Philips 28PT44060 (L01) - Pincushion issue

[Claustrofob]

Hello!
I'm working on a Philips 28PT44060 (L01) that has a "pincushion issue".
Service manual/Schematics are here, start around page 26:
Philips 28PT44060 (L01) Service Manual


Story is... my friend came over with his TV. He had no audio in left speaker. I plugged it in, but it had sound in all speakers. He had the wrong cable or something when he tested. I wanted to try RGB on it so I plugged in my Mister with the proper VGA to SCART cable (75ohm temination and such), turned it on. Nothing.... tried a few times and eventually it turned on, but now with this pincushion issue:






I'm suspect that this issue lies within the E/W correction circuit, so that's where I've been troubleshooting. I found a MOSFET (7400) that was bad between Source (+) and Gate (-), and I couldn't turn it on with the multimeter trick, faulty indeed.
This MOSFET amplifies the E/W circuit I think?

There's alot of good testpoint so I've been using my somewhat cheap portable oscilloscope to compare with these.
As you can see below, before and after the MOSFET swap the Vpp of L4 changed but schematic says around 12-13Vpp, I get 10Vpp. And from here I don't know where to look. The Gate of the MOSFET have 3.9V so it's almost at it's max which is 4V on the Threshold so it sure is activated. From what I can recall, after changing the MOSFET the pincushion was still the same amount. Maybe a tiny bit better so something else must be bad... and this is where I'm stuck....

And the S5 is also stronger now, that's the EWdrive signal that drives the 7400 MOSFET, it's around 1.5Vpp, should be around 0.5-0.7Vpp or something according to service manual.
There's no E/W correction or Parabola parameters in the service menu on this model.

As seen on the images above. I've been starting to replace a few caps that he requested.. I usually don't do full recaps but they all checks fine in the E/W area.

Here are the measurements:



Any help would be very appreciated and I have done alot of components test to verify the state that I can answer to later!

Thanks in advance!

//Victor

[Alex KL-1]

Is possible to have simply the wrong adjusted parameters but, is good to check some parts in the E-W circuit and the HOT, such as:
2401 (ESR included)
2465
2462 and the ones in parallel
Failure in any of them will distort or shrinks the image.
BTW, for some models, the E-W correction are not fully effective and can have pincushion under some conditions.

For adjusting parameters, is needed the service manual with the access code or key gimmick.

PS.: here some very close model are in the market, with the major physical difference being the Video Component and/or S-Video in place of SCART.

[Claustrofob]

Originally Posted by Alex KL-1

Is possible to have simply the wrong adjusted parameters but, is good to check some parts in the E-W circuit and the HOT, such as:
2401 (ESR included)
2465
2462 and the ones in parallel

Thank you for helping!

The SAM (or service menu) doesn’t offer any adjustment for the E/W parameters, they’re simple not in the menu in this model. I have the key combination to access it and I’ve checked.

2401 - ESR is good
2465 - No shorts and measures 9nF
2462/2466/2467 - My model have 2466 only and it measures around 10nF.

Im not exactly sure how to measure film capacitors. I desolder them, discharge them and testing them in capacitance mode on my multimeter and also on my LCR-T4 meter. I have a ESR meter but these are film capacitors?
I also tested them on ohms mode on the multimeter and I can se that they charge up and becomes OL. The 2465 charges up really fast so I almost thought it was open.

Any tips on what to do next?

[old_tv_nut]

Measure film capacitors with the capacitor mode for correct capacitance.
High ESR is seldom or never a problem with film capacitors, as far as I know, only with electrolytics.

[Claustrofob]

Originally Posted by old_tv_nut

Measure film capacitors with the capacitor mode for correct capacitance.
High ESR is seldom or never a problem with film capacitors, as far as I know, only with electrolytics.

Ok, thank you!
Since I desoldered them and measured the capacitance one by one. I would say that these are ok that @Alex KL-1 recommended me to test.

[Alex KL-1]

The small parts near the 7400 MOSFET and the circuit labelled "panorama" (better to check these first), and parts in series with the yoke, are worth to testing, if no more idea crosses the mind just now.
BTW, adjusting the parts in the gate of the 7400 will change the strengh of the E-W actuation, butit also can distorts the intended waveform, probably, since it have some cap in it's network.

The E-W adjust probably will be with various parameters, like H parabola, H size, H bow etc, at the service menu. The code depends on manufacturer.

[Alex KL-1]

Originally Posted by Claustrofob

Ok, thank you!
Since I desoldered them and measured the capacitance one by one. I would say that these are ok that @Alex KL-1 recommended me to test.

Yes, statistically, for these modern CRT TV's, the parts that makes more trouble for it, are those mentioned or the ones near it (the ones that "conducts" part of the H sweep current).

[Claustrofob]

Originally Posted by Alex KL-1

The small parts near the 7400 MOSFET and the circuit labelled "panorama" (better to check these first), and parts in series with the yoke, are worth to testing, if no more idea crosses the mind just now.
BTW, adjusting the parts in the gate of the 7400 will change the strengh of the E-W actuation, butit also can distorts the intended waveform, probably, since it have some cap in it's network.

The E-W adjust probably will be with various parameters, like H parabola, H size, H bow etc, at the service menu. The code depends on manufacturer.

According to the service manual on page 68, panorama is only for 16:9 sets. This is a 4:3. And I don't have that circuit on the chassie of this model.

There's no parabola parameters either in the service menu of this model. I can show you later what I have.

I've checked all parts in the EW circuit and they all checks fine but will check again.

The last thing to check is everything in series with the yoke, I guess.

I noticed yesterday that L3 is very unstable, jumps from 130-150 V back and forth. I don’t know if that’s normal?

[Alex KL-1]

Originally Posted by Claustrofob

According to the service manual on page 68, panorama is only for 16:9 sets. This is a 4:3. And I don't have that circuit on the chassie of this model.

There's no parabola parameters either in the service menu of this model. I can show you later what I have.

I've checked all parts in the EW circuit and they all checks fine but will check again.

The last thing to check is everything in series with the yoke, I guess.

I noticed yesterday that L3 is very unstable, jumps from 130-150 V back and forth. I don’t know if that’s normal?

Is good to not take any measurements from L3 test point, since it can have up 1500V of peak voltage (the retrace interval), so it plays havoc or destroy meters.

The E-W MOSFET is feed from µC as show in the schematic?
Since you have schema, also not hurts if you play a little with the R values near the E-W MOSFET. Any bad progress and you can revert to original.

[Claustrofob]

Ok, thanks!
Since L3 stated 140V MainSupply, I thought it was safe to measure. Will be careful in the future.

Yes, the EW MOSFET 7400 is driven by the EWdrive coming from the µC.


As you can see, S5 is the signal driving the MOSFET, and as I stated in my first post. My S5 signal is a bit too high, right? almost 1.3Vpp. Should be around 0.7Vpp right? And also 4V when measuring with DMM.

I've been playing with resistor, before and after the MOSFET. Although I did put resistors in parallell so I managed to destroy the MOSFET doing that. I should have put the in series or swapped them out. What I found was if I decrease the gate voltage the pincushion becomes more prominent. Which makes sense.

Any recommended resistors that I should try changing and recommended values?

[Alex KL-1]

Probably the gate of MOSFET was damaged due to some ESD...

This voltage needs to be adjustable, since Vgs(th) varies for each MOSFET, and each CRT can have different final adjustments, so is intriging to see no service mode correction for it... especially since it indeed are supplied by the TDA95XX.

Having fixing these type of TV for more than 4 years, I noted that are indeed variable the setpoints for V and H settings, due to tolerances.

I just remembered something... some sets, I don't remember the maker, had 2 different service modes; one being for common adjustments, and other for advanced. Also, some have a messy menu, with H parameters spread in all pages of service mode, or with uncompreensible abbreviations.

[Claustrofob]

Hmm… interesting!

Page 13 in the manual (link in first post) says something about SDM and SAM.
”Service Default Mode (SDM) and Service Alignment Mode (SAM)”
And I’ve managed to enter the SAM menu and checked the geometry parameters. Maybe I have to dig deeper but I feel like I have done that.
I’ll check tomorrow and reply back.

Thank you for your help!
Really appreciate it.

[Claustrofob]

Originally Posted by Alex KL-1

so is intriging to see no service mode correction for it... especially since it indeed are supplied by the TDA95XX.

Having fixing these type of TV for more than 4 years, I noted that are indeed variable the setpoints for V and H settings, due to tolerances.

I just remembered something... some sets, I don't remember the maker, had 2 different service modes; one being for common adjustments, and other for advanced. Also, some have a messy menu, with H parameters spread in all pages of service mode, or with uncompreensible abbreviations.

These are the possible adjustment paramters available in the (SAM) service menu under geometry:

• HP 30
• HB 32
• HSH 32
  
• VSL 32
• VAM 36
• VSC 20
• VSH 30
• SBL OFF
• H60 9
• V60 -2

I tried adjust these but none was fixing the pincushion for me.
My next step will be to replace all the componentes in the EW circuit and the above that you mentioned. Mostly the filmcaps and diodes if there's something hiding that I can't see when measured. Trail and error if you will.

I'm getting a bit desperate here

[Alex KL-1]

If some parameters not have any response, or only a paltry response, the TDA also can have some damage related to it's function or E-W pin output. We hope not...

[Claustrofob]

Yesterday I made some good progress!
I read more about the "How to change an Option Byte" in the service manual and then I compared what this model should have. Turns out, they were wrong!

Current Options Byte parameters
OP1 - 4
OP2 - 196
OP3 - 0
OP4 - 8
OP5 - 240
OP6 - 0
OP7 - 67

What the 28PT44060/01 model should have:
OP1 - 4
OP2 - 196
OP3 - 224
OP4 - 40
OP5 - 228
OP6 - 0
OP7 - 67

... and voilá! I now have the EW parameters available.
I guess this is a method to enable features that comes with the model/type of chassie in each model?

Anyway, this means that somehow/someone must have accidently changed these parameters when fiddling around in the service menu. I know I didn't!
I can now expand the picture and reduce the pincushion and finally adjust to a good looking geometry!

Super thanks to @Alex KL-1 for all your support and help! The part where you mentioned that 7200 was controlled from the TDA95XX, that was the moment I started to read more about the Option Bytes.
Thank you for that!