pioneer Spec4 thermistors?
- Thread starter vuntruong
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Which ones are they STV-?H? Don't the schematic/parts list in front of me.
tracing threads in this forum, it seems others have found some means to sub this part
Check out these threads
http://www.audiokarma.org/forums/showthread.php?t=279530&page=4
http://www.audiokarma.org/forums/showpost.php?p=3424904&postcount=1
I am sure "markthefixer" & "echowars" have suggestions for you, hang in there.
Rick
tracing threads in this forum, it seems others have found some means to sub this part
Check out these threads
http://www.audiokarma.org/forums/showthread.php?t=279530&page=4
http://www.audiokarma.org/forums/showpost.php?p=3424904&postcount=1
I am sure "markthefixer" & "echowars" have suggestions for you, hang in there.
Rick
I am going to go out on a limb here (not much of one, his previous posts support this), and assume the OP knows what he is talking about.
AWH-065 TH1,2 part # Th101-2
Thermistors across the 27 ohm resistors in the power limiter circuits.
http://parts.pioneerelectronics.com/part.asp?productNum=TH101-2
That got me thinking, procurement wise, they're even WORSE than a thermal bias diode, because of the paucity of information available on them, as in -zilch- ...
BUT it gets WORSE!!
There are two thermistors (across a 1k ohm resistor) in the meter driver circuits, and when inquiring Pioneer's parts database, they list them as a DIODE (and unavailable).
AWM-113 TH1,2 31d27
So, somewhere along the way we have to get resistance / temperature curves for both of these parts for the future.
So, AK'er vuntruong, please name the mystery parts!!!! We wait with bated (baited??
) breath...
Now as a side note, it occurs to me that if the misnamed part IS the thermal diode, and the OP is seeing strange things happening, the power limiter circuits themselves could be at fault. Since they contain good old (and inexpensive) 2sa733 and 2sc945 transistors, just swapping them out for new as a check won't hurt...
BUT the power limiter circuits COULD also be preventing a smoking ruin.... so be very very careful!!
BUT the power limiter circuits COULD also be preventing a smoking ruin.... so be very very careful!!
This power limiter SCR ckt was not in the SX-1250, it was introduced in SX-1280, this spec amp & other's I guess. Once it triggers, you have to cycle the bleed/power to reset it.
As Mark says it can be helpful if the op's go to the rails.
Easy to disable it, but hold on, if it is needed because of an o/p fault.
As Mark says it can be helpful if the op's go to the rails.
Easy to disable it, but hold on, if it is needed because of an o/p fault.
PM sent. (I also fix them when possible)
Why are you looking to replace two of them, are they both damaged? Could you please be more specific about "not functioning correctly".
This is a tricky and risky area to be working in if you don't completely understand the possibilities for causing major damage to the amplifier. Your calling these parts "thermistors" does NOT fill me with confidence. They are diodes, either called forward reference diodes or thermal bias diodes.
These are a very rare part, and only sporadically becoming available, usually through extraordinary means.
The crack, is it through the ears? or through the main body? Have you confirmed that the diode has gone open circuit? It has a forward voltage drop of about 1.6 to 1.8 volts at 7 mA current, and sometimes the diode test on meters cannot push enough voltage through the diode to get it to conduct.
THEN, as a very recent thread has found:
you must get any replacements installed correctly, if they go in backwards, you will damage the amplifier, SEVERELY...
Why are you looking to replace two of them, are they both damaged? Could you please be more specific about "not functioning correctly".
This is a tricky and risky area to be working in if you don't completely understand the possibilities for causing major damage to the amplifier. Your calling these parts "thermistors" does NOT fill me with confidence. They are diodes, either called forward reference diodes or thermal bias diodes.
These are a very rare part, and only sporadically becoming available, usually through extraordinary means.
The crack, is it through the ears? or through the main body? Have you confirmed that the diode has gone open circuit? It has a forward voltage drop of about 1.6 to 1.8 volts at 7 mA current, and sometimes the diode test on meters cannot push enough voltage through the diode to get it to conduct.
THEN, as a very recent thread has found:
sometimes a meter doesn't have enough voltage to push a stv-4h into conduction. A 9v battery and a 1200 to 1500 ohm resistor will do it, and then read the volts across the diode. One way will be 9v the other way will be 2.1 to 2.3 volt and sometimes the highest a meter mayl go in diode mode is 1.999 volt....
The forward voltage also varies with the amount of forward current, Pioneer (and their specification) runs them at 7 milliamps of current, and that resistor will get you into the ballpark without going over. The meters run a current quite a bit lower than that and just at the moment I think (but don't COUNT on it, I'll have to check this experimentally and edit if I was wrong (or right)) that lower current = higher voltage drop.
you must get any replacements installed correctly, if they go in backwards, you will damage the amplifier, SEVERELY...
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Thanks guys. Yeah. Not sure how the diode got cracked. Fixing the amp for my old man. The amp goes into protection mode when it gets hot. I tried to measure the idle current and bias, and notice the readings were off the charts. Then I noticed the diode ( I thought it was a resistor) was cracked.
ok, but don't be a stranger if the diode doesn't cure it. There's plenty else that could be at fault, and plenty of help here to figure it out and fix it.
