Low-End Happiness

[mjarve]

I just got a Pioneer VSX-9300 receiver. It is of early ‘90s vintage, and is in rather remarkable condition, having been owned and well maintained by only one other person besides myself. The main power amp uses Toshiba 2SA1302 and 2SC3281 transistors (they look very heavy-duty), and a massive E-Core transformer. The sound is very close to my Onkyo A-7 (why, oh, why did I sell that ), with more of the warmth of a mid-70’s Marantz or Onkyo than the harshness of most 80s up consumer amps.

It does have a problem that I can easily live with or just as easily fix (the speaker relay for the “A” speakers is shot, although “B” speaker outputs work just fine). However there is an issue that, although it does not seem to present a problem right now, concerns me. There are a couple of power regulators that seem to get inordinately hot. I mean really hot. I borrowed a neighbors IR thermometer and it gave a reading of 192-degrees F(88-degrees C), and the ambient temperature of the room was only about 76-77 degrees (24-degrees C). The circuit board around these regulators is very dark, and the solder is cracked and very dry-looking (not shiny like it is elsewhere on the board). The heatsinks they are mounted to right now are obviously unable to cope with this temperature, and I plan on moving these power regulators to the larger main heatsink (which barely becomes warm after several hours of moderately loud listening). That will be a solution, but I am more deeply concerned with why this is happening. What could cause a regulator to get so hot in the first place when even the power amp is relatively cool? Is this typical of Pioneer receivers?

This is a fine audio amp, and I would like to see it run for another 10 years if possible. Is there anything I can do?

BTW: I traded my “super-charged” Sony for this even-up. I still feel I got the better end of the bargin.

[djk]

"I am more deeply concerned with why this is happening. What could cause a regulator to get so hot in the first place when even the power amp is relatively cool? Is this typical of Pioneer receivers?"

Typical design from Pioneer.

Most engineers have no idea how to de-rate for temperature and long life.

For a long time I made good money fixing the regulators in Pioneer receivers, they get so hot they un-solder themselves.

[Frank Berry]

If there is room, you might want to move the regulators and mount them on a good heat sink.
Be sure to add bypass capacitors on the input and output of each regulator. Mount the capacitors close to the regulators.

[mjarve]

Originally posted by Frank Berry
If there is room, you might want to move the regulators and mount them on a good heat sink.
Be sure to add bypass capacitors on the input and output of each regulator. Mount the capacitors close to the regulators.

What type and or value cap should I use (I'll use the highest voltage rating I can just to allow for margins)?

[maylar]

The filter caps are already in the circuit, the ones you add close to the amp are just for stability. 220-470 uF at the input, 10-50 uF Tantalum and a 0.1 uF ceramic on the output should do it.

[slowhands]

Originally posted by djk
"I am more deeply concerned with why this is happening. What could cause a regulator to get so hot in the first place when even the power amp is relatively cool? Is this typical of Pioneer receivers?"

Typical design from Pioneer.

Most engineers have no idea how to de-rate for temperature and long life.

For a long time I made good money fixing the regulators in Pioneer receivers, they get so hot they un-solder themselves.

It could be the regulator is putting out more current than it is designed to do, because an adjustment elsewhere is wrong or some component has failed. I have a similar problem with the my 1250, which is a bear to work on due to sheer weight and complexity. I fixed the regulator, only to discover the load is sucking too much power -- I have yet to ferret out the trouble.

Or it could be simply too much cost cutting, as DFK suggested.

If you are sure the load is not drawing excess current, try replacing the pass transistor with one with higher dissipation and put it on a bigger local heat sink. I would not move it far, since you could add strays or noise that could add new problems. Just beef up the pass element and its heatsink for starters. That's my two cents worth, anyway.

[mjarve]

Due to a lack of space, I've had to move the regulators in order to attach a larger heat-sink. I have the +12V, +15V, and -15V regulators mounted to a common heat-sink, which will then be mounted to the back panel of the receiver. I've been very careful to avoid allowing the mounting tabs to touch the ground, as to prevent catastrophic failure. The +5 volt unit is mounted to its own heat-sink, which will also be mounted to the back panel. I am applying thermal conductive grease to the areas of the heat-sink that come in contact with the back panel, so hopefully that will help to dissipate some heat as well. The current draw for the +12V and +5V was about 3.75A each at idle and the +15V was at about 1.45A. -15V, which had no heat-sink was about 1.05A. I am posting some pictures of what I have done so far, and a brief explanation will accompany each one.


- Power regulators mounted to new heat-sink:

[mjarve]

- 5V regulator:

[mjarve]

- Very limited area to work with:

[mjarve]

- Heat damage: