32" Goodmans TV

[tom66]

Re: 32" Goodmans TV

Okay, it's open...

5VSTBY is 5.04V
3.3VSTBY is 3.36V

Both are good.

Main PFC bus voltage still stuck at 328V, but it used to work on this.

The set is stuck in standby, but the main 5V line measures 1.8V...? Could be an issue.,

3.3VSTBY is getting 600mV dips on it when the LED flashes. (A whining sound is also briefly emitted during this time.) This downwards going pulse might be the reason the set is cycling, but what is causing it?

The LED flashes approximately three times a second and the 3.3VSTBY dips are in phase with it when it goes out...

Note that the TV is not being switched on at this time. This occurs as soon as it is plugged in.

[tom66]

Re: 32" Goodmans TV

I did more reading of the panel datasheet to try and get a better understanding of how the bugger works. I'm looking at the LVDS cable at the moment, I'll let you know how I get on. You had any luck with what you were trying?

Haven't opened it up yet... leaving that for tomorrow.

I also have been offered an Acoustic Solutions 32" TV. Made around the same time as the Goodmans. Has a problem: turns itself off after a few minutes. Could be bad caps. Who's betting it's using a 17MB22 chassis too?

Rather interestingly I caught eye on an Acoustic Solutions 32" with faulty sound. Of all companies to get sound right, it should be Acoustic Solutions... It sold for too much though.

I'm on the look out for a 42" Full HD TV. I got a 42" 720p from the local tip . Honestly, I don't know how much difference it will make at the distance TV is watched at, around 10 ft.

[dumpystig]

Re: 32" Goodmans TV

I did more reading of the panel datasheet to try and get a better understanding of how the bugger works. I'm looking at the LVDS cable at the moment, I'll let you know how I get on. You had any luck with what you were trying?

[tom66]

Re: 32" Goodmans TV

Yeah Snap! WTF? Been having a different prob the last 2 days - switch on, tries to power up, locks out with LED flashing for a couple of mins.

I now seriously believe it to be somewhere on the inverter/backlight stages.
In the LG Panel datasheet it shows the power sequence for the panel and the inverter/lamps but I don't have a 'scope so can't get very far with that. But also the inverter start voltage [PL003/1 > PL803/1] should be Min.3VDC - Typ.5VDC but most times my M/B is outputting around 2.9VDC and I reckon this is crucial. It could also be that there is an intermittent fault further along either on the inverters or the lamps. You any idea how to access the lamps?

You'd have to take apart the display entirely being careful not to damage the LCD panel. I've salvaged lamps from LCD TVs before.

I'm going to scope the standby PSU. Suspect bad caps.

[dumpystig]

Re: 32" Goodmans TV

Yeah Snap! WTF? Been having a different prob the last 2 days - switch on, tries to power up, locks out with LED flashing for a couple of mins.

I now seriously believe it to be somewhere on the inverter/backlight stages.
In the LG Panel datasheet it shows the power sequence for the panel and the inverter/lamps but I don't have a 'scope so can't get very far with that. But also the inverter start voltage [PL003/1 > PL803/1] should be Min.3VDC - Typ.5VDC but most times my M/B is outputting around 2.9VDC and I reckon this is crucial. It could also be that there is an intermittent fault further along either on the inverters or the lamps. You any idea how to access the lamps?

[tom66]

Re: 32" Goodmans TV

No....

It just died!

When turned on the standby LED blinks on and off.

Bad caps... I hope so this time.

I will also attempt to fix the PFC circuit.

[dumpystig]

Re: 32" Goodmans TV

I had various symptoms, from 2s-to-black/intermittent running/LED flashing (various rates)/not starting with HDMI connected. As I seemed to resolve one issue another arose, so I've been all over both the PSU and M/B, looking at the circuit diagrams and trying to rectify the relevant stages on each board. It's taken me absolutely ages over the past 3 weeks, done my head in at times, but I saw it as a challenge and was determined to fix the bastard.

I simply attached the heatsink with superglue; over the years I've found it to be very effective in all sorts of applications. The original T-Wing is only attached with adhesive anyway so I guessed I had nothing to lose - as it turns out it's working rather well in conjunction with the fan.

[tom66]

Re: 32" Goodmans TV

It seems to have been an issue on my board - as I mentioned in an earlier post it was reflowing SMD components around/underneath/adjacent to this chip that finally provided my fix.

Odd. What were the symptoms when your TV wasn't working?

Also, did you use thermal paste for the new heatsink?

[dumpystig]

Re: 32" Goodmans TV

It seems to have been an issue on my board - as I mentioned in an earlier post it was reflowing SMD components around/underneath/adjacent to this chip that finally provided my fix.

[dumpystig]

Re: 32" Goodmans TV

Pics attached:

[tom66]

Re: 32" Goodmans TV

IC400 is the VCTP Microcontroller on the M/B - it's near the centre of the board and has the semi-rigid heatsink attached that resembles a 3" long piece of black tape - does yours not have this? And the chip does get pretty hot, on mine anyway. I'll upload a pic shortly.

Yeah, I see it. Agreed, it gets hot, don't imagine it being a major issue though.

[dumpystig]

Re: 32" Goodmans TV

IC400 is the VCTP Microcontroller on the M/B - it's near the centre of the board and has the semi-rigid heatsink attached that resembles a 3" long piece of black tape - does yours not have this? And the chip does get pretty hot, on mine anyway. I'll upload a pic shortly.

[tom66]

Re: 32" Goodmans TV

Tom, is your set finally sorted now? Regarding the whining, try checking the inductor L817, that's where I was getting a lot of noise on my PSU; I rolled an A4 sheet of paper into a narrow cone and held it to my ear to help pinpoint the source on the board. I applied a couple of drops of superglue to the top of the copper winding and let it permeate and dry. Repeated this several times, allowing the glue to build up and encase the winding. Now it's almost silent.

It is working now and has worked for the past few days. I'll try and find the source of noise and try your glue trick - I've heard of it before.

My set has been running perfectly over the last three days and I've not had to replace any components. The main thing that worked for me was resoldering loads of joints, concentrating on those parts of the circuit that I deduced (hoped) to be the cause. I think the worse components I found were adjacent to or underneath IC400 on the M/B; it does get quite hot and that T-Wing 'heatsink' seems to me to be almost useless so I removed it and replaced with a small aluminium 'sink from a fubar router I have. I also modded the TV back casing and fitted a 50mm PC case fan directly above IC400 - the difference now in it's temp is amazing, getting nowhere near as hot as it did. The fan is powered from the 12V IDTV supply with a 3W resistor to lower the speed so it's inaudible when the set is on.

Did you suss that the M/B PROTECT_DETECT circuit does nothing regarding the PSU? It goes to PL803/5 and stops there - had me confused for a while as I was assuming maybe this was causing the fault.

I haven't had a good look at the board. What is IC400? Is it the SMPS PWM controller? It would be unusual for that to get hot unless it has a built in MOSFET.

Yeah, I eventually found out that the protection on the motherboard isn't used by the PSU. Although, it does go into the CPU. So it's possible that could cause the same symptoms. In my case, it was just the soft start FET Q837.

Anyway, after all the time I've spent on this and reading of many other faults I reckon these Vestel boards are a complete ballache because of dry joints. But at least I'm sorted now, so happy days.

Agreed. Cheap OEM'd junk...

[dumpystig]

Re: 32" Goodmans TV

Tom, is your set finally sorted now? Regarding the whining, try checking the inductor L817, that's where I was getting a lot of noise on my PSU; I rolled an A4 sheet of paper into a narrow cone and held it to my ear to help pinpoint the source on the board. I applied a couple of drops of superglue to the top of the copper winding and let it permeate and dry. Repeated this several times, allowing the glue to build up and encase the winding. Now it's almost silent.

My set has been running perfectly over the last three days and I've not had to replace any components. The main thing that worked for me was resoldering loads of joints, concentrating on those parts of the circuit that I deduced (hoped) to be the cause. I think the worse components I found were adjacent to or underneath IC400 on the M/B; it does get quite hot and that T-Wing 'heatsink' seems to me to be almost useless so I removed it and replaced with a small aluminium 'sink from a fubar router I have. I also modded the TV back casing and fitted a 50mm PC case fan directly above IC400 - the difference now in it's temp is amazing, getting nowhere near as hot as it did. The fan is powered from the 12V IDTV supply with a 3W resistor to lower the speed so it's inaudible when the set is on.

Did you suss that the M/B PROTECT_DETECT circuit does nothing regarding the PSU? It goes to PL803/5 and stops there - had me confused for a while as I was assuming maybe this was causing the fault.

Anyway, after all the time I've spent on this and reading of many other faults I reckon these Vestel boards are a complete ballache because of dry joints. But at least I'm sorted now, so happy days.

[tom66]

Re: 32" Goodmans TV

The Goodmans LCD TV is now fully assembled and passes all burn-in tests. This time I properly broke the trace between the fet and the SG2525A. Thanks for everyone's help.

Only issue is, there is a rather loud whining noise coming from the TV, I assumed this would go away when case is put back on, but no luck. It seems to be coming from the PFC transformer. Is there any way to fix this? I'm almost tempted to just remove the PFC MOSFET and leave it, as the PFC doesn't seem to be working anyway. Without a MOSFET it would just be a coil with a series diode. Maybe the switching noise from the secondary PSU is causing the noise (introducing it to the PFC coil) in which case removing the coil and replacing it with wire jumpers may be the best solution. (Of course, also removing the MOSFET, otherwise the FET would be shorting out the PSU many times a second.)

[tom66]

Re: 32" Goodmans TV

Hi Tom,

I'm gona read thro' this thread again, compare with my findings/results, then I'll get back to you, OK.

Mark

Great!

Pin #8 is definitely a source of trouble. I will do the job properly tomorrow. Bed time now...

[dumpystig]

Re: 32" Goodmans TV

Hi Tom,

I'm gona read thro' this thread again, compare with my findings/results, then I'll get back to you, OK.

Mark

[tom66]

Re: 32" Goodmans TV

Oh no, it just died after I wrote that post... I was a bit too quick.

Hmm... possibly my track break wasn't good enough. Will look into it. It was definitely working better than before...

EDIT: Yep, the pin is touching something. I will have to remove all the solder, as I twiddled with the pin and it started working. So it looks to definitely be this pin causing all the troubles.

[tom66]

Re: 32" Goodmans TV

FIXED!



Pin #8 was the problem... I broke the trace between Q837 and pin #8 of the SG2525A and it now starts up, turns off and does that all many times including between pulling the plug out, which it never did before. I'll leave it overnight to see if I can turn it on in the morning, but it's looking good .

I still left the slow start caps connected to the pin because they provide the slow starting (the set takes 5 seconds to come on, approximately) whjch might be helping to reduce the load on the supply.

I ordered some of the secondary side caps for it, but I don't think they will be necessary any more.

Oddly, the PFC bus voltage is still only 328V - which means PFC isn't working. But I guess if it ain't broke don't fix it, it seems to still be happy with the ~330V.

[tom66]

Re: 32" Goodmans TV

Hmmm

Pin 8 (of SG2525A) is looking like it might be the problem

So it's making my meter go crazy on the DC range, reading random values from -9V to +10V. On the (True RMS) AC range it reads 46V AC.

This pin definitely shouldn't have these kinds of voltages on it, but how are they getting there?

EDIT:

Okay, so this time I did it with the meter grounded to a heatsink (the FET heatsink.)

Now during start-up it measures 0V, it should be above 0.4V, preferably 0.7V. It is charged with an internal 50µA current source.