SX-1280 HELP W/power supply

D

dognut

Member
Hello to all from south florida.Just picked up a 1280 with a few problems.Unit works using cd player in AUX in. FM reception stinks & no AM but the meter swings hard to the right.Tone controls don't work.It had very scratchee volume control.Last night I deoxed & lubed all controls & switches.That 2nd row of circut boards was a pain.OK, this morning using a variac at 120vac,I checked DC ballence floating between 1.5 & 5.0 mv. Idle was at zero & unable to make any change on the trim pot. Heat sinks are warm to very warm. I then checked the Power supply AWR 157 terms. 6&7 133.2vac this is fuse power.term.8=+8.5,term.11,12,13=+0.7,terms. 20,21,22=-30.8 terms.25=-43.6, terms.16,17,18=+13.6 I can see that the 68v & 32v rails are wrong.Tonight after work I will try to take readings with the circut card removed.I am not a electronics repair guy but am a controls tech at the local nuclear power plant.I think with your help I can repair this unit.Thanks in advance, tom There are no nasty burn marks,all caps look good.It looks like someone in the past has reflowed some solder joints,soldered some wire posts,replaced a chip on the tunner board & some resistors look to clean to be original.Again, thanks, tom
 
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dognut said:
I then checked the Power supply AWR 157 terms. 6&7 133.2vac this is fuse power.
term.8=+8.5
term.11,12,13=+0.7
terms. 20,21,22=-30.8
terms.25=-43.6,
terms.16,17,18=+13.6

I can see that the 68v & 32v rails are wrong.
Click to expand...

The thread in the quote below should help, mostly with parts numbers (mouser.com)
Considering the straightforward nature of the regulators (no "interdependence" - like tracking...), and the parts costs, throwing in the fact that Pioneer heat stressed their power supplies, the best advice I can give is to rebuild the regulators - setting the clock back to "new"...
All 4 transistors are suspect, and caps dry out. the Zeners could have been stressed during the failure, so at a nickel apiece - replace them... That logic now encompasses the entire provided parts list...

also you will need:
534-4673 to-220 mica insulator $0.14
532-249 1 oz thermal compound $4.71


markthefixer said:
Look for these voltages on the AWR-157 board:

pin 8 +68v
pins 11,12,13 +32v
pins 20,21,22 -32v
pin 25 -68v
pins 16,17,18 +13v

rebuild / replacement parts:

q1 2sd712 100v 4a 30w:
512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54

q2 2sb682 100v 4a 30w:
512-KSA940TU_Q pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54

q3 2sc1914 90v 0.05a 0.2w:
512-KSC2310YBU to-92 ecb 150v .05a .8w 100mhz 40-240hfe $0.11 ea

q4 2sa904 90v 0.05a 0.2w:
512-KSA910YSHTA to-92 ecb 150v .05a .8w 100mhz 40-240hfe $0.07 ea

q5 2sb682 100v, 4a, 30w:
512-KSA940TU_Q pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54

q6 2sc945 50v 0.1a 0.2w:
512-KSC2310YBU to-92 ecb 150v .05a .8w 100mhz 40-240hfe $0.11 ea

q7 2as945 50v 0.1a 0.2w:
512-KSC2310YBU to-92 ecb 150v .05a .8w 100mhz 40-240hfe $0.11 ea

D1,2,3,4,11,12:
512-1n4004 conventional rectifier 1a 400v $0.06 ea

D13 6.1v 1/2 w zener:
512-1N5234B Fairchild 6.2V, 0.5W Zener

d7,8,9,d10 32v 1/2w zener:
512-1N5257B Fairchild 33 V, 0.5W zener $0.05 ea


c5,c6 470uF 100v axial leads!! 647-TVX2A471MCD $2.19 ea
c7,c8 220uF 80v (100v) 647-UPW2A221MHD $1.26 ea
c11,c12 22uF 35v (50v) 647-UPW1H220MDD $0.19 ea
c13,c14 10uF 35v 647-UPW1V100MDD $0.11 ea
c15,c16 330uF 25v (50v) 647-UPW1H331MPD $0.65 ea


c18,c19 1000uF 16v (25v) 647-UPW1E102MPD6 $0.64 ea
c20 1000uF 25v (35v) (50v) 647-UPW1H102MHD$1.26 ea

c21 33uF 25v (50v) 647-UPW1H330MED $0.24 ea
c22 100uF 16v (35v) 647-UPW1V101MPD $0.32 ea
c23 22uF 10v (50v) 647-UPW1H220MDD $0.19 ea
c24 10uF 10v (35v) 647-UPW1V100MDD $0.11 ea
Click to expand...
 
sx-1280

Hello to all. Finshed rebuilding the power supply board awr-157. I used the mark-the-fixers cap list only I searched the mouser catalog & found all the exact voltage caps. There there,cost a few cents more.I allso replaced all the resistors with 1% wire wound 1/2 watt.Reciever now works.Got the dc balance & idle current right were it belongs.Got my tone controls working.Now I still have poor fm & no am.Allso the meter swings hard to the right when on am.While I am getting ready to recap the power amp boards awh-074 & regrease the heatsinks I am going to recap the tuner board & replace the transistors.QUESTION! am I on the right track with the tuner board???????? Thanks, tom south florida
 
Dealing with a tuner section and properly calibrating is a job for the pros. Mark will have a suggested person for the job, but it means shipping your receiver. You could look locally or ask here on AK if there is a person near you that is qualified for tuner work. The tuner requires very specific test equipment to get it right.

Glad to hear your refurb went well. Good luck on the rest of it. BTW, welcome to another Florida AKer.
 
The extended voltage specifications had solid reasons.... including the fact that the older caps had a 10% over voltage tolerance that could safely be pushed to 15% while the new cap's technology really MEANS 10 % and not 11%. While normal operating conditions may be nominal, there are incoming spikes in the power, and also fault conditions that would be tolerated rather than experiencing cascade failure at the price of a few pennies. For the effort of installing them they are cheap insurance.

Were the other caps you used UPW's?? How about posting the numbers of the caps you substituted.

The replacement of electrolytic caps in the tuner will not affect the alignment as long as the adjustments are not touched. You may get lucky after deoxiting the power switching circuits going to the tuner and replacing the electrolytic caps.
 
Hello to all.I substituted the following caps so that the voltages would be exact.I read somewere that caps work best when they are at 80% of there required voltage.C15,16 330uf 25v #647-uhe1e331mpd. C20 1000uf 25v #647-uhe1e102mpd. C21 33uf 25v #647-upm1e330mdd. C22 100uf 16v #647-usf1c101mdd.I know the next size up in voltage caps would work, I'm a stickler for detail.My thanks to markthefixer & all other forum members that have chimmed in on this sx-1280 repair.This radio is for myself. I drives 4 bose 501 speakers in my pool room.It was such a thrill to get it up & running & sounding good for $30. in parts & several evenings of work.Now if I can get my FM going I'll be OK.Thanks again, tom south florida
 
Tuner board is accessible from above and below - are any of the chips getting hot to the touch?
 
tuner board update

Hello to all,Did a quick voltage check through out the tuner board.Got lots of hi voltage were it should be low & low voltage were it should be hi.Just for an example chip # PA1002 I have less then a volt at legs 10,12,13,14,15 they should be 6.4-6.9 v.Chip # PA1001-a I have zero volts atlegs 9,10,11,12,13,14,15,16. they should have been .2 - 3.6v. Chip #HA1197 I have 13v at all legs except 2,10,15. All solder joints look good, all wire wraps are good, no hot componets,probed the crap out of the board any ideas befor I recap & start unsoldering items to check.Thanks, tom
 
dognut said:
Hello to all,Did a quick voltage check through out the tuner board.Got lots of hi voltage were it should be low & low voltage were it should be hi.Just for an example chip # PA1002 I have less then a volt at legs 10,12,13,14,15 they should be 6.4-6.9 v.Chip # PA1001-a I have zero volts atlegs 9,10,11,12,13,14,15,16. they should have been .2 - 3.6v. Chip #HA1197 I have 13v at all legs except 2,10,15. All solder joints look good, all wire wraps are good, no hot componets,probed the crap out of the board any ideas befor I recap & start unsoldering items to check.Thanks, tom
Click to expand...


Did you verify that the various grounds are low impedance to chassis ground? Especially the chip's grounds. Not just 0 volts.

What chip was replaced on the tuner board?

Check the polarities of the electrolytic caps hooked up to the chips.

And there IS some FM sound? Do the meters work on FM? What about the stereo lamp?

You might want to replace the AM chip, ha1197, electronix.com has them for $0.99 ea.
 
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Hello,I love a quick reply.Looks like I've got some homework to do.I will go over the schmatic & start probing & measuring grounds. This might take a while. Will keep ya all updated.Thanks again, tom
 
OK a little more info.The only componet that looks to have been replaced at some time is the CHIP # ha11225. The fm does work however reception is very poor & the few stations that do come in sound better when the tuning meter needle is off to the side.No stereo lite ( I don't think the signel would be strong enought to fire it off) All the solder joints & componets look untouched except for that HS11225 chip. Going to check hard grounds that do not have caps in the circut, I am not an hi-fi tech but I know at work if I had a controls board that had several problems I would look for a common item.NO ground/grounds sounds good.Hi voltage would be another but I repaired that problem & the voltage was never hi.Will keep ya posted.Again,without the help from AK forum members I'd be lost scratching my head.Thanks, tom
 
Ok, I guess that ha11225 replaced the pa3001 chip.

It sound like alignment when it receives off center.

You have the manual? If not get it, and go to the alignment instructions.

I normally don't advocate this, but you can hardly make it worse, and may make it better, and you have displayed skills sufficient to the task.

You will need plastic alignment tools, with an undercut on the shaft because there are dual cores in the transformer and you need to adjust the cores (bottom) independently.

http://www.action-electronics.com/alignmenttools.htm
GC-9091 $1.50 1 Alignment Tool
GC-9338 $1.33 1 Burnishing Tool
GC-AS-5007 $10.15 1 Alignment Tool Kit
this is my kit^^^^

Step 8 of the procedure adjusts T6's bottom core ON DEAD AIR (disconnect the antenna and find a really quiet spot on the dial) to center the tuning meter.

Then tune to a weak station and try to adjust T6 for minimum distortion. You'll have a better chance detecting distortion by ear with a talk or classical music station, rather than rock etc...

Go back to the dead air point and readjust the lower core for centering.

Then do the minimum distortion point adjust again, then repeating the centering adjustment upon dead air until the minimum distortion point doesn't change after the centering adjustment either doesn't change or changes minimally.

Then you could go back ON THE WEAK STATION and try to peak the signal strength adjusting tc1, tc2 and tc3. They may be ok after T6 is adjusted correctly so test reception all over the dial and post here before tweaking them and maybe making things worse. The tc1,2,3 adjustments when done wrong could skew your sensitivity towards the top or bottom of the dial at the expense of the other.
 
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OK I was hoping you would chime in.I checked the hard grounds on the chips & circut board, all ok.Even found were the factory moved the ground from the power supply board.Leg 24 to 17.Going to order aline tools & give that a try.I've been reading the manual trying to figure out if I could tweek the pots without a scope or genorator.I'll place some whitness marks so if I need to I can go back.Once again thank you for the tip.Tom south florida
 
Well I spent the evening tweeking the tuner alinement pots with no success.Couldn't get rid of the distortion. T-6 lower & upper cores did work.I chased both meter needles around.Still can't figure why voltages are all wrong on all chips but the HA1197 & PA1001 are way-way off.. So am going to recap the board & replace the chips.I ordered the caps & am chip from mouser & am still looking for the PA 1001 & PA1002 chips.If anyone knows who has them please let me know.I'll keep ya all posted, tom
 
I just bought a SX-980 Tuner board that gave me all of the chips that I needed to get my SX-1280 up and running,the 980 seems to be a little easier to find.
I thought that I only needed PA1002A but I ended up needing them all so you might want to try to find a donor tuner board.
I havent read this post thoughly but you mention get your voltages right,my power supply failed and sent 19+ volts to all of the chips that normally recieve 13 volts so there was alot more damge then I thought.
I have it working but it isnt perfect yet.
Steve
dognut said:
Well I spent the evening tweeking the tuner alinement pots with no success.Couldn't get rid of the distortion. T-6 lower & upper cores did work.I chased both meter needles around.Still can't figure why voltages are all wrong on all chips but the HA1197 & PA1001 are way-way off.. So am going to recap the board & replace the chips.I ordered the caps & am chip from mouser & am still looking for the PA 1001 & PA1002 chips.If anyone knows who has them please let me know.I'll keep ya all posted, tom
Click to expand...
 
Hey steve,your postings was one of the ones I followed.I allready ordered & am going to recap,& replace the3001 &1197 chips mouser had all of it.I allso picked up a sx 890 on fleebay cheep & working.I am awaiting shipment of it.If its not to nice I will rob the chips out of it otherwise I am still looking for the PA1001 & PA1002 chips.At sometime in the past I downloaded a hi-resulution schmetic & printed it up to road map size so I could follow all the circuts.The chips have hi voltage were it should be low & low voltage or no voltage were it should be hi. Best I can figure is the chips got fryed.I probed & checked the crap out of this board.I'm at the point now were I'm going to remove it & simi rebuild it.My tunner board basically has the same problems as yours did.Thanks for the input.I appreciate everyones input.I have followed all the repair stories on this site & the diyaudio site & with my somewhat limited knowledge of hi-fi stuff have been able to make repairs.Thanks, tom
 
Actually at this point, you really should send it to someone who does tuners and has the equipment. A bad alignment on the front end is probably the culprit. Or then something REALLY strange.

Usually when it's messed up enough to require new chips it won't receive at all.
Re-capping first is certainly worthwhile, but with certain exceptions the electrolytic caps are not involved in reception issues and adjustments that manifest in the signal strength and tuning meters. Audio coupling OUT of the chips, yes, but not the meters.

The AM chip replacement is forgiving enough for you to fool with it and the adjustments to get something out of it.
 
Hello to all.Finshed recaping the tuner board & replaced the AM & pa3001 chips.Mouser had all in stock.My tuner works!!!!!!! am is noisy & buzzy but works.Meter does not peg its self any more on am.FM works allmost ok.Voltages on the new chips are were they should be.The 2 remaining chips still have wrong voltages so I gess untill I find thoes 2 My fm is so-so.I tryed tweeking the pots & the t6 upper & lower still chases me around.The lower centers the meter but the upper hardly does anything.I spent an hour looking over the schmetic & just realized that T6,vr2,vr1 talk to PA3001 chip.So tomarrow Im going to drive up vr2 & maybe i'll get some responce from t6.I'll keep ya posted when I get the other chips in. Tom
 
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