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Another 939 rebuild thread

Not that I'm aware of. PIONEER stuck with the 1451 thru to at least the end of the x3x series and possibly into the x50's. I've not seen another stock component replacing the 1451. Maybe Mark the Fixer or ECHOWARS would know.

IIRC NEC has been out of production of transistors for at least 10-15 years now. It might be a good idea to see if you can find data sheets for those transistors and compare them with the 1451 and 809 replacements that are recommended here.
 
Thanks...Zebulon1 posted in another thread regarding replacements for an SX-950:
awh-059: Q10: 2sd381: 512-ksc2073tu
awh-059: Q11: 2sb536: 512-ksa940tu

HifiEngine says the 950 was produced between 1976-8 and the 939, 74-76...I'm new to Pioneer lore having pretty much stumbled upon this prime piece...
 
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Big assumption on my part...hadn't checked the schemo and have now found the 1451 and 809 on the amp PCB. Replaced them with recommended components...this amp didn't have an 809, however; had 810s but replaced them regardless. I'm not seeing 725s on the power amp pcb, however...have 1818s or something similar; didn't write it down and the unit is now reassembled...and I am SO thankful Pioneer put transistor pinout artwork in the silkscreen! And for all of the superb information on the forum!

Did a lot of cap replacing and the transistors on the Equalizer PCB but a question...Q1/Q3 on the EQ PCB appear to need to be matched? Replaced both sets with pairs of KSA992 matched for both voltage and gain. The other matched pair for gain are across channels in the control amp PCB? Q1/Q2? I haven't even located this PCB.

Powered it up and DC offset reads 0.025V an 0.020V, but after a few minutes the heat sinks become way too hot to touch. Will check and confirm the power supply voltages before asking about the correct biasing procedure, which isn't in the manual and isn't clear from posts on this site I've searched out (which trimpot is bias, which is offset, which PCB pad number(s) to check, etc.)
 
****...are the PCB silkscreen graphics correct regarding transistor pinout? I confirmed the individual component pinouts before installation and double-checked against the silkscreen. Same with the capacitors...? (I replaced the PS caps per the polarities of the caps already installed but not elsewhere.)
 
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Amplifier Alignment, service manual page 20. Very small and easy to overlook if not at the correct magnification. Yep, bias was way way off on one channel. Now to confirm if the manual is indeed incorrect and each side should be set to 25mV instead of 50. (Set them each for 50mv.)

Heat sinks are now cool to the touch at idle. The rear right a touch warmer. DC offset is now at 1mV or less per channel.

Thank you very much to the forum for the information! Another Pioneer classic is back in business!
 
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Whoops, 30 or so minutes in it's still doing the same thing...bass is being clipped significantly regardless of EQ setting or overall volume. Will finish the entire upgrade list given and see what's up. Will say: It sounds Great while it's working correctly!
 
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larryderouin said:
Received the FACEPLATE (complete with all function switch covers, dial glass, and tuning knob back cover from Danny @ yesterday's Audio. He had it listed on the catalogue. There is a small hairline mark that is so light I had to put my camera in MACRO and get up within 6" to see it. You don't see it if you don't know it's there. Danny called it small, and boy is it ever. The glass has all the lettering in great shape, the plastic grommets are intact, the switch covers are great, and all the lettering on the faceplate is pristine. Great price too. Also got the HI/LOW/-20db switch panel, and oHm'ed it out . Get this. I ordered them Sunday EVENING and received them TUESDAY Afternoon. Less than 44 hours! WOW! The only way he could have gotten them to me faster would have been to drive from New York State to Maryland.

I tested the board with the oHm meter before I installed. Part Tested good. Swapped pins from one board to the other board. It's staying as is right now waiting on the parts from AK'er UNCLEBORT, who has graciously supplied the 3 ganged AUX power plug, the Front sub frame panel and the power switch, from a parts 1010 he has. This guy is what AK is about. I offered to pay for the parts, but he said parts are free. He declined shipping payment on the 3 gang. I'm insisting on at least paying for shipping on the subframe and switch.

For those that have 1010's and need some parts, he still does have a lot of parts for the 1010 yet. He probably doesn't have the faceplate tho. I know that the 3 gang Aux power plug, front subframe, and power switch are now gone. So check with him and ask him what he does have. He does have 3 kids, and they take up time (don't they all....and grandkids do too.) so if you need a part, be patient.

I'll take some more pics when i get the parts and do the install.

Thanks to Tom(Unclebort) and to Danny @ yesterday's audio.
Click to expand...

Is Dan still in business? It appears that his web site has expired. (https://yesterdaysaudio.webs.com/)
 
His site has been down for at least a year. He may have retired.

MAR27-2023 EDIT. Confirmed Dan retired a couple years ago.
 
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Getting some steady popping(motorboating) in LEFT CHANNEL (PHONO 1, PHONO 2, MIC ONLY) that is Volume Dependent. FM, AM, AUX is NOT AFFECTED. Source connected or NOT the popping is consistant at about 2 per second. B+ and B- to EQ (AWF-013-0) board is consistant with schematic value of 24V or -24V. No venting of Main caps is noted nor is there any other indications to me that this is P.S. related (all voltages within .25 to .5v of Bogey values on schematics. Variac to verified 120VAC). Everything else working just fine.

I did recap the board back in 2013 and replaced the 2SA725's with KSA992's. However I did not replace the 2sc1313's. I pulled the BOM from page 1 of this thread (MTF's list) for the AWF-013-0 and did a small order from Mouser. Only had to update 1 cap. (C21) 220uf 16v UKL had to bump to 35V to get a UKL 647-UKL1V221MPD @markthefixer for your info.

Will update after parts arrive and I redo the whole board, this time. Plan on checking all resistors on the board and value of Mylar caps. Styrene's will be left alone. replace all lytics and transistors (one at time on left channel until testing shows no motorboating to ID bad component, then replace all so everything new.) Fresh start for EQ Board.
 
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Probably one of the 1313's. I've decided to do the Left Channel one tranny at a time, test and keep going. Once I get the motorboating gone, just do the rest of the board as a preventative measure.
 
Actually got inside it yesterday. The only things I HAD NOT changed on the board were the resistors and the 2sc1313's. Lifted resistors and all were within 2% of nominal values. The 2sc1313's all tested good on my Chineseum transistor checker, with all have hFe between 447 and 461. BUT, I Put in 4 KSC1845FTA's with matched hFe of 425 (luckily I got 100 of them.). Plugged in a dual 1249 with a V-15-II on it and played DSOM. Then I broke out my SL-1200 (Servo Version) with a V-15-III and repeated testing. Absolutely quiet on deadwax entry and exit. No motorboating. Bad one was Q-7, as motorboating stopped after replacement.

Did notice that the bottoms of my Main filter caps were starting to bulge. Ordered 2 new KEMET
80-ALT22A153DE063
KEMET 63V 15000uF 85C

QUESTION? On the bypass caps for the Mains (which it doesn't have stock) what value would I use there. Somewhere in the .01uf range?? The resistors are going on them too. This will be the final item for the total overhaul I started back in 2013
 
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Fuxtor; Your memory is like a Bear trap!

It's finished. 2 Kemet 15000uf 63v Main filter caps (exact fit). Wish the lugs were a little longer tho. 40mm diam x 80mm length.
80-ALT22A153DE063
KEMET 63V 15000uF 85C

Added a couple .047uf 400v film caps for bypass caps. Redid a few shaky looking leads to the power supply. DBT Dimmed as expected (100W bulb). Put it on shore power and checked offset (L +0.1mv) (R 0.0mv) and Bias (Left 25mv Right 24mv) after 30 min idling. Left alone. These were last checked in 20Not going to mess with a good thing.
Still haven't done anything with the wood case from 2013. Maybe this winter when I'm between honey-do's. (Wishful thinking, HA!)
 
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