Author Topic: Toshiba 40LB702B No sound  (Read 343 times)

0 Members and 1 Guest are viewing this topic.

Davy

  • Hero Member
  • *****
  • Posts: 202
Toshiba 40LB702B No sound
« on: October 08, 2017,08:29:02 »
I suspect bad connections on the underside on the AF output chip.

Any repair tips on how to resolder?  This telly uses the Vestel 17MB65S-3 main board, all other functions are OK.

Dave

Mulja tv repair portal

Toshiba 40LB702B No sound
« on: October 08, 2017,08:29:02 »

kennyc

  • Sr. Member
  • ****
  • Posts: 152
Re: Toshiba 40LB702B No sound
« Reply #1 on: October 08, 2017,08:49:15 »
Hi Davy ,have never had any success fixing a board apart from taking a chance on replacing with one from Ebay . Usual fault is the sound goes of after a couple of hours and you turn it off and on and its OK again.  I usually tell customer to buy a cheap soundbar at Tesco for 25 and just charge them for a call out and advice if you can get away with it. Sometimes people will want you to go and buy one and install it

Davy

  • Hero Member
  • *****
  • Posts: 202
Re: Toshiba 40LB702B No sound
« Reply #2 on: October 08, 2017,10:42:26 »
Thanks kennyc, you are right.

I tried pressing darn hard on the chip  - no joy, I checked the four ceramic caps that give problems and they are OK. The supply voltage appears to be alright, so dunno guess it could be further back down stream.

Yep, me thinks a new board is required, or a 'goodun' at least,  gawd, bring back the ol' heavies, these modern things sound like pip and squeak - definitely not hi-fi.... lol, the sounds that clear you can hear the distortion.

Keep soldering, Dave

Mulja tv repair portal

Re: Toshiba 40LB702B No sound
« Reply #2 on: October 08, 2017,10:42:26 »

Turnip

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 3217
    • Email
Re: Toshiba 40LB702B No sound
« Reply #3 on: October 08, 2017,11:01:50 »
Hi Dave,

Had a few with either no sound or sound going off after a while. It was always those little ceramic caps - Never tested 'em just replaced with considerable difficulty as they tend to fly about a bit as it's hard to hold 'em down to solder.

Got a bag of 100 as I lose three for every one I fit, and can never find them again - Chris.

Davy

  • Hero Member
  • *****
  • Posts: 202
Re: Toshiba 40LB702B No sound
« Reply #4 on: October 08, 2017,14:21:40 »
There's four of em in a line, I guess they're the ones, I did test them for being s/c only, since the 12V line is OK I assumed they was OK.

I do have smds, do you know what they are off hand, 10n perhaps?  When I get time I'll pull em and try some in, I'll measure them on my LCR meter.

This one is stone dead on audio.... headphone socket included, there is a mod going about sticking a small heat sink on the NPT8030 chippy to help save the solder from heat damage.

These mod con tellies make there gramophones with a steel needle connected  to a soup can sound like hi-fi.

Dave

Turnip

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 3217
    • Email
Re: Toshiba 40LB702B No sound
« Reply #5 on: October 09, 2017,13:05:48 »
Hi Dave,

They're 0.8 Mfd 6.3v - Though seems value can vary a bit making little difference.

Wouldn't mind but they're horribly small to replace without print damage, and most of 'em get away never to be found again.

Best of luck - Chris.

Mulja tv repair portal

Re: Toshiba 40LB702B No sound
« Reply #5 on: October 09, 2017,13:05:48 »

Davy

  • Hero Member
  • *****
  • Posts: 202
Re: Toshiba 40LB702B No sound
« Reply #6 on: October 11, 2017,15:17:04 »
Too right they are horribly small.... yikes 0.8mfd, geesh that's 1u innit.... now 0.8pF I'd be understanding lol.

Well, the chap went out and bought a new telly, when time permits I'll have a play so if ya' see the moon with two faces 'giffus a wave'.

I did get the circuit but it doesn't show them on!!!! I can see them on the layout but certainly not on the diagram, only shows the basic gubbins. The NTP-8030 capable of generating 30 watts per channel and will work from 7 to 28V... me thinks it need a liquid nitrogen supply, PCL84 bless em' they'd work, work and work.

Dave

Turnip

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 3217
    • Email
Re: Toshiba 40LB702B No sound
« Reply #7 on: October 12, 2017,11:28:04 »
Hi Dave,

Attached a diagram of sorts. You'll feel really great if you get 'em all in straight and the sound booms out in a true Vestel manner. Noticed in other Vestel boards they seem to use discrete audio chips around 3mm square using the board as a heat sink. Haven't met a duff one yet, and as they have underside connections I don't want to.
Wasn't the PCL84 a CDA in certain early hybrids ? Preferred the PCL83 as it went all Black inside and burned up the volume control - Bit of an earner.
Out of interest have an ancient French radio in to sort - Made in the 50's by a man and a dog in a shed - (Vinix) Was checking valves as you do and came up with the ECLL80 - Never met one but really impressed as the triode and one of the pentodes share the same control grid due to a lack of pins. Also met a push-pull audio amplifier using a couple of ECL80s with all the cathodes connected together - Nifty - Chris.

Davy

  • Hero Member
  • *****
  • Posts: 202
Re: Toshiba 40LB702B No sound
« Reply #8 on: October 13, 2017,20:22:13 »
Uh, I thought they were C80, 81, 82 and 83 15nF, not the ones that you pointed out.... see this video
https://www.youtube.com/watch?v=JV-v9CfH7ow, thanks for the link, I've made a note of those 1uf caps.  Not exactly the same model as in the video but sure does look the same board.

There is sound at the headphone output but it isn't what I would call loud, I'm wondering if it's  the muting contact on the socket, I'll have a shufty when I get time.

One common trick to get the sound back is to enter into the service menu and do a factory reset, I understand Toshy issued a firmware update on a USB stick for this.... I did try a  'Search for update' but non was found, still no sound.

Dave

Turnip

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 3217
    • Email
Re: Toshiba 40LB702B No sound
« Reply #9 on: October 14, 2017,12:35:03 »
Hi Davy,

Can't say,

Only that I replaced the caps in the picture and sound returned, and they were 0.8Mfd 6.3v.

Horrible job but each set had sound of a tinny sort.

Had a 48 inch Vestel Celcus in the other day and it uses the same speakers as in small screen Vestel sets, Realise it's budget but surely they could have squeezed in a woofer for a couple of quid more.

New budget sets tend to use Chinese boards, Vestel seemingly too expensive, and we know what they're like with 'End Of The Road Guarantees' and later Eeprom issues -  Chris.

 

Powered by EzPortal