Discussion in 'Exclusively Sansui' started by misterguitar, Apr 24, 2017.
hmm how is a "safety capacitor" defined. At least how would I find one on mouser or digikey's site?
Hi, for ''across the line'' in your application you will need an X2 rated safety film capacitor, if it was line to ground you would need a Y2 rated cap.
Here are just some examples.
You will have to look at the data sheets to confirm the X2 or Y2 rating.
This is great news I ordered an X2/Y2 cap listed as "safety film" from mouser. But now I understand what X2/Y2 means! Thanks so much for the reply!
more on safety caps if you care
Your welcome, all the best with it.
Ok. Got it all back together. No small feat! This unit was filthy when I got it. And washing it in isopropyl alcohol seemed to either melt off some kind of conformal coating or it really did have that much tar and nicotine on it! So this is what was done.
Main filter caps replaced with Nichicon KG 6800uf 63 volts
Power transistors replaced with on semi 21994/21993G
Replaced fuse resistors on Amp board with Xicom 6.8 ohm 1/4 watt metal film
Replaced all electrolytics on power/amp boards with identical value nichicon muse, fine gold, and Elna Silmic. 1uf caps replaced with WIMA 1uf 50volt stacked films.
Replaced the differential pairs with KSA992s. I am worried I did not get the right ones and they don't have enough gain. I measured the gain on the old ones vs the new ones and there was a big difference. Not sure what gain banding these should have?
Replaced all electrolytics with identical value elna SILMIC
Replaced tantalums with like value Elna Silmic
Repalced the orange caps with like value WIMA stacked films.
Replaced all electrolytics with identical value elna SILMIC, Nichicon FG
Replaced orange caps with like value stacked WIMA films
Just tried to fire it up and no relay click!
If it had not been so filthy and I didn't already have to take it apart to clean it I would have done this one section at a time to avoid the problems with a shotgun.
I guess the best place to start is at the power supply? And making sure the voltages are right? And pick apart the protection circuit to look for how it works and what may be preventing the relay from opening.
What were the gains of both your old and new parts? I normally use the KSA992FBU's and have no trouble with gain.
Yes you are on the right track here, power supplies first then try and check your dc offset pre the protection relay.
Hmm. I have KSA992FTA. Old ones about 500 hfe. new ones between 350 and 400. I'm
trying to decipher the coding for product name and hfe ranking on the data sheet vs what mouser has listed.
hmm 36 volts pre relay on one side..
Rail voltage should not be there!
FTA's and FBU's are both 300-600 hfe, one is just packed in ammo style and the other bulk. See how you go with them, l don't see them being a problem with slightly lower gain, if you have enough just pick the 4 highest evenly matched in pairs. If you are concerned about them maybe see if you can find the KSA992FBTA variant (430-600) or the KSA992E (400-800) although l don't think these are readily available.
Nah that is not so good, prob a good idea to recheck all of your new transistor leg orientations and possible solder bridges on that channel.
I checked all the cap polarities. All are fine. checked the Ksa992 orientation. They are correct. If I pull the board with the diff pair boom relays open as normal. No sound of course. Put it back in, no dice. Any way the alcohol bath may have messed up the power transformer?
trying to find the easiest way to get to where th bias is measured. the resistors are al jammed up in the heat sink right? the big ceramics. Id look at the schematic but my desktop hd died to ight. So i'm on the phone here. lol
no solder bridges or cold solders either.
hmm the schematic I have does not show voltages for anything. Usualy the would be ariund transistors or other items or at least I have seen them that way before. I'm trying to finda point to probe to look for correct power supply voltages. I'm going to
put the original transistors back for the diff pairs and see if I can get it to work.
ok put the old transistors back in. Still won't open the relay. . relay opens if I pull that board with the diff pair out. I would think if I can figure out what conditions cause the relay to ooen or close I coukd figure out what the peoblem is. Anybody know how these protection relay circuits work?
Ok so now I'm starting to wonder if I maybe got the power transistors in backards visa vi NPN PNP mixed up?
Ok! Now we are moving! Found. bad solder joint on the diff pair board. New solder and boom! Still some issues though. When hitting the audio muting button I get a super loud popping and crackling noise. This also happens when hitting the low filter button as well. Is there some kind of snubber cap on these? Or should I start looking at my work on the tone amp board?
And the phono amp is completely dead. But the radio and aux sound much improved!
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