A month or so ago, I got this slimline 42PJ550 Plasma set. Dead apart from a click or two.
Quick check indicated SUS_Up and SUS_Dn IGBT's short....
I pulled them and they are, 30J124 (SUS_Up) and 30F124 (SUS_Dn) devices. At the time, I didnt have those so shoved in some Panasonic IGBT's I had here, along with a 2.2 ohm F/P, that seems to fail at the same time.
Set worked--For a while, with a nice picture, no horrors usually associated with old LG sets.......
After re-tuning and settling down for a cuppa to admire my work, it made a HELL of a Bang-Like a gunshot!
Tea went one way, Dog went the other!!
I had a quick check but nothing obvious was seen actually--blown. Testing indicated one of the SUS_Up (30J124) devices I had fitted was short.
I put the thing aside in disgust! A week later I got a 42PJ350 set--virtually the same Chassis with exactly the same fault, and identical Y-SUS boards, so thought--I'll get the exact right parts for them so ordered a shed-load from China.
They turned up yesterday so I set about fixing firstly the second set, the virgin 350.
Replaced the dead IGBT's and the low-voltage elect caps around the floating-supply for good measure, 3 x 100uF and one 330uF as well as the 2.2 ohm and fired it up--That worked no probs, and I ran it for some hours.
I then set about doing the first set--the 550 I had previously buggered about with. That proved more interesting!
I pulled the four IGBT's I had fitted--and while doing that noticed a small blue disc ceramic cap--or rather only a blackened half of it, Thankfully the remaining half had its value and voltage on...
It was a 330pF 1KV device--These boards seem to have quite a few of these small blue disc caps dotted about.....
I found a 470pF 1Kv cap and fitted that. This cap decouples the Vs line and is wired across the row of big 220uF 250V caps, prob as a HF snubber-
-Hence the HUGE bang when it let go!
--So, new caps, new IGBT's and the set fired up. There was slight crackling and another HUGE Bang Thankfully no tea was at hand and the Whippets were in bed!......
The new cap I fitted--was still perfect--But close examination showed that when the first cap had exploded--it must have ejected some metal or evaporated sufficient metal onto a nearby diode's connections, attached to the heatsink.
--This had been sufficient to cause a huge flashover and another dead IGBT pair....
Diode removed and severely cleaned from the signs of evaporated metal/flashover at and between its legs (!) as I didnt have one of that type, it wasnt short anyway. Yet another new pair of IGBT's fitted and all was well, its run for a number of hours and is still running now.....
It should also be noted that I checked the 5 legged driver-devices at each and every failure of the IGBT's--they amazingly survived --in this board's case, 4 blow-up times!
So--One tiny disc-ceramic cap can cause all sorts of trouble--Even when you've changed it! I'll bet those IGBT's I first fitted would have been fine had that cap not failed.....
Quick check indicated SUS_Up and SUS_Dn IGBT's short....
I pulled them and they are, 30J124 (SUS_Up) and 30F124 (SUS_Dn) devices. At the time, I didnt have those so shoved in some Panasonic IGBT's I had here, along with a 2.2 ohm F/P, that seems to fail at the same time.
Set worked--For a while, with a nice picture, no horrors usually associated with old LG sets.......
After re-tuning and settling down for a cuppa to admire my work, it made a HELL of a Bang-Like a gunshot!
Tea went one way, Dog went the other!!
I had a quick check but nothing obvious was seen actually--blown. Testing indicated one of the SUS_Up (30J124) devices I had fitted was short.
I put the thing aside in disgust! A week later I got a 42PJ350 set--virtually the same Chassis with exactly the same fault, and identical Y-SUS boards, so thought--I'll get the exact right parts for them so ordered a shed-load from China.
They turned up yesterday so I set about fixing firstly the second set, the virgin 350.
Replaced the dead IGBT's and the low-voltage elect caps around the floating-supply for good measure, 3 x 100uF and one 330uF as well as the 2.2 ohm and fired it up--That worked no probs, and I ran it for some hours.
I then set about doing the first set--the 550 I had previously buggered about with. That proved more interesting!
I pulled the four IGBT's I had fitted--and while doing that noticed a small blue disc ceramic cap--or rather only a blackened half of it, Thankfully the remaining half had its value and voltage on...
It was a 330pF 1KV device--These boards seem to have quite a few of these small blue disc caps dotted about.....
I found a 470pF 1Kv cap and fitted that. This cap decouples the Vs line and is wired across the row of big 220uF 250V caps, prob as a HF snubber-
-Hence the HUGE bang when it let go!
--So, new caps, new IGBT's and the set fired up. There was slight crackling and another HUGE Bang Thankfully no tea was at hand and the Whippets were in bed!......
The new cap I fitted--was still perfect--But close examination showed that when the first cap had exploded--it must have ejected some metal or evaporated sufficient metal onto a nearby diode's connections, attached to the heatsink.
--This had been sufficient to cause a huge flashover and another dead IGBT pair....
Diode removed and severely cleaned from the signs of evaporated metal/flashover at and between its legs (!) as I didnt have one of that type, it wasnt short anyway. Yet another new pair of IGBT's fitted and all was well, its run for a number of hours and is still running now.....
It should also be noted that I checked the 5 legged driver-devices at each and every failure of the IGBT's--they amazingly survived --in this board's case, 4 blow-up times!
So--One tiny disc-ceramic cap can cause all sorts of trouble--Even when you've changed it! I'll bet those IGBT's I first fitted would have been fine had that cap not failed.....
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