SX980 Stereo Decoder Chip Advice

Can't recommend any ebay from China chips. No way I'd even gamble on it. Perhaps buy the whole 980 board from a parts vendor on the site you mentioned and pull the chip. Or become a subscriber here and post a want ad (if that's still a thing here)
 
I don't (really?) share "UncleBingo's" thoughts on the China connection but the go find one from a donor is the sure bet.
I have been buying these chips from china and have only had good experience so-far. I hesitate to say go do it for the $18.00. Most of the chips I buy are in the 10 lot and cheaper where it's a no brainier.
The only chip I've experienced any problems with were the OP Amp's for the Technics and Toshiba EQ's and tone boards. I would buy 20 and get 12 that were good.
Good luck.
 
I guess I'd try the ebay chip and if that does not work out then are you willing to modify the unit to fit a new pcb for the stereo decoder function?
 
I think I’ll order the China chip, see what happens and go from there. In the meantime I’ll see if I can find anyone who has salvaged an 24919954-81EB-4608-AACE-ED911D37F2F4.jpeg original from an old unit.
It’s such a nice unit I’d like to have everything working as per original if possible.
 
Received the PA1001A chip from China and installed it. Powered up and the FM Stereo is now working fine! Question - after running for about half an hour on FM I checked the temperature of the chip using my finger and would say the chip is quite hot - not hot enough that I need to remove my finger but hotter than any of the other chips on the board. Anyone know if this is normal?
If it is normal I'm thinking to modify some old heat sinks I have and bond it to the chip using heat sink compound just in case.
 
Success, Good to know they are operational. Nice easy one, sort of :) I'd buy another one as a spare, maybe a good investment?
I think temp is normal, but do not know for sure, as I never tested or have a spec with DC param's to calc what it should be. I'd have to buy one to find out :)
I would think that a HS is not necessary, but the cooler they run the longer they run, usually. They seem to fail more than others. HS compound(white stuff) is not very good glue, usually use thermal conducting epoxy to attach HS's with out any restraint.

PS working on a Sanyo LA3450 design, winter has set in, it is the Cadillac of st decoder chips, imo, I will be posting it on fmtuners for a review from the experts.
 
I think we should give this matter a bit more casual scrutiny over time. First it will take some time before I can get finger temperature data on other pa1001a chips in operation, but if the circuit for some reason IS running the chip hotter than expected, it may explain the eventual failure you experienced.
It could be as simple as too much current coming in through the stereo lamp "sink" circuitry (read the voltage across (one resistor lead probe @ red dmm , other resistor lead @ black dmm probe) R37, 160 ohms) to ground.
Some circuit positions can be ruled out because the resistors involved are of such a magnitude that they wouldn't be able to pass enough current at the 13v supply voltage.
Some positions have electrolytic caps that could be passing DC. There are general electrolytics, and tantalum electrolytics.
No easy answers like using SURE-failure cssa sanyo capsistors in this one... sigh...
Some positions have ceramic caps to ground, which could be shorting out or leaky BUT these are last resort swap outs.
HAD you obtained a pa1001a from a donor card, chances are we could have easily traded out other parts from the card.\

with 12 volts, we are talking 144 ohms to pass 0.083 amp (83 milliamp) for a power level of 1 watt
0.1 watt and higher is the realm we will be exploring, and that's 1440 ohms and less while the current is 8.3 milliamps and up.
 
Last edited:
I agree to change out all the ecaps, to determine if they are trouble makers. in the phase detector ckts, pin 10-11,13-14 use low leakage Nichicon UKL. use UKL for everything ecap is fine.
markthefixer said:
It could be as simple as too much current coming in through the stereo lamp "sink" circuitry (read the voltage across (one resistor lead probe @ red dmm , other resistor lead @ black dmm probe) R37, 160 ohms) to ground.
Click to expand...
Test for Vce saturation on the internal open collector bjt. determine current through R37, solve for your internal lamp switch bjt power dissipation.
Could replace the lamp with a led and reduce this current. It is 8V/50mA spec lamp running off 13VDC.
I guess Vce sat is around a volt, so Pd = ~50mW
 
Update: Had a little setback with one of the power supply transistors that went bad along with two resistors. Replaced the defective components, DBT the unit, re-adjusted dc voltage and bias, started the unit without DBT, checked dc voltage and bias again and have been running the unit without fail and it sounds just fine! :)

One thing I noticed on the PS board while replacing the transistor (2SA850) and two resistors (6.8R's) was evidence of discoloration on the PS board in the area of the large transistors. I touched the heat sinks on the transistors (after my repairs) and they are hot but working fine during extended use. I modified some old heat sinks I had and using thermal epoxy attached them to the side of the existing heat sinks. I'm guessing that the evidence of excessive heat on the board may have been to do with failing components that were operating out of range. Anyway all good now.

PS: anyone working on the power supply boards on these unit might want to make sure they check the resistors. My experience (somewhat limited granted) is that most of the time a bad resistor shows no evidence of being defective and since it's so easy to check them with a multi meter I'd recommend this always.
 
No, the evidence of excessive heat is due to the unit being operated, probably hard, with less than adequate ventilation around the case. Pioneer always did tend to run their stuff hotter, with (in my opinion) the smallest possible heat sinks they could get away with. This made them much more sensitive to case ventilation margins. You show me a unit without heat discolored PCB's and I'll show you a unit that wasn't run very much, never run hard for extended periods, and was always well ventilated.

Heat discoloration, in my experience, takes a long time to develop.

There are SO SO many heat flow / ventilation sins everywhere BUT (usually) the output transistor areas.
 
Here is a photo showing my heat sink additions to the PS board and the PA1001a chip. Heat sinks are attached to the existing heat sinks using thermal epoxy.

*Harry - good suggestion, hadn't thought about that. I'll see how it goes and if I need to do another replacement I'll follow your suggestion. I'm thinking additional heat sink area might reduce operating temps and increase longevity. We'll see.

PS: has anyone ever installed a small fan inside the cabinet to aid ventilation? Some sort of small low speed motor with a small fan attached?

Heat Sinks.JPG
 
Fans pack the dust in. The smaller the cranny, the more dust it collects. I've posted on this several times. I've had plenty of professional experience with cooling, fans, heat sinks and whatnot. EVEN to the point of developing things that use thermoelectric coolers. THAT is expensive and precious heat ejection...

Natural convection doesn't pull it in as much, and the heat ejects it as long as the flow of hot air isn't restricted.
Of course if the air is thick with unsettled (but willing to settle the minute the air movement dissipates) heavy dust, you're screwed.
 
gregmcm said:
PS: has anyone ever installed a small fan inside the cabinet to aid ventilation? Some sort of small low speed motor with a small fan attached?
Click to expand...

all the time. you can go to the dollar store and get cheap chinese chill pads for laptops, they draw about jack 5v and have 1-2 slimline fans inside you can pirate, or watch parts express when then have semi-annual PC cooling fan sales for like $.99 each. and there are two schools of thought: you can find old transformer style power supplies-3-12v in 200-400ma anywhere, heck I have a beehive full of them, or newer cell chargers - any make. if you NEVER listen to AM radio, use the cell charger, if you plug one into the back on the switched outlet, that close to the RF board its gonna make weird noises.

but what I also do is make them blow OUTWARDS. outwards is not direct air on the heatsink, which intrinsically is the most direct cooling but its more like the fan in your laptop, pc or commercial computer equipment, it causes cooler air to come into the case along its natural and hopefully thought out paths. since heated convective air rises straight up - it has no choice - g*d said so, all you are doing is aiding and abetting the natural flow.

On my machine in the huge cherry entertainment center, I cut a hole in the back down low, with a filter (its an air intake for cargo trailer convection or sheds), and up top I have a larger 5 inch 12vdc fan and the smaller 3 inch fan, outside and on top of the stereo case, but blowing upwards. I can run bertha all day with the door closed, open the door and the inside is room temp. Bertha is a 1993 VSXD602S (needing to hit the bench for an electrolyte refresh I betcha) I have had for 24 years and is the house daily AV driver

I got a technics G something 135 amp that was broken - got too hot, desoldered it self, and it had a fan driven from a transistor network that detected a certain volume level with the 15watt surround amp on as well - screw that, I pulled some parts and added some jumpers and the fan runs 100% from the +5vdc and I beefed up that regulator (78M05) to a 1.5-2amp size (digikey). and on onkyo R400-ish machines. fine weapons but they all go bad because people put the tuners on top, in a cabinet and the -vdc regulator is un heat sunk and they all unglue themselves. easy fixes, but each one gets an internal (or external) pc fan and they never come back

lastly, looking at your pic - what you did was innovative and will be better than before BUT, fins reject heat better when the surface of the fin is flat or horizontal to the air flow - in the case of a stationary stereo - up and down, in the case of a moving motorcycle or ATV - side to side.

if you ever see a 'monolith' - those 1990-ish sony/pioneer all in ones that LOOK like stacked components but are in fact a boombox in a box with a 100 watt amp - buy it for the $1 or $2 it will sell for and scrap it, there will be 40 inches of aluminum fins inside - thats where I get my ready made home made heat sink stock...
 
Harry, unfortunately I don't have any tool to measure the temperature of these transistors but I believe the heat sink mod will reduce it for sure. I'm going to pick up a laptop chill pad/fan as per quaddriver's suggestion and see what I can do to incorporate it into my stack to aid in air flow around the area. In the photo I'm going to replace the Sansui with the Pioneer and looking at the possibility of mounting the chill pad on top of the Pioneer with the tape deck on top of the chill pad. I'll need to see if I can ensure enough clearance between the tape deck, chill pad and the Pioneer but based on one of the chill pads I've seen the dimensions look like I might be able to pull this off. If I use a transformer as per quaddriver, plug it into the switched outlet on the Pioneer and assuming no issues with noise from the fan running it just might do the job. Updates to follow.

Receiver Stack.jpg
 
SPACE OUT THAT STACK!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I have discussed this before, make sure that NO vents or heat sinks are shrouded. Fans will NOT compensate for severe restrictions!! 1/2 inch is a severe restriction!!!

I have discussed stack spacers before, up and to U shaped pieces of (painted?) wood to raise them, increasing the gap.

The arms of the U go back to front, the bottom of the U is across the front, and the side of the U is the case dimensions.
The HEIGHT is at LEAST an inch breathing room for vents and heat sinks.
 
markthefixer said:
SPACE OUT THAT STACK!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I have discussed this before, make sure that NO vents or heat sinks are shrouded. Fans will NOT compensate for severe restrictions!! 1/2 inch is a severe restriction!!!

I have discussed stack spacers before, up and to U shaped pieces of (painted?) wood to raise them, increasing the gap.

The arms of the U go back to front, the bottom of the U is across the front, and the side of the U is the case dimensions.
The HEIGHT is at LEAST an inch breathing room for vents and heat sinks.
Click to expand...

Mark, I hear you. I think I can get a one inch space between everything what I put the Pioneer into play - maybe slightly more. I think I'll use some bits I have and attach them to the existing feet of the units to get the necessary clearance. I would note that I generally don't run any of the receivers for extended periods - mostly an hour or so when I do listen to some music. Below is a photo of the chill fan I picked up and will place it between the Pioneer and the tape deck. I'm going to install it so that it is extracting air from the cabinet. I may be able to get a little more space between the Pioneer and the tape deck. I'll make it an inch clearance between the Setton and the Pioneer and hopefully an inch and a half between the Pioneer and the tape deck. I'll also raise the CD player to give more breathing room for the Marantz.

Receiver Fan.jpg
 
OK - here is the new improved stack. The photo might be a little deceiving but I have an inch between the Setton and the Pioneer, an inch and a quarter between the Pioneer and the Tape Deck ( with the chill pad resting on the Pioneer and extracting air). Also have an inch between the Marantz and the CD Player.
While doing this I noticed that the Marantz has constructed their cabinet (mine is only metal) with vent slots on the sides as well as the top while the other units only have vent slots on the top. I also noticed that the Marantz 2270/75 series WC-22 wood cases do not accommodate the side vent slots. Interesting that Marantz would choose to not put vent slots in the wood case particularly given the position of the left and right channel amp boards in these units. Seems to me vent slots in the top and sides would aid heat dissipation.

New Spaced Stack.jpg
 
quaddriver said:
how much weight is that bottom case supporting now?
Click to expand...
Not sure exactly but likely about 55 pounds. No evidence of any stress on the bottom unit cabinet. The SX-980 is almost the same size as the Setton and seems to distribute its weight on the outer edges of the Setton.
PS: did some vinyl listening with some of my favorites and sounding very very good to my ears.
 
You must log in or register to reply here.
Back
Top Bottom