• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

My Pioneer SX-1980 Restoration

I agree putting a old B682 in as a sub, is a poor choice. You don't even know if it is genuine part. Was it a Sanyo part?
Use a MJE1503x (PNP) device as a replacement.
If you have read these threads, you know the parts run hot because of in-sufficent heatsink area.
So beef up the heatsinks. Be creative, Mouser/Digi-key have lots of options. Can be as simply as make up your own aluminum HS. Be careful to not leave the HS live HV!!
Bottom line, the cooler they run the long they last!!
I was surprised when I figured those cheap HS are made out of steel, to cheap to use aluminum :-)
You should be able to measure the current drawn by measuring the voltage drop across the 5R6 ohm R212 and then the V drop across CE of Q211. This will tell you the Pd of Q211 and if the PS I drawn is correct. This info is based on the I drawn by each assembly, as shown in the big schematic. You can measure, add them up and post this info so it is on the record.
P.S. don't use you finger as a accurate temp measuring device.
Good Luck
Rick
 
Last edited:
Sorry, yes this is the PNP replacement from Mattsd BOM: 863-MJE15033G.
It's the biggie that attaches to the heat sink on the PSB.

The brand new transistor overheated and blew. Any idea what would cause this to run hot and blow up?
 
rcs16 said:
If you do the measurements which I asked you to do, that will answer your question.
Click to expand...

My apologies Rick, I am work right now and skimmed your complete response. I'll take the measurements this evening. Thanks again.
 
Heat is a product (literally) of the voltage and current between the collector and emitter. In my experience, the 5.6 ohm 1/2W resistor should smoke before any damage is done to the transistor (but that's certainly not a given). I'd be measuring the voltage across the 5.6 ohm resistor to get an idea of the current draw (seems as it ought to be somewhere's around 100mA, but I can't find my notes on it). If Mark has a functional 1980, maybe he'll check to see what the current is on R210 and R212. If you have a multivoltage model, make sure you're set to 120V.
 
Easy places to measure these shrouded resistors (R210, R212):

The 220uF /160V caps, + or - depending, then to the collectors of the power transistors mounted on the board's common heat sink:

be damn careful about shorts and remember your meter leads will be floating with (+/-) ~100v relative to ground

R210 5.6 ohms 1/2 watt +80v regulated supply = 0.637 volts = 114 mA ~ > 0.1 watt
R212 5.6 ohms 1/2 watt -80v regulated supply = 0.662 volts = 118 mA ~ > 0.1 watt
with a 1/2 watt resistor, at rated dissipation there is 300mA current flowing and you need more current than that to blow the resistor up. THAT'S a SERIOUS short.

measured on a working SX-1980...

IF your -80 is blowing up, UNPLUG the power amps (ALL FOUR CONNECTORS EACH)- that will remove all external load - excluding shorts on the chassis wires.
THEN it's your -32v regulator OR C221 100uF/100v

Frankly both power amps have 15 ohm resistors in series with those regulated power feeds, and anything bad enough to blow an on-semi replacement will positively smoke those 15 ohm amplifier resistors.

I'm betting on c221 backwards.
 
Last edited:
markthefixer said:
Easy places to measure these shrouded resistors (R210, R212):

The 220uF /160V caps, + or - depending, then to the collectors of the power transistors mounted on the board's common heat sink:

be damn careful about shorts and remember your meter leads will be floating with (+/-) ~100v relative to ground

R210 5.6 ohms 1/2 watt +80v regulated supply = 0.637 volts = 114 mA ~ > 0.1 watt
R212 5.6 ohms 1/2 watt -80v regulated supply = 0.662 volts = 118 mA ~ > 0.1 watt
with a 1/2 watt resistor, at rated dissipation there is 300mA current flowing and you need more current than that to blow the resistor up. THAT'S a SERIOUS short.

measured on a working SX-1980...

IF your -80 is blowing up, UNPLUG the power amps (ALL FOUR CONNECTORS EACH)- that will remove all external load - excluding shorts on the chassis wires.
THEN it's your -32v regulator OR C221 100uF/100v

Frankly both power amps have 15 ohm resistors in series with those regulated power feeds, and anything bad enough to blow an on-semi replacement will positively smoke those 15 ohm amplifier resistors.

I'm betting on c221 backwards.
Click to expand...

This is my inexperience showing. How do I measure R210 and R212?

I checked c221 and it's correct, as are the rest of the caps.
 
Turn off power.
Slide back the braided lead insulators (if present) to attach two leads to either side of the R's to be measured, using mini-grabbers. Plug other end into dmm terminals. set the dmm scale to dcv, 1 or 10V range.
Turn on power.
measure dcv across each resistor and calculate the current being drawn V/R=I, should be around 100mA.
 
The resistors are hidden under the damn heat sink, thus WHY I took the time to research and post alternate locations to access these conductors connected to the resistors.

r212 = c205 minus (the BIG axial 220uf, 160v cap CLOSER to the relays) to the mounting screw of the mje15033 pnp transistor closer to the relays.

r210 = c206 plus (the BIG axial 220uf, 160v cap, the side by side pair, the one FURTHER AWAY from the relays) to the mounting screw of the mje15032 npn transistor FURTHER from the relays.

attachment.php
 

Attachments

  • measure current.jpg
    measure current.jpg
    125.4 KB · Views: 271
Okay good. I thought I had read somewhere that I would have to desolder and lift one end of the resistor in order to measure it.
 
pognoot said:
Okay good. I thought I had read somewhere that I would have to desolder and lift one end of the resistor in order to measure it.
Click to expand...

If you were checking the resistor for it's resistance, yes. With the power off.

In this case you are measuring the voltage across the operating component. Slightly riskier. By giving easy measuring points the risk is reduced.
 
I'm not able to get a reading of any kind from R210...meter just sits at 0.00. R212 measured -.29 with the DCV range set at 20.
 
Can anyone recommend a good Pioneer SX tech in Colorado? I'd prefer someone who has prior experience on the SX-1980. Thank you.
 
r212 = c205 minus (the BIG axial 220uf, 160v cap CLOSER to the relays) to the mounting screw of the mje15033 pnp transistor closer to the relays.

r210 = c206 plus (the BIG axial 220uf, 160v cap, the side by side pair, the one FURTHER AWAY from the relays) to the mounting screw of the mje15032 npn transistor FURTHER from the relays.
Click to expand...

Mark didn't you mean c204?:scratch2:
By the way Ryan , why did you give up ? seems you were getting the exact help you needed.
 
Hey guys, I decided to pull the plug because the issues at hand were beyond my skill level and it got to the point where the endless trouble shooting was no longer an enjoyable experience for me. After 6 months of having opened up and it pieces, I was ready for a functional receiver to listen to music. After all, that's what it's about.

I want to extend my thanks to Rick, Mark, and Glenn for your help here.. THANK YOU. You guys are great.
 
We all have to all face our capabilities, like I don't fix my car or truck, since I have no lift, air tools, limited experience etc. I am past crawling on the ground to fix my stuff.
A big problem is shipping these heavy units around to fix them. The other thing is that they are not very service friendly, it is not like you can unplug a module/pcb and send it out for repair, since many of the assemblies are hardwired, which is a PITA. That and I assume that the mfg Pioneer does not even want to service their own gear, which I find to be a crime, if so, but this is the way they operate.
Have you even contacted a local Pioneer dealer, to see if they will fix the unit?
We have to get a list of regional tech's available, to help people in this predicament. I will cover Ontario Canada, even then, Ontario is huge, it takes a whole day to drive through Ontario, so there is a lot of ground to cover hear.
 
You must log in or register to reply here.
Back
Top Bottom