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Old 12th Aug 2020, 12:47 pm   #21
Freya
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

solder some temporary wires to the capacitor linked your multimeter to measure the voltage, it should give you an instant idea whats going on.
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Old 12th Aug 2020, 4:02 pm   #22
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

Have you replaced C419?
Also I had this problem once and discovered 'someone' had put the capacitor in the wrong way round...
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Old 12th Aug 2020, 4:57 pm   #23
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

Just a thought, I believe C423 (680pf) sets the frequency response of the TDA3653B output stage. If this capacitor goes open circuit the output stage might go unstable and cause the symptoms described. Might be worth checking.
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Old 12th Aug 2020, 5:14 pm   #24
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

Either you have too much voltage across the capacitor, AC voltage, incorrect polarity [we have ALL done that one!] or a very strong ripple. It must be measurable if it boils up almost instantly.
Can you disconnect the supply to the frame chip and supply it from a variable power supply or simply a test lash up that will deliver a temporary clean supply? It really can't be that complicated. It certainly is an odd one with probably a very simple answer. good luck with it. John.
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Old 12th Aug 2020, 5:31 pm   #25
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

That you mention a 'screeching' would to me suggest that something is taking-off with uncontrolled parasitic oscillations/squegging, and the capacitor is where the resultant oscillatory energy is neing dumped.

I'd be checking any and all decoupling components in and around the offending stage.
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Old 13th Aug 2020, 10:54 pm   #26
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

Found the reason for the screeching, C422 was Open. Changed C423 also and C418. Set now comes on but as C420 is useless theres no deflection at all just the horizontal line, still waiting on the replacement caps to arrive, once they do i'll have a clearer idea where to look to get the squashed vertical sorted and finally have this one fixed.
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Old 30th Aug 2020, 2:17 am   #27
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

Ive replaced the 2200uf cap and nothing, still just a horizontal line with the tiniest amount of snow visable (about a half a centimeter), I've 23.6v going into Pin 9 of the IC so supply is present, Immediatly off Pin 5 ive 15.6v, in the spec for the IC it has no minimum voltage listed just a max of 60v, is 15.6 too low? IC Cooked? C418 and R419 have gone open twice.

any suggestions?
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Old 30th Aug 2020, 3:14 am   #28
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

Replaced C418 and R419 again and now the squeeking is back...i just dont understand this chassis. its never happy to just work no matter whats done, I've never had to work on an ICC5 (yet) but id gladdly face any horrors one of those would throw up rather than this chassis. its a nightmare. going to measure that cap and see whats being dumped into it
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Old 30th Aug 2020, 3:34 am   #29
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

managed to read the voltage at C420 during the squeaking, its 38.7v, ouput at pin 5 of the IC is the same during this. Cap vented as i was reading the IC voltages so had to shut it off.
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Old 30th Aug 2020, 5:12 pm   #30
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

Reading the comments it looks that something is being overlooked, have you disconnected the frame scanning coils and checked to see if there is any continuity between the frame coils and line coils checked with megger, should read infinity, any leak could cause this sort of problem.I had similar symptoms on a old colour TV where liquid had been spilled and run down the tube to the scanning coils.
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Old 30th Aug 2020, 7:21 pm   #31
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

Finally discovered the cause of the screeching and it shouldnt happen again, Ages ago I repaired a track close to the scanning coils plug and the Horizontal and Vertical connections were intermittantly connecting due to the copper tracks being so close, i only spotted it when i got right in with a magnifier, so the vertical circut was also getting voltage from the horizontal circuit. I've fixed that so it shouldnt ever happen again, im guessing the TDA3653 has been damaged due to the excessive input voltage so Im going to change it, my supply to Pin 9 is clean at 23.6v, Im only getting 15v output at pin 5 and the manual states i should have 45v coming off pin 5
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Old 30th Aug 2020, 8:43 pm   #32
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

Replaced the IC still just a cm of snow
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Old 30th Aug 2020, 9:18 pm   #33
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

This is where im up to with it, bottom half of the screen fuctions normally (volume bar etc) when changing the screen height control only the bottom section responds the top stays the same
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Old 30th Aug 2020, 9:27 pm   #34
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

If you have now sorted out any O/V problems that was causing all of your problems to begin with you should be able to fix this now, check/replace the frame flyback diode and its associated 100uf cap, also check very carefully any low value resistors at the earthy/chassis end of the frame output, the voltage drop across this is often used for feedback purposes to the scan drive stage, only a small increase in resistance here has a massive effect on the drive available.
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Old 30th Aug 2020, 9:43 pm   #35
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

I've just replaced the flyback Diode just before i seen your message, not done the cap yet (have to see if I have one), the only really low value resistor at the output is R426, its a 2.2ohm but its measureing at 2.6, might have found the culprit, will have to find another 2.2ohm and see if thats the issue
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Old 30th Aug 2020, 11:36 pm   #36
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

Changed that resistor and that 100u cap and only the bottom filled out, top part of the screen is still the same
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Old 31st Aug 2020, 1:43 am   #37
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

Hi!

The circuit I came across gave the value of R426 as 1.5 ohms 1W!

I strongly recommend you also replace C419 in the height/linearity feedback network, make sure the 220 ohm 1W resistor across the field scan coils hasn't gone high on value or o/c – this helps to compensate for the inductance of the coils as well as C418, and I personally suggest C424 and C434 are fitted separately as two 220u 40V electrolytics each as these will share the ripple current more easily between them!

Turning to the h.t. supply, replace C508 and C509 with new, make sure either (or even both!) of the two h.t. smoothing capacitors C408 and C517 on each side of the BUT11 standby switch haven't gone rotten as well!

Double–check your h.t. supply voltage at TP501 is set for +110V exactly at zero beam current – this adjustment with VR501 is MOST important, to maximise the useful life of the LOPT and the CRT!

The height/linearity correction resistors R416/R417/R418 do often wander up in value in this part of the circuit so pay close attention to these!

Unfortunately it's not unknown for these very large "jungle" multi–everything i.c's such as the TDA8361 (U201) to develop a fault in their vertical oscillator/drive section, and this very commonly shows up as part scan/foldover such as you depicted in your picture of your set–there are three or four types of this with different suffix letters (A, E, N3 and N5) and it's important that you get the right one!

The TDA8361 and the TDA3653A function as a pair in this circuit and as I mentioned in the paragraph above, if you're certain the field O/P i.c. is behaving itself correctly, you'll have to get another '8361A of the right suffix – if the field o/p i.c. went west, the '8361A could also have gone duffy!

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Last edited by Chris55000; 31st Aug 2020 at 1:54 am.
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Old 31st Aug 2020, 9:33 am   #38
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

Maybe a cap is wrong way round? We've all done it!
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Old 31st Aug 2020, 2:12 pm   #39
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

Quote:
Originally Posted by Chris55000 View Post
Hi!

The circuit I came across gave the value of R426 as 1.5 ohms 1W!

I strongly recommend you also replace C419 in the height/linearity feedback network, make sure the 220 ohm 1W resistor across the field scan coils hasn't gone high on value or o/c – this helps to compensate for the inductance of the coils as well as C418, and I personally suggest C424 and C434 are fitted separately as two 220u 40V electrolytics each as these will share the ripple current more easily between them!

Turning to the h.t. supply, replace C508 and C509 with new, make sure either (or even both!) of the two h.t. smoothing capacitors C408 and C517 on each side of the BUT11 standby switch haven't gone rotten as well!

Double–check your h.t. supply voltage at TP501 is set for +110V exactly at zero beam current – this adjustment with VR501 is MOST important, to maximise the useful life of the LOPT and the CRT!

The height/linearity correction resistors R416/R417/R418 do often wander up in value in this part of the circuit so pay close attention to these!

Unfortunately it's not unknown for these very large "jungle" multi–everything i.c's such as the TDA8361 (U201) to develop a fault in their vertical oscillator/drive section, and this very commonly shows up as part scan/foldover such as you depicted in your picture of your set–there are three or four types of this with different suffix letters (A, E, N3 and N5) and it's important that you get the right one!

The TDA8361 and the TDA3653A function as a pair in this circuit and as I mentioned in the paragraph above, if you're certain the field O/P i.c. is behaving itself correctly, you'll have to get another '8361A of the right suffix – if the field o/p i.c. went west, the '8361A could also have gone duffy!

Chris Williams
Thanks Chris, Lots of great info there, just about to open the set up once again and get to work. I'll do what you've suggested and see how it gets on and report back.

"The circuit I came across gave the value of R426 as 1.5 ohms 1W!" -the service manual I have has it listed as 1.5ohms also but fitted in the set was a 2.2ohm?
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Old 31st Aug 2020, 2:28 pm   #40
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Default Re: Help With Vertical Circuit. Capacitor getting extremely hot

In general it is better to stay with values actually fitted to the set if they are original regardless of what the manual states, there may be mods or revisions you are unaware of.
I speak with experience here, it must have worked once with the values actually fitted and passed numerous tests at various production levels.
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