Hello, first time to the forum. My Pioneer SX-1250 power supply assembly (AWR-107) is registering higher than normal voltages which I think might be affecting the stabilizer board. The 85v is reading 92.6v, the -87.5v is measuring -94.0v and the 23v is measuring 26.24v. Is this from the transformer or are some of the diodes on the board to blame ? Any help is appreciated.
SX-1250 Power Supply Assembly Voltages High
- Thread starter NetSonny
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What is your AC line voltage? That will tell the story. These unregulated supplies are a result of transforming/rectifying/filtering the AC line and the voltages on the schematic represent only one line input voltage, IIRC 115V. Line is allowed be approx +10 -15% of 120V. If it is outside this range time to look into that.
On the big schematic it shows input 120VAC and you are below that, but the unreg voltages are higher than what the schematic shows.
So I assume the power amp supply voltages are higher than published +/-70V?
To be honest it should not be a problem, if the regulated voltages are correct and the units is operating correctly.
So I assume the power amp supply voltages are higher than published +/-70V?
Some voltages are off so need to supply all the measurements &/or you need to rebuild your power supply.
but wait
If +5.4V is off (9.16V) then I assume +13.5V is high too. +5.4V is derived from +13.5V so could be a problem as it could smoke the ic's in the tuner = eek = fix immediately and do not power up again until fixed. Those ic's are not to see much more than 16V IIRC.
Enjoy your turkey and holidays, that is the bird is what's on the menu.
but wait
If +5.4V is off (9.16V) then I assume +13.5V is high too. +5.4V is derived from +13.5V so could be a problem as it could smoke the ic's in the tuner = eek = fix immediately and do not power up again until fixed. Those ic's are not to see much more than 16V IIRC.
Enjoy your turkey and holidays, that is the bird is what's on the menu.
petehall347
the brandy coffee man
post all voltages ..regulated and unregulated ..
i suspect its ready to rebuild as most are by now ..
i suspect its ready to rebuild as most are by now ..
The unit is set for 120vac. I am in the middle of a rebuild. Actually replaced all caps, many transistors and diodes on various boards. Had a couple of stabistors (STV-H3) that had the arms fractured off. Decided to make my own (mistake) as I used a common epoxy to encase the diodes. Finals ran away and fried the stabilizer resistors and transistors. I rebuilt the stabilizer board this evening with new components. My concern is that the voltage applied to the rectifier on the stabilizer board are too high. Is there a possibility that the transformer sustained some damage to the windings and is allowing for a higher output voltage ? As soon as I double check the diodes on the power board, I will check all voltages and respond. Learning as I plug along....
transformer damage is highly unlikely.
voltage measurements inside of the regulator will tell the tale. zener voltages are paramount.
German eBayer has STV-3H diodes (NEW!! at a very reasonable price.) Cracked arms call for thin washers, NOT DIY diodes.
AWR-107 voltage WILL BE HIGHER without the expected loading. Missing amp board draw are missing loads, and thus higher voltages - we call them UNREGULATED voltages for a reason: they VARY with the loading.
voltage measurements inside of the regulator will tell the tale. zener voltages are paramount.
German eBayer has STV-3H diodes (NEW!! at a very reasonable price.) Cracked arms call for thin washers, NOT DIY diodes.
AWR-107 voltage WILL BE HIGHER without the expected loading. Missing amp board draw are missing loads, and thus higher voltages - we call them UNREGULATED voltages for a reason: they VARY with the loading.
BobbyN
Well-Known Member
Someone said do not power up until problem found. Can't argue that one. I would check all parts associated with that 13.5 volt supply since you are almost double the 5.4 volts on pin 8. The light/lamp load on that 5.4 volt circuit is about 1.2 amps. I do know that C13 is a 25 volt cap which is right on the edge at that point. I personally had Q12 go bad there and have read in the past that I'm not the only one.
Your meter is correct when reading 119.3 volts mains, right?
Someone also above mentioned the mains voltage. Just for reference, when running my 1250 on a variac at 115 volts, ALL the voltages are less than at full main voltage, which at my house is 123V.
Bob
Your meter is correct when reading 119.3 volts mains, right?
Someone also above mentioned the mains voltage. Just for reference, when running my 1250 on a variac at 115 volts, ALL the voltages are less than at full main voltage, which at my house is 123V.
Bob
Thanks WE6C, I haven't repowered yet. I am waiting for fiberglass insulators for the STV-3H leads. The old insulators are beyond re-use. I still have to replace the power transistors on the left amplifier board as well as the stabistors ( NEAT DESIGNATION) . I do think that markthefixer is correct in his statement that I should have "loaded" the main power and stabilizer before measuring "regulated" voltages. Only makes sense. It ran before I added my newly-made STV-3H s, then I burnt resistors on the amplifier board. I can guess wherein lies the problem..... Thanks for your input. P.S. : Replaced both Q12 and Q13....hoping for the best.
mtf means that if the stabilzer sees no load the unregulated input will peak which is what you are experiencing
You should have explained exactly what you were up to in the first part of the thread, rather than asking a loaded ? "why the unregulated is higher than normal"
You should have explained exactly what you were up to in the first part of the thread, rather than asking a loaded ? "why the unregulated is higher than normal"
petehall347
the brandy coffee man
please hold back before proceeding . all we want is your amp is in working condition . its tried and tested already .. bit by bit will bite back . its all or nothing ..well worth it in the long run ..
BobbyN
Well-Known Member
Maybe the load isn't quite that much. I was thinking of the dial lamp circuit and this I believe is the "function" lamp circuit. I'll look again when I have access to the SM.
Bob