Received a somewhat rough SX-939 today in the mail from another AK'er as a "gift". Thanks Ed.(That's as far as I'll go as to ID'ing the Gentleman unless he opens up here.). It's something he wanted to do.
DAMNED GOOD KARMA!!!!!!
Nothing that follows is a reflection on Ed. I've already talked with him about the 939's problems. He knew it had problems when he got it.
Cosmetically it looks as if it's been sitting in a shop. Veneer is peeling(vinyl), and who ever had theis 1st put a 1/4 turn KEY SWITCH in for the power switch (key is one of those one for Vending Machines!WTF???????)
I'll put up some pictures in a bit. So I'm gonna have to get the Front sub panel, Front panel and a new switch. Looks like Danny @ yesterdays audio may have them all. The guy drilled out the front panels to fit the switch! The Wood ends on the front fascia are gonna need replacing also. Other than that it's not bad. (at least all the feet are there and the bottom is intact. LOL!!!!)
Opened it up and immediately saw that the Relay had been bypassed directly to the speaker switch, and one side of the Preout/main in had been bypassed. I put it on my DBT and brought it up and got no smoke. Bulb went DIM. So I took some measurements on the speaker out's while the relay was merriliy clicking along. The spkr outs were 175mv on the left and anywhee from 20mv to 300mv on the right. Shut it down marked the pots for adjusting the center voltage and bias then worked them out. Took off DBT and plugged in to wall voltage. Put pots back in position and fired it up. Managed to get Center Voltage on Left to .1mv, with right floating between +6mv and -10mv. Checked BIAS and brought it to 49-50 on left with right floating between +45-61mv erratically. But the Relay clicks ONCE and stays that way until shut down.
Emitter resistors are Ok. Pulled outputs and tested on DIODE Function. All fine. 2sb530s and 2sd388P. Regreased and reinstalled.
Found the High Filter/ Low Filter / -20Db board had a novel semi solution on the -20db. The guy had fabbed a mount for a microswitch with a roller on the arm and fastened it to the chassis so the original switch would push the micro switch closed. Problem was he wired it all 1/2 assed. Nothing wrong with the switch other than a solid layer of corrosion/sulfation that had ohmmeter showing 25K on both sides of the switch. Now less than 1oHm after cleaning. Disconnected the switch and got rid of the solder bridges on the low and hi filter switches. They work fine now.
The Mono switch was jamed in the out position. It wouldn't hold IN. DeOxit didn't do anything. The little pin in the center of the front didn't swing around like the others so I'm thinking the latching mech is FUBAR. Tore it apart, cleaned the contacts and worked the button and it popped the latch back in where it's supposed to go. Gonna leave it for now. (AWS-065-0).
Anyone with a 939 or 1010 got an extra FM push button. Mine has 2 AM buttons on it. (Left and Right! NOT!)
Plan is to rebuild P.S., Protection circuit (including Flyback Diode), Control Board, EQ, and AMPLIFIER boards 1st. Once I get the AMP settled down, I'll do the rest of the boards including the tuner if i can shake MTF loose for a few cap #'s he feels comfortable changing. NO RUSH ON THIS MARK!!! I'll let ya know ahead of time when I get close to doing the tuner.
I've got all the transistor #'s already from doing a 1010, and 737. So far haven't had one I couldn't x-ref. Plus I have most all of them in stock so replacing transistors will go for now and caps in a bit. Caps Nichicon UPW and UKL's plus the occasional Panasonic, Wima, or other film caps as needed by lack of parts.
All the lights work, except spkr A & B. The Tuner works well on a short wire, Meters move as designed, and Stereo indicator lights and sounds stereo thru headphones. Lot's of crackles in both channels indicative of the 726 and 1451 transistors. Yes MTF, mine has the 809's too so they'll get replaced(I've got the #'s. Thanks).
I think I pretty much have all the small signal Q's. And a couple of the TO-220's. Caps I'll have to make a BOM and go from there.
Larry
DAMNED GOOD KARMA!!!!!!
Nothing that follows is a reflection on Ed. I've already talked with him about the 939's problems. He knew it had problems when he got it.
Cosmetically it looks as if it's been sitting in a shop. Veneer is peeling(vinyl), and who ever had theis 1st put a 1/4 turn KEY SWITCH in for the power switch (key is one of those one for Vending Machines!WTF???????)
I'll put up some pictures in a bit. So I'm gonna have to get the Front sub panel, Front panel and a new switch. Looks like Danny @ yesterdays audio may have them all. The guy drilled out the front panels to fit the switch! The Wood ends on the front fascia are gonna need replacing also. Other than that it's not bad. (at least all the feet are there and the bottom is intact. LOL!!!!)
Opened it up and immediately saw that the Relay had been bypassed directly to the speaker switch, and one side of the Preout/main in had been bypassed. I put it on my DBT and brought it up and got no smoke. Bulb went DIM. So I took some measurements on the speaker out's while the relay was merriliy clicking along. The spkr outs were 175mv on the left and anywhee from 20mv to 300mv on the right. Shut it down marked the pots for adjusting the center voltage and bias then worked them out. Took off DBT and plugged in to wall voltage. Put pots back in position and fired it up. Managed to get Center Voltage on Left to .1mv, with right floating between +6mv and -10mv. Checked BIAS and brought it to 49-50 on left with right floating between +45-61mv erratically. But the Relay clicks ONCE and stays that way until shut down.
Emitter resistors are Ok. Pulled outputs and tested on DIODE Function. All fine. 2sb530s and 2sd388P. Regreased and reinstalled.
Found the High Filter/ Low Filter / -20Db board had a novel semi solution on the -20db. The guy had fabbed a mount for a microswitch with a roller on the arm and fastened it to the chassis so the original switch would push the micro switch closed. Problem was he wired it all 1/2 assed. Nothing wrong with the switch other than a solid layer of corrosion/sulfation that had ohmmeter showing 25K on both sides of the switch. Now less than 1oHm after cleaning. Disconnected the switch and got rid of the solder bridges on the low and hi filter switches. They work fine now.
The Mono switch was jamed in the out position. It wouldn't hold IN. DeOxit didn't do anything. The little pin in the center of the front didn't swing around like the others so I'm thinking the latching mech is FUBAR. Tore it apart, cleaned the contacts and worked the button and it popped the latch back in where it's supposed to go. Gonna leave it for now. (AWS-065-0).
Anyone with a 939 or 1010 got an extra FM push button. Mine has 2 AM buttons on it. (Left and Right! NOT!)
Plan is to rebuild P.S., Protection circuit (including Flyback Diode), Control Board, EQ, and AMPLIFIER boards 1st. Once I get the AMP settled down, I'll do the rest of the boards including the tuner if i can shake MTF loose for a few cap #'s he feels comfortable changing. NO RUSH ON THIS MARK!!! I'll let ya know ahead of time when I get close to doing the tuner.
I've got all the transistor #'s already from doing a 1010, and 737. So far haven't had one I couldn't x-ref. Plus I have most all of them in stock so replacing transistors will go for now and caps in a bit. Caps Nichicon UPW and UKL's plus the occasional Panasonic, Wima, or other film caps as needed by lack of parts.
All the lights work, except spkr A & B. The Tuner works well on a short wire, Meters move as designed, and Stereo indicator lights and sounds stereo thru headphones. Lot's of crackles in both channels indicative of the 726 and 1451 transistors. Yes MTF, mine has the 809's too so they'll get replaced(I've got the #'s. Thanks).
I think I pretty much have all the small signal Q's. And a couple of the TO-220's. Caps I'll have to make a BOM and go from there.
Larry
Ed
No heat scorching on any of the boards, which is surprising for a larger PIONEER. The PS is nice and tan. Amps show no signs of activity. None of the other boards (other than the HI/LOW/-20db board) show any signs of being worked on . No idea why that particular "retrofit" was made unless he lost the sliders in the switch which I alluded to earlier.
