost converter in the there somewhere then, since the input is a 12v wall-wart.

[Dannyx]

Re: Bad TV tuner. Repair or replace ?

This little TV is still being worked on by my colleague (though "slave-driver" would be more appropriate term to describe this fella >_>) who refuses to accept my idea that the IC should not get that hot and he's dauntlessly pushing on doing....whatever he's trying to do, so I'll keep you folks posted on how it all ends. This is gonna be good

[sintv]

Re: Bad TV tuner. Repair or replace ?

Sorry but I dont understand why youd want to repair an old portable set. Sell him a freeview box and save your energy for a more profitable repair

[Dannyx]

Re: Bad TV tuner. Repair or replace ?

My thoughts exactly: had it been only the power issue I described, then yes, it would've been worth it because it was cheap and relatively easy to solve, but once we start going any deeper, it's indeed a waste of time.

Like I said: I'm not the one working on it at the moment, since of course I would've scrapped it and not even bother, but the old geezer of a colleague of mine likes pursuing these avenues which are completely pointless by wasting time with junk like this which is a waste of time (and money !). Telling him something is trash and is not worth or cannot be fixed is almost like a curse word to him and it sends him into a veritable feat of rage which you, the unfortunate soul who dared "insult" his repair skills, has to fight back....oh boy I could write pages on this guy, but that's enough digressing for today. Like I said: really curious to see how it all ends

[Dannyx]

Re: Bad TV tuner. Repair or replace ?

Ok guys, here's the situation: apparently my "buddy" here did replace the IC eventually (the large one - can't remember what it was) but still no channels, so I was right not to bother....call me a slacker, I know
Speaking of which: does moving those coils around affect reception entirely or just some of the channels ?

[R_J]

Re: Bad TV tuner. Repair or replace ?

Yes moving the coils will effect the channels, the coils are adjusted by moving the coil windings, It looks like there is a coil for adjusting the i.f. frequency of each band and one is for an i.f. filter
So it will likely still receive channels.

[Dannyx]

Re: Bad TV tuner. Repair or replace ?

He managed to fix the thing apparently. He replaced the small chip in the tuner from what I recall, but he also messed around with the EEPROM chip and he claims THAT'S what actually got it going, which I disagree with - it was that IC that solved it...