Hitachi LCD low squeal from speakers

[DoctorWedgeworth]

I had one of these that wouldn't turn on, turned out to be 5 blown caps on the PSU. I replaced them, and it works, but now when it's on a no input screen, or another silent screen, it emits a low volume squeal. It's possible it does this all the time, but it's not noticeable when there's sound playing.

It goes off if I hit mute, and I never saw this TV on before I replaced the caps. Someone suggested I might have shorted it slightly when replacing a cap, and the speaker is transmitting this as noise. Is that possible?

It's not a big deal and I don't want to have to spend anything to fix it (except maybe a couple of quid on components), but if it's an easy fix I'm all for opening it up again.

[multimeter]

Re: Hitachi LCD low squeal from speakers

check power board grounding points,could be picking up oscillations from smps transformer,did you use decent branded caps to replace?,i.e checking the esr,ripple is higher or equal?rubycon,panasonic?

[DoctorWedgeworth]

Re: Hitachi LCD low squeal from speakers

I used the cheapest caps I could find (from eBay) and only thought to check the numbers not the brand. I know that might sound like sacrilege here but it was before I discovered this forum.

[multimeter]

Re: Hitachi LCD low squeal from speakers

you need to check what the blown caps caps were,the impedence,the ripple current,the voltage,and stay the same or EXCEED the specs,if you used caps that were a higher impedence (esr) the power supply will be struggling to push power through to its respective rails,in your case the rail that supplys power to the audio side of the mainboard,eventually the psu will fail ,if the caps are not correct,then this possibly could alter the output rail voltage,as a rule,i always use panasonic fm in every power supply i repair,and never had any problems whatsover,at the moment im looking for a scope to check power supplys,to make sure there is minimum output ripple from the rails,at the moment i use a dmm to make sure the output voltages are within spec of what they should be,if you have one then check voltages are correct,a low voltage somewhere could underpower the amp circuit and cause speaker noise.

[DoctorWedgeworth]

Re: Hitachi LCD low squeal from speakers

Thanks for the advice. I threw the old capacitors away, only made a note of the u and the voltage. Guess this is a learning curve

I might see if I can find an instruction manual for this TV online to find out what they should be and/or what the voltages should be. I do have a DMM, although I'm not sure how good it is.

[multimeter]

Re: Hitachi LCD low squeal from speakers

try here http://elektrotanya.com/

[multimeter]

Re: Hitachi LCD low squeal from speakers

trouble is if you do find a schematic diagram,it wont state the brand and series of the capacitor,only the uf and voltage,if you knew the old brand and series,you can look up the datasheet ,and compare results

[tom66]

Re: Hitachi LCD low squeal from speakers

Is the chassis made by Vestel? I have had several Vestel TVs using the same particular audio circuit, and they all make a low squeal - they are rubbish!

[DoctorWedgeworth]

Re: Hitachi LCD low squeal from speakers

It's a Hitachi 32LD6600B. There's no mention of Vestel on the label.

You seem to follow me around telling me my TVs are rubbish

[tom66]

Re: Hitachi LCD low squeal from speakers

It's a Hitachi 32LD6600B. There's no mention of Vestel on the label.

You seem to follow me around telling me my TVs are rubbish

Yours is a Vestel. This is the audio board. http://flattvparts.co.uk/bmz_cache/5...ge.400x305.jpg

It *may* help to replace those capacitors on it but I couldn't guarantee it.

Sorry, but I have opened up too many and have too many opinions . When you repair a Sharp, Sony, Panasonic or Toshiba you start seeing quality. (Except the newer Sharp and Toshiba TVs which are just Vestels!)

I will say this simply: Vestel the worst, most unreliable TVs ever. They are built using bottom of the barrel components and they are very poorly laid out. And now, you see brands like "Finlux" who are just rebadging Vestel TVs. No "happy Finnish" when it dies in 14 months time.

[DoctorWedgeworth]

Re: Hitachi LCD low squeal from speakers

Do you think it's worth bothering? If the TV was likely doing it from stock it doesn't need to get better.

I was going to keep this for myself but I might just sell it on until I get my hands on a Sony or something.

[tom66]

Re: Hitachi LCD low squeal from speakers

Do you think it's worth bothering? If the TV was likely doing it from stock it doesn't need to get better.

As you said you only notice it on no input screens so I can't see it being an issue.

I was going to keep this for myself but I might just sell it on until I get my hands on a Sony or something.

Samsung and LG are okay too, once fixed. Better than Vestel. Fixed 4 Samsung LCDs + 1 Samsung plasma and 2 LG LCDs + 2 LG plasmas my self. Usually quite easy to fix once you get the meter out and test things.

[DoctorWedgeworth]

Re: Hitachi LCD low squeal from speakers

Nah it's not just input screens, it's any silence is replaced by it. It's actually constant and noticeable between gaps in sound (you learn they're quite frequent!).

Can I use my basic DMM to figure out which capacitor it might be?

[tom66]

Re: Hitachi LCD low squeal from speakers

Nah it's not just input screens, it's any silence is replaced by it. It's actually constant and noticeable between gaps in sound (you learn they're quite frequent!).

Can I use my basic DMM to figure out which capacitor it might be?

No, for this kind of problem, you need a scope to trace the noise source.

[DoctorWedgeworth]

Re: Hitachi LCD low squeal from speakers

What's a scope? I tried searching for it on Google and products on Amazon but I'm coming short. I saw an article about removing capacitors then connecting them to a multimeter, the resistance should start at zero and move to infinity. Will that not work here?

For testing the voltage going to the speakers will I need to find the instruction manual?

[tom66]

Re: Hitachi LCD low squeal from speakers

What's a scope? I tried searching for it on Google and products on Amazon but I'm coming short. I saw an article about removing capacitors then connecting them to a multimeter, the resistance should start at zero and move to infinity. Will that not work here?

For testing the voltage going to the speakers will I need to find the instruction manual?

Oscilloscope. Lets you view the voltage waveform with respect to time. They run from £40 to £140,000.

The Rigol DS1052E is an ideal scope, starting new from £250. You can also get a cheap analog scope (fine for most tasks) for less than £100 in most cases.

[multimeter]

Re: Hitachi LCD low squeal from speakers

What's a scope? I tried searching for it on Google and products on Amazon but I'm coming short. I saw an article about removing capacitors then connecting them to a multimeter, the resistance should start at zero and move to infinity. Will that not work here?

For testing the voltage going to the speakers will I need to find the instruction manual?

a scope is an "oscilloscope" used for measuring waveforms,voltage,ripple current etc.

you can use a meter to give an indication that the cap is charging and discharging,an analog meter is better for this,normally called a "kick test",to test the condition of a cap ,you need an ESR meter,it will give you the impedence of the cap,the readings need to be in spec with reference to a datasheet,some also give the uf of the cap,and so will some digital/analog meters

i suggest you check first, the output voltages (dc) against there pcb marking,at least it will tell if the psu is outputting what it should be.

mark each connector down ,with the pin number ,and its voltage marking,and its actual reading that you measure.


example:

c100 pin 1 voltage 12v measured 12.68v
pin2 voltage 5v STB measured 5.33v
or

conn 26 etc etc