Question about Panasonic PT-51HX40 51" Rear Projection Television
Panasonic 51HX40 problems after IC substitution
Texasdan has the right answer, especially with regards to the Panasonic convergence circuits that use STK392-110.
110 IC has specific design parameters relating to idle current and junction resistance of the 6 semiconductor op-amps (current amplifiers) in the STK package.
Panasonic engineers are very clever, they have designed and built millions of TVs. They designed this convergence output circuit to work with 2.2 ohm resistors, 110Cs and the convergence yoke, all in the same current amplifier circuit. They are like 3 DC resistances in series between the supply voltages and ground.
Changing the value of the total DC resistance or DC resistance of any component in the circuit will result in incorrect operation because the bias voltage will be wrong at the top of the 2.2 ohm resistor and fed back to change the gain of the op amp.
Using 150 or 180 ICs usually causes the 2.2 ohm resistors to smoke or the power supply safety protection circuit to shut the TV down. Sometimes the ICs are damaged from the over-current condition
The equivalent junction resistance of the op amps within the STK 392-110 is different than the value for 120, 150, 180 and other ICs. (This value is determined by JR = JV/JI, Junction resistance = Junction Voltage/Junction Current)
120 can safely substitute for 110 ICs because the junction resistances are very similar and within the design tolerance of the circuit.
Junction resistances for 150 and 180 ICs are not so close and the resistors usually burn up or cause shutdown conditions or premature failure of the IC.
If you fix other makes, you will be familiar with the Hitachi Service Information regarding substitute ICs. They re-design the circuit and change all of the low ohm resistors to different values to accommodate the difference in the junction resistance between 110 ICs and 180 ICs. This is required with all Hitachi STK substitutions.
Also look at the schematic for the most recent Hitachi rear projectors (51F500, etc.). They use STK392-150 and STK392-110 IC in the same chassis and they have to be replaced correctly. If not, callbacks occur with smoked resistors or pre-mature IC failure. This is because they are different ICs with different specs.
In the Panasonics, if you replace the 110 ICs with STK 392-110 or 120 ICs things should be OK. Of course the 2.2 ohm resistors may have to be replaced. These resistors can measure normal (2.2 ohms) and appear normal with no power. When power is applied, the resistor heats and increases in value or opens to cause the power supply safety circuit to shut the TV down because an over-current condition occurs on the and - supply voltages. (because the voltage at the top of the 2.2 ohm resistor controls the gain of the op-amp. Too much gain=too much current=damaged ICs or resistors)
Proof is to operate the TV with the ICs removed or power removed by un-soldering the IC pins.
Do not believe the Internet shopping cart boys, they sell stuff, they do not repair Panasonic TVs, or they would know. The 110-120-150 and 180 ICs are all different. The higher number does not mean better or new and improved, just different.
Some makes of TV may operate with 150 or 180 ICs, many times the substitute ICs cause resistor burn-up, power supply shut-down or IC failure. Especially sensitive are Panasonic and Hitachi TVs. If you want to use the 150/180 ICs, re-design the circuit and change all of the resistors.
120 ICs can be safely used for all TVs with 110 ICs because the specs are very similar.
I don't mean to be too rude, but... anyone that suggests replacing 110 ICs with 150 or 180ICs and doing no circuit modifications to accommodate the substituted parts, has no real knowledge of how the ICs or the convergence circuit works. They will also have plenty of callbacks and problem TVs to deal with. Usually they blame other unknown failures when the TV can't be repaired to normal operation.
Posted on Sep 14, 2010
Only use the same part number when replacing convergence amps, or you will need to replace all of the power resistors with recommended values for the convergence amps subsituted.
Posted on Sep 30, 2009
Terry and Dan are 100% correct. Use only the same exact IC unless you are 100% sure the substitute chip works in your TV. An example is in Hitachi you can almost always sub 110's with 150's...but anything else is a risk. When doing these repairs if you want to take the guess work out of the equation get a repair kit from sites like www.TvRepairKits.com
Posted on Jun 11, 2011
I have noted several times this statement...STK392-110
upgrade to STK392-180 or 150s.....my main OEM supply
house Andrews Electronics reports that is incorrect substitution
Best and only upgrade I use is -110 to STK394-160 Hitachi part
CZ 01341, Mfr actually Sanyo......List location and original part
number and sub you used so far for help-----.................T
Posted on Dec 09, 2007
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Posted on Jan 02, 2017
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