Newby: Please Be Gentle.... SX-1250

Hello AK'ers!

I just picked up a SX-1250 off of a local CL ad. The gentleman I got it off of was honest and said it didn't work. I got it for a reasonable price (I thought). The unit powers on but no sound and I don't here the relay click either. It's in pretty good condition and I am willing to take a shot at it. The only thing missing is 4 of the screws off of the back metal cover. He opened it up one time and lost 4 of the 6 screws...

Where do I start? I am not unchallenged with electronics and I am willing to take a shot at it before I pass it off to a guru if needed. Are there any quick checks I can perform with a multi-meter or is this thing out of my league? I do not have a service manual but I do have the giant schematic it came with.

I currently own a SX-780, but wanted something with a little more power...

Any help would be appreciated....

Thanks!!!!!

And Hello!!!:thmbsp:

Jeff

Where are you located?

Near Buffalo NY.

With a 1250, the advice here can get you thru. Pretty sure the service manual can be obtained as well.

Be patient and careful, these amps are special, and deserve all the love you can give them. I just had mine ground-up restored, but haven't picked it up (300 miles away). This is what a 40 year old amp deserves.

Best of luck, and welcome to AK!

Are the pre amp jumpers installed in the back?
Have you tried all the inputs for sound? Not just FM/AM.
Mute switch is 20db down, you would hear something.

Powers-up? Explain.

Some may disagree but I think the 1250 is a good set to get your feet wet on. Its very accessible with the removable boards. There is some contorting for other boards but not any more that the other sets.

Check your fuses by removing them (All on the bottom board). Re-install for the PS readings.

Remove top and bottom covers. Unplug the amp boards, top and bottom Molex plugs. Have the set on one of its sides and read the voltages from the bottom of the Stabilizer board. There are AC and DC voltages - black DMM lead grounded to the chassis. You can access the pins through the white plastic Molex plugs with a sharp probe

Get familiar with this:
http://www.kallhovde.com/pioneer/sx-1250smhires.pdf

Post your readings:
pin 1 = ?
ect...

Let's see what you got! Welcome!

since your protection relay does not kick in, i'd start there. download the service man. at hifiengine. it might give a description of the protection circuit, maybe enough to give you a start. others will chime in.

Hello Zeb,

I was just actually reading the Protection board 850 issue you were responding too. I am learning to crawl at this as well. So please bare with me.

Pre-amp Jumpers?

1. I have not tried all of the inputs yet but will tonight.

2. Powers up means all of the lights come on.

3. Molex Plugs? Not too sure what those are

4. I will try and do those tonight.

I just downloaded the manual. Now time to print it. I will get those readings for you. Is it explained in the manual at all?

Pics would be really helpful...

I just glanced at the manual.... THIS IS GOING TO BE FUN!!!!!!

lol

Printing 94 pages of goodness....

Its addicting!
You will see what I'm talking about (Molex plugs) when you open it up.

Re look at my above post #5. I added a few thoughts.
Do you know how to post pictures?

Cool re-read....

And yes I do know how to post them.

I just found in the manual the "view" assemblies.

I see the stabilizer pin diagram. How do I know which ones are AC and which ones are DC

Opened her up fuses #4 and 3 are blown. Please let me know what that means?

Jumpers on the back of the unit that connect the preamp section to the amp. See pic.


With Fuses 3 & 4 blown you don't have voltage to the Main amps. It's probable that one or more of the output transistors are blown. These will have to be checked BEFORE you get fuses installed. And then we go from there. Read this thread on how to check Transistors for shorts, opens, and other faults. http://www.audiokarma.org/forums/showthread.php?t=43186 Pay particular attention to post #11. Print out the images and the text. Study it until you can draw them in your sleep You'll need to know this stuff, PERIOD!

Don't power it up until ZEB or MARK the Fixer says it Ok. Zeb has done more than a few 1250's so he know's the unit pretty well. I wouldn't know a 1250 if it came up and bit me on the a**.

Larry

No jumpers on the back. Should they be there?

I will have to resize my pics I took at work tomorrow. The files are too big. My meter does have the diode test function. I will read that other post in the interim.... we are on to something. ... I really appreciate all of the help guys!

You will have to rebuild the stabilizer board AKA Power supply. You are probably missing the function lamps for the inputs and the tuner. There is a chance that the set will play in AUX or other inputs. It would depend if you still have the 65v supply.

If you want. Lets go FWD and see what you come up with using the AUX input. Maybe a waste of time but it could prove the outputs. You mentioned the protection not working so it probably a waste of time.

If nothing then back to reading the PS pins. Following post #5.

Look at page 79 of the Manual. Pins 4 and 5 are AC, black DMM probe to chassis ground. 3 and 12 are grounds, check for continuity to the chassis. The rest of the pins are your regulated supplies in DC, the same, black DMM probe to chassis ground. We know pins 3 and 8 are missing the readings because you wont need to install the fuses.
I make a print of the board from the schematic and make notes on it. You don't have to be in a hurry and be careful in the back of the set. You are checking the pins so no need to mess with anything else.

All of this is going to be a good learning exercise because the Stabilizer is missing some voltage. looks like your in for a ride.

There is a chance the outputs are OK IF nothing else crops up.

Just chiming in to second the "don't power up until so and so tells you too" - especially once you start monkeying around in there! Unless you like running blindfolded through minefields, and even if you do you 1250 probably doesn't.

Would recommend thinking about a dim bulb tester if you are going to go any further with this on your own. I built mine per the instructions on this link: http://ppinyot.com/dimbulb/dim_bulb_tester.htm congrats on your new receiver, and have fun!

I did try aux output and nothing
The lights are out for the function lamps as well.
For the pin test do I unplug all of the moldex plugs at once or one at a time and test?

Am I checking the power supply board pins or stabilizer board pins or both? You refer to stabilizer and also ps which I am assuming is power supply