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Lights dimming after recap?

darkhosis

darkhosis

Active Member
My Technics SA-5370 project was going along well. Ordered new filter caps (10000uf 80v) and replaced most of the electrolytics in the power drive amp and regulator. I got the wrong kind (22 instead of 2.2 and didn't see the bipolar type cap) for the DC detector so I had to leave those alone.

Fire it up, and the receiver sounds great. Im new at this so I've triple checked my work and felt good that the receiver is working. But..

I can't turn the volume past 3 without the bass and then higher volumes starting to dim the lights and then the speaker protection kicks in.

I don't get it, the Technics SA-5370 specs say its 48 watts per channel, and my Sansui 771 is 32 watts per channel and can easily drive larger speakers louder.

Not sure what to do.
 
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This isn't my realm so take my advice with a grain of salt. That said, assuming you got values right. I'd suspect a polarity issue on a cap. I hope you noted orientation on removal because sometimes (often ) the silkscreening labels have errors. Other thought solder bridge. Did you test with DBT when you powered on? Good luck with the project.
 
nj pheonix said:
This isn't my realm so take my advice with a grain of salt. That said, assuming you got values right. I'd suspect a polarity issue on a cap. I hope you noted orientation on removal because sometimes (often ) the silkscreening labels have errors. Other thought solder bridge. Did you test with DBT when you powered on? Good luck with the project.
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Along this line, noting what values were actually installed vs. what is shown on a schematic. Afaik, if there is no reason to believe there was any other previous work and generally it was working OK before, the installed values take precedent over schematic.
 
nj pheonix said:
This isn't my realm so take my advice with a grain of salt. That said, assuming you got values right. I'd suspect a polarity issue on a cap. I hope you noted orientation on removal because sometimes (often ) the silkscreening labels have errors. Other thought solder bridge. Did you test with DBT when you powered on? Good luck with the project.
Click to expand...
This I have seem many times.

petehall347 said:
have you got the service manual ?
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And the SM are not 100% correct.

I HOPE you did take pictures of the boards....I have as to past Woops....It's the pictures that have saved me.
 
hello darkhosis. Checked Hifi engine, HiFi manuals. Both have the owners manual. The Hifi Engine manual I looked at has the schematic at the end of the manual. Possible check to see if dc voltage is at the output kicking in the protection mode. No speakers connected. Voltmeter across the speaker terminals. DC voltage should be in mv. Not sure what's pulling down the power supply of the unit.
 
sounds like a cap in backwards to me .. if it is that i would expect it to be getting very hot and likely to blow itself apart ..
are the main filters supposed to be 10.000uf ?
 
What speakers are you driving?
You mention the Sansui 771 is 32 watts per channel and can easily drive larger speakers louder.
Are these the same speakers that the Technics are using?
 
something like c903 in backwards would very likely cause this scenario .
saying that said you didn't touch this board so forget that one ..
 
I do have a schematic I'm working with. And I did take a pic, though.. there's ONE that I pulled before I took the photo. But the capacitors were all orientated the same way, I think as to keep whoever was assembling it less confused.

The 30v (correct) from the output of the transformer is measuring on the capacitors, it drops pretty rapidly when I turn up the volume of the speakers. Like about 3 and I'm losing 5-6 v DC across both caps to 24v DC.

I measured the DC from the speaker terminals with the Aux and volume down to 0 (with speakers connected btw) and the left channel was around 9mV the right was even lower.

The main filters originally were 10k uf 45 v, the new ones are 10k 80v

I will check again for orientation
 
goat67 said:
What speakers are you driving?
You mention the Sansui 771 is 32 watts per channel and can easily drive larger speakers louder.
Are these the same speakers that the Technics are using?
Click to expand...
I bought 2 NLA from a guy and he threw in his old receiver for free. I haven't hooked them up, I've been using a pair of Advent/4 and then last night I tried a couple of Polk t15

Forgot to mention. With the Sansui I 've got Dynaco A25, a pair of OLA and whatever else I'm auditioning. Right now NSM Segue monitors
 
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This is one case where I don't mind looking like a noob if it means my recap wasn't the issue. Now I can't wait to get back and try it tonite. Thank you!!
 
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