Pioneer SPEC 2

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Hi,
I am working in repair a Pioneer SPEC 2 amplifier, this amp have missing in both channels the P.T.C. thermistor (on my schematic is the Th3 P.T.C. thermistor, part number AEX-044), I don't find this part.
Anybody know which is the value ??.
Which the replacement can be ??
Could it be replaced with another thermistor's ??.
Thanks in any advice.
:att'n:
 
lorenzok38 said:
Hi,
I am working in repair a Pioneer SPEC 2 amplifier, this amp have missing in both channels the P.T.C. thermistor (on my schematic is the Th3 P.T.C. thermistor, part number AEX-044), I don't find this part.
Anybody know which is the value ??.
Which the replacement can be ??
Could it be replaced with another thermistor's ??.
Thanks in any advice.
:att'n:


Is this thermistor in the bias network? Mounted to the heatsink maybe?
I repaired a few of these amps a long while ago. IIRC the thermistor you refer to has rather fragile leads and is mounted to the output heatsink.
A wild guess would be to sub this device with a low value resistor (220 ohm)? or maybe a 1K pot. Sub a 100w light bulb for the main fuse to limit current and see what happens. It was standard procedure to use the light bulb method on amps that had unknown troubles or on the 1st try after rebuilding.
If everything else is right you can use a pot to calculate the charicteristics required for proper operation.
What failure mode did the thermistor experience?
Good liuck sir.

Rickey.
 
I believe you may be under a misconception that a PTC works like a NTC...in that you have a specific value which will change in a more or less linear fashion according to temperature. Thermal protection PTC's don't work that way...

This, from GE Sensing:
Commercial PTC thermistors fall into two major categories. The first category consists of thermally sensitive silicon resistors, sometimes referred to as “silistors”. These devices exhibit a fairly uniform positive temperature coefficient (about +0.77% /°C) through most of their operational range, but can also exhibit a negative temperature coefficient region at temperatures in excess of 150°C. These devices are most often used for temperature compensation of silicon semiconducting devices in the range of -60°C to +150°C.

The other major category, and the one that we shall concentrate on in this section, are referred to as switching PTC thermistors. These devices are polycrystalline ceramic materials that are normally highly resistive but are made semiconductive by the addition of dopants. They are most often manufactured using compositions of barium, lead and strontium titanates with additives such as yttrium, manganese, tantalum and silica. These devices have a resistance-temperature characteristic that exhibits a very small negative temperature coefficient until the device reaches a critical temperature, that is referred to as its “Curie”, switch or transition temperature. As this critical temperature is approached, the devices begin to exhibit a rising, positive temperature coefficient of resistance as well as a large increase in resistance. The resistance change can be as much as several orders of magnitude within a temperature span of a few degrees.
This is the type of device generally used as a thermal protection PTC...its resistance remains fairly constant as temperature rises above ambient, perhaps even falling a bit. But as the Curie point is reached (wonder if the famous Madame has something to do with the name?), the resistance begins to rise dramatically.

Pioneer puts the two PTC devices in series, and uses them to trigger the Q11 PNP transistor on the Meter Amp Assembly. A simple deal. The upshot of all this is that the actual ambient value of the PTC doesn't matter too much...pick your trip temperature, and you're ready to go.

Digikey sells some GE PTC devices that range in trip temperatures from 30°C to 110°C. The 80°C unit ought to be about right.

Oh...and I have a Spec 2 on the bench right now...one of the PTC's measures about 30 ohms resistance at ambient, and the other about 50 ohms.


Rickey, there is also a couple of multijunction diodes (for the bias) mounted on top of the heatsink...they aren't PTC's, but by all means they should be treated gently.
 
re Pioneer spec2

Not being familiar with this equipment, I jumped to the conclusion that the missing devices may have been in series with the O/P , but strapped out. I didn't imagine that 2 biasing thermistors would be missing. Yes, I am quite familiar with both polyswitches and NTC/PTC thermistors.
Years ago, I did have an amplifier with polyswitches, but removed them and fitted wire links.
My apologies for jumpimg to the wrong conclusion .
SandyK
 
You can thank Rickey all you like, but he is wrong. The bias diodes don't have a bloody thing to do with the circuit you're working on.

I give up...:rolleyes:

SandyK...it took me a while to look up and verify the info I posted (which I can now see was a huge waste of my time)...when I started composing, there were no replies. My post was directed strictly to lorenzok38. Apologies are quite unnecessary.
 
EchoWars said:
You can thank Rickey all you like, but he is wrong. The bias diodes don't have a bloody thing to do with the circuit you're working on.

I give up...:rolleyes:

SandyK...it took me a while to look up and verify the info I posted (which I can now see was a huge waste of my time)...when I started composing, there were no replies. My post was directed strictly to lorenzok38. Apologies are quite unnecessary.

It's been 20 years since I worked on one of these.

And of course my memory isn't perfect.

Sorry if I have led anyone astray.

Rickey
 
xmitterengineer said:


It's been 20 years since I worked on one of these.

And of course my memory isn't perfect.

Sorry if I have led anyone astray.

Rickey
No big deal...you thought he was referring to the bias diodes, but he named the part schematic designation, and even Pioneer's part number. Plus, within the last year I've rebuilt about a dozen of these, so I know them well. I wanted to help, so I gave him a ton of info, and he came back and thanked you for information that had nothing to do with his issues. I thought it a bit odd...

Such is life on the net... :headbash:
 
You can thank Rickey all you like, but he is wrong. The bias diodes don't have a bloo

Hi Echowars,

I am new in this forum and my post is previously revised by the moderator, my excuses for the delay in my response for you. First, I thank him a lot their time invested in getting all this information so complete and accurate that you sent me, it has truly been very valuable, mainly the resistance mensurations and ranges of temperature, with these data, I'll already be able to obtain a P.T.C equivalent thermistor, again my excuses for not having answered before.
I have another question about this amp.
Do you know which is the replace for transistors 2SB630A and 2sd610A ??

Thank's in advance. :att'n:
 
Pioneer spec 2 amplifiers

Ive recently got ahold of 2 pioneer spec 2 amplifiers, which both have problems. I have a tech here were i live , which im not a 100% sure of . Just wondering if there is someone out there that knows these amps well . And doesnt see it as a pain in the rear to make right . 1 amp has really bad distortion on 1 side and the protection light stays on in 1 amp. Ive already invested good money to purchase these amps , had one repaired.That cost a good chunk , but it didnt bother me to pay it because i know what i want in the end . Brought it home and it played for about 45 minutes until it started smoking! The tech seems to think its my fault , i removed a perfectly good working phase linear400 from my setup and replaced it with the repaired spec 2. That didnt last to long . Pulled the spec2 out and put old faithful phase linear back in . My system is working just fine . I find it hard to believe its my fault. Speakers are 8 ohm. He did replace the speaker terminals on the back , which on the inside the studs i noticed was very close to the heat sinks about 1/8 max maybe less . Could these arc across causing my amp to short out . It blew my output transistors he says .And he dosent understand why. He keeps saying it something wrong in my setup? Please help Thanks
 
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