Pioneer SX-450 Output Transistor replacement

[camgilbert]

Hello,

I have acquired an SX-450 with a blown (like cracked in half) D313R output tr.

I have TIP41CTU's new from another project.

Does anyone know if these will work on this receiver or do I need to look at:

MJE15032G which were mentioned in another thread.

Many thanks

Cam

 

[quaddriver]

In most cases, a 2SD300-something can be equally replaced by MJE15032/33's (if there is a 2SD isnt there also a 2SB or is this quasi complimentary?) but I myself am about to try the TIP41/42s on a nikko that is equal in stature. In the smaller stuff I have used both but I generally mimic the lessons learned from here.

And, if you have a post from Markthefixer mentioning a certain sub in a pioneer, use that sub like it was the word of G*d

 

[dlucy]

The TIP41C will certainly handle the needs of the SX-450

https://www.fairchildsemi.com/datasheets/TI/TIP41C.pdf

The MJE15032 are more made-for-this-application and might do a better job (lower noise or less distortion in audio range) but are way overkill for the 20W output of the SX-450.

https://www.mouser.com/ds/2/308/MJE15032-D-95003.pdf

If you got TIP41, give them a try.

 

[dlucy]

The TIP41C will certainly handle the needs of the SX-450

https://www.fairchildsemi.com/datasheets/TI/TIP41C.pdf

The MJE15032 are more made-for-this-application and might do a better job (lower noise or less distortion in audio range) but are way overkill for the 20W output of the SX-450.

https://www.mouser.com/ds/2/308/MJE15032-D-95003.pdf

If you got TIP41, give them a try.

There is an issue to be avoided when replacing output transistors, that of the fT being too high now (with modern transistors). One way to solve the dilemma, if I understand it correctly, is to make sure the output transistors have a frequency-limiting cap on the collector. This prevents the better newer higher frequency output transistors from overheating while trying to amplify stray RF signals in addition to the audio frequency signals you are intentionally delivering.

Some of this can be found at this post and above: http://audiokarma.org/forums/index....ansistor-in-power-supply.688206/#post-9191716

 

[camgilbert]

thank you all!!

 

[camgilbert]

Hi all,

So I replaced the 4 x D313R with 4 x TIP41C and it blew the 2 x 4A Fuses on the power board.

It did appear that R222 heated up prior to fuses going.

I have a DBT but assumed this would be a straightforward swap.

Any thoughts?

Thanks

Cam

 

[dlucy]

I replaced the 4 x D313R with 4 x TIP41C and it blew the 2 x 4A Fuses on the power board.

It did appear that R222 heated up prior to fuses going.

So, you have one or more failed/failing components prior to the output transistors that are allowing them to draw far too much current. That's what my hobbyist-level expertise is telling me.

I would check the resistors surrounding the output transistors carefully, the diodes, and the caps. Luckily, this board is easy to get to.

 

[quaddriver]

ok, you need to take a step back.

its not necessarily true, but can be likely that your brand new outputs are blortlecated. remove them. now take a look at the C1318 and A720 drivers (easily replaceable) and lift and test the 5.6, 82 and 150 ohm resistors and the STV3 diode (there is a thread somewhere on how to make a new one from other stuff in case they are bad)

if these are ok/fixed, then you should be able to get sound and no fuse blow from just them into headphones (but I admit, in a quasi-comp setup Im not sure how clean it will be)

the service manual btw, is here, for free in the pioneer section (page 4)

 

[gslikker]

Maybe such could happen, if you pulled or replaced Q210 BUT put it in as per the schematic, as some stupidass did draw it the wrong way around in the schematic I have.
It is the schematic from hifi engine. It is wrong.

This just additional to the comments above.

 

[dlucy]

This is the corrected version AFAIK

 

[dlucy]

A zoom in on one channel so we can help

 

[camgilbert]

Hey guys,

So it looked like the Q213 (TIP41C) blew again. (this was the original location of the TR (a 2SD313R) that had burned up when i got the receiver)

So I am now on a DBT.

I replaced the bad tip41C and replaced a couple of resistors that heated up in the prior process.

So we should be back to clean but with the short as the lit 60w bulb is confirming!.

So I took some readings:

Question: In my experience under the DBT with different amps I always get a lower than proper voltage (like 1/2) when taking measurements. Does that make sense?

So, with that in mind, i worked my way from the fuses out and found 8V on R307 the 470ohm 2W resistor and zipola! on R308 its negative partner.

Any thoughts on why i would be getting no voltage at that point? Things to check?

The Red Herring: This SX-450 has the LED upgrade kit for the 3 main front panel bulbs. When the receiver is turned on (with DBT) the LED's sort of glow in and out prior to settling in at their fixed brightness which is lower than normal on the DBT. This lasts for about 2 seconds.

Many thanks!

 

[dlucy]

Have you measured the emitter resistors R233-R235 out of circuit?

 

[dlucy]

And you'll need to pull R221 and R222 out and measure them. That's the spot where you'd put in a trimpots if you wanted to make this adjustable.

https://m.facebook.com/media/set/?set=a.10208946084508535.1073741872.1208612974&type=1&l=bf3cb01537

 

[quaddriver]

disconnect everything if you can and test all voltages from the power supply.

edited to add: while not on the dbt. see if you can get rid of the +/- rails from going anywhere and even the regulated stuff. does the power supply spit out what is advertised?

 

[camgilbert]

HI,

I thought it might help to show an image of the problem TR.

When I got the unit that TR to the far right, was broken in half, burnt and the -25V rail (brown wire), along with the 150ohm resistor were also burnt off.

in that state the unit would turn on with distortion on one channel

With the main board burnt, I could not solder to it, so I came up with solution shown.

As is, if I take off DBT it will blow that transistor and the 2 4Amp fuses.

I have replaced a few components, the 4700uf Caps, the 2 x 470ohm resistors and the 4 x Diodes D305-D308 and a couple of burned resistors.

From experience I have learned it is perilous to start replacing components so I'm wondering if someone who understands the circuit better than I can troubleshoot how to work back from that transistor to potential components that could be causing the issue.

 

[camgilbert]

Sorry one more piece of info:

If I disconnect the brown wire shown above, I get a perfectly working right channel and and a ground hum through left channel. (Using headphones)