Running Hot After Fresh Recap

[Pageplayer]

Hi Guys,
I just completed a Recap on a SX-1050 a few days ago. Did the Power Supply A & B boards and the Protection boards, including most transistors. And only a couple of the larger caps on the Power Amp board. The unit is up and running for the most part, but to me it seems to be running hot. Let me explain..

When touching the Heatsink that's directly attached to the AWR-103 board, it's very hot.
I put my thermocoupler that came with my DMM on it and it's reading 135 - 138 degrees. Not sure if this is normal.
Also, I work in my garage and the last week has been a scorcher. In the afternoons its been about 97 degrees outside. When its that hot in the garage, the SX1050 protection relay starts to cycle off and on. In cooler morning or late evening temps that receiver with stay running without a problem.

I have checked and set the Idle current and DC offset on the speaker terminals a few times and they seem pretty stable.

I recorded the voltages on the power supply AWR-103 and Protection board AWM-090 and notice a few discrepancies.. (highlighted)

Power Supply AWR-103
Pin #01 +22.6 vdc should be +24v
Pin #02 +74.4vdc should be +76v
Pin #03 -76.5vdc should be -76v
Pin #04 0vdc (ground) .3 ohms
Pin #05 +13vdc should be +13v
Pin #06 +13vdc should be +13v
Pin #07 -12.8vdc should be -13v
Pin #08 -60vdc should be -60v
Pin #09 -30vdc should be -30v
Pin #10 -24.6vdc should be -25v
Pin #11 -24.6vdc should be -25v
Pin #12 0v (ground) .9 ohms
Pin #13 +31vdc should be +25v
Pin #14 +31.3vdc should be +25v
Pin #15 +37.5vdc should be +30v
Pin #16 +73vdc should be +60v
Pin #17 +73vdc should be +60v
Pin #18 +5.28v should be +5.4v
Pin #19 +5.28v should be +5.4v

Protection Board AWM-090
Pin 1 0v (Ground)
Pin 2 -12.8V should be -13v
Pin 3 +7.67v 8V Lamps
Pin 4 +.096V = jumping .022 to .040
Pin 5 +.097V = jumping -.002 to -.015
Pin 6 -.109V = +.018 (Running low and positive ?)
Pin 7 -.108V= -.018 (Running low ?)
Pin 8 0v (Ground) Getting small + & - fluctuation
Pin 11 0v (Ground) Getting small + & - fluctuation
Pin 12 +60V = +72.7v

I'm about to start checking pins on all the transistors.. but was wondering what you guys think about the temperatures and voltages.

Thanks in advance!
Chuck

 

[markthefixer]

Your positive voltages (pins 15, 13) key off of pin 16, ten percent AT WORST variation from schematic, thus 66v is your upper limit.
Same for pin 8 (-60v) which is spot on.
Looking at pin 2, that is the raw DC going in, and that tells me Q1 is turned on hard or shorted, definitely not regulating.

The heat is too much voltage into the power amp circuits - it should cool down when the +60v is correct.
Also the pins 4,5,6,7 of protect board are wonky due to the +73v where there should be +60v. That should come into line when the +60 is fixed.

Pins 2 and 3 being raw dc input are allowed quite a latitude, but less than 65 I would be concerned - so not a problem.

your protect could be DC on pins 8 & 11, but we can skip reading them as they are intimately connected with pins 4,5,6,7 so those readings suffice.
(that means that pins 4 & 5 have 1/2 ohm of resistance to pin 8 which is the output pin of the power amp)
It could also be a weak Q7 2sc1384 which we replace with a ksc2690.
D5 (33v) on the protect board is probably running hot too because of the +73v instead of +60v

post ecb voltages of q1, q2, q3 - check power supply for mis- installed q2 or q3 the to-220 q1 2sd313p transistor is hard to get in wrong.

 

[Pageplayer]

Mark!
It's a honor to have you troubleshooting my issue. Thank you

Here's what I got from the protection board.
Q1B +18mV (KSC1845FTA)
Q1E -.004V
Q1C +18.5V

Q2B -.10 to 27mV jumping around (KSC1845FTA)
Q2E -.004V
Q2C +18.5V

Q3B -.071V (Original 1616GBU)
Q3E -.53V
Q3C +18.86V

Q4B -.040V (Original 2SC945A)
Q4E -.626V
Q4C +25.8V

Q5B +18.7V (Original 2SA733)
Q5E +17.2V
Q5C +1.5V

Q6B -1.5V (KSD1616AGBU)
Q6E 0v
Q6C +11.7V

Q7B +11V (KSC2690AYS)
Q7E 10.5V
Q7C +10.7V

Thanks again!

 

[Pageplayer]

Oh Boy.. I failed... Q3 on the Power Supply is not installed correctly. Let my unsolder that and flip it around.. Stay Tuned.

 

[Pageplayer]

Here's what I get now..

Power Supply AWR-103
Pin #01 +23.6 vdc should be +24v
Pin #02 +76vdc should be +76v
Pin #03 -76.5vdc should be -76v
Pin #04 0vdc (ground) .3 ohms
Pin #05 +13vdc should be +13v
Pin #06 +13vdc should be +13v
Pin #07 -13vdc should be -13v
Pin #08 -60vdc should be -60v
Pin #09 -30vdc should be -30v
Pin #10 -24.3vdc should be -25v
Pin #11 -24.3vdc should be -25v
Pin #12 0v (ground) .9 ohms
Pin #13 +25.3vdc should be +25v
Pin #14 +25.4vdc should be +25v
Pin #15 +31.5vdc should be +30v
Pin #16 +62.0vdc should be +60v
Pin #17 +62.1vdc should be +60v

Protection Board Checks good too!
Awesome.. I'm Subscribing right now!

 

[markthefixer]

Power supply voltages look good.

Ok, dial in the amp outputs (dc balance adjustment ("10.3") in the manual - we tend to call it dc offset) to 0.000v, then set the idle current - ALTHOUGH you would be best served by replacing the idle current trim pots first.
The idle current pots might go open circuit if the pot wiper hits a corroded section of the center tap's commutator / slip ring, that's $$$$ BBAAADDD. The outputs and drivers instantly self destruct!!
if not replacing the idle current trim pots WITH THE POWER OFF exercise them a bit, then set back to about the same position and set the correct idle current. Then go back and tweak the amp outputs back to 0.000v

BTW I was looking for POWER SUPPLY board q1, q2 and q3 readings, not the protect board.

 

[Pageplayer]

Thanks Mark,
Ya, I wasn't sure if I needed both protect and PS voltages so I went ahead and started on the protect board.. I should have double check pinouts before posting.

I had already adjusted idle current and dc offset immediately after flipping the backwards Q3. But do you happen to have the Mouser P/N for the trim pots?

Appreciate that you took the time to point me in the right direction. Thanks.

 

[markthefixer]

My bad, usually I am more explicit.

652-3386H-1-501LF 500ohms 3386H Single Turn 3/8" ? 10% parallel to pcb
sx-1050 idle current adjust

652-3296P-1-202LF 2Kohms 3296P Multi Turn : 12 3/8" Sealed parallel to pcb
SX-1050 offset voltage adjust

 

[Pageplayer]

Thanks! The trim pots have been added to my Mouser shopping cart.

I hope it's ok to change the subject, but I thought you all would get a kick out of what I picked up today, and I thought some input from you all may help me get started off on the right foot..

So, this morning I see a SX-950 on ebay from a local seller that was stated only as "It lights up". So I figure what the heck, I'll make an offer and see what happens. Well, lo and behold he takes the offer and 90 minutes later it's in my possession!

Now, other than being dirty like most "As-Is" items are, It looked to be in fairly good condition.
But before plugging it in, I open it up and notice the relay has the cover off and the guts missing, and it's hot-wired to bypass itself! YIKES,
Sure enough, upon closer inspection I notice some burnt up resistors on the power amp, Left channel side.

I already had planned on recapping this unit so I not upset, especially since the price was fair.
But, How do you think I should proceed with troubleshooting this?

And yes, I already have a dim bulb tester.

 

[Watthour]

There are several things which immediately com to mind for the SX-950, but that's probably better in its own thread, instead of confusing this one.

 

[markthefixer]

Correct, new thread. Then get manual, and list the parts numbers of the burned resistors.

That will help teach the roadmaps and component identification.

Short form: burned resistors can be amp channel blown, transistors including outputs will be needed in addition to resistors and whatever else.
But this is what things look like when an idle current trimpot lets go.
.

 

[rcs16]

No image?

 

[Pageplayer]

I'll start a new post and some pics tomorrow night..