Hi there, I'm working on the 25W amp board of a Yamaha YST-MS25. It's 20yrs old.
Since a few months the volume on the left channel is way too low. It turned out that - compared to the intended use and the former price tag of this thing - they put solid stuff into it. So I decided it's worth a recap.
The board uses two amp ICs on opposite sites of the board. Both ICs are connected to the same heatsink. The heatsink unfortunately is a bridge-like construction that covers almost all other components, including the majority of the caps (pictures and schematics below).
All 30+ electrolytics were Nichicon VX, old radial series, general purpose, 85°C, now out of production. Most of them measured ok.
The two 470 uF on the satellite outputs (C20 in H3, C41 in J4) both had only 420 uF. Maybe they came like that from the factory.
Some of the 10 uF/16 V had an ESR 2.5 times higher than other 10 uF/16 V. They are probably dry.
I'm going to replace all electrolytics with Panasonic FC. Unfortunately Panasonic and others stopped production of very small values for some variants. Currently smallest FC is 2.2 uF. But smaller ones are required as well.
As 1uF I can get my hands on Panasonic NHG, Chemi-Con KMG or Rubycon PX.
For the 0.22uF ones I couldn't get hold of anything suitable, only found crap caps or old stock that's out of production since years and sold at exorbitant boutique prices.
Four 0.22uF electrolytics are in the Yamaha schematics, red circles:
C24: sub amp IC6/LA4485 (runs in bridge mode) channel 1 input capacitor
C30: sub amp IC6/LA4485 unused channel 2 to ground
C39: sat amp IC5/LA4613 standby supply capacitor
C40: sub amp IC6/LA4485 standby supply capacitor
According to the LA4485/LA4613 datasheets increasing these caps isn't a good idea. So I'd like to keep them at 0.22uF.
Should it / is it possible to replace these 0.22uF electrolytics with another type, like ceramics or <...>? If so, which ones?
The LA4485/LA4613 datasheets do not mention any cap types, however, in all example circuit drawings they used the sign for polarized caps.
Since a few months the volume on the left channel is way too low. It turned out that - compared to the intended use and the former price tag of this thing - they put solid stuff into it. So I decided it's worth a recap.
The board uses two amp ICs on opposite sites of the board. Both ICs are connected to the same heatsink. The heatsink unfortunately is a bridge-like construction that covers almost all other components, including the majority of the caps (pictures and schematics below).
All 30+ electrolytics were Nichicon VX, old radial series, general purpose, 85°C, now out of production. Most of them measured ok.
The two 470 uF on the satellite outputs (C20 in H3, C41 in J4) both had only 420 uF. Maybe they came like that from the factory.
Some of the 10 uF/16 V had an ESR 2.5 times higher than other 10 uF/16 V. They are probably dry.
I'm going to replace all electrolytics with Panasonic FC. Unfortunately Panasonic and others stopped production of very small values for some variants. Currently smallest FC is 2.2 uF. But smaller ones are required as well.
As 1uF I can get my hands on Panasonic NHG, Chemi-Con KMG or Rubycon PX.
For the 0.22uF ones I couldn't get hold of anything suitable, only found crap caps or old stock that's out of production since years and sold at exorbitant boutique prices.
Four 0.22uF electrolytics are in the Yamaha schematics, red circles:
C24: sub amp IC6/LA4485 (runs in bridge mode) channel 1 input capacitor
C30: sub amp IC6/LA4485 unused channel 2 to ground
C39: sat amp IC5/LA4613 standby supply capacitor
C40: sub amp IC6/LA4485 standby supply capacitor
According to the LA4485/LA4613 datasheets increasing these caps isn't a good idea. So I'd like to keep them at 0.22uF.
Should it / is it possible to replace these 0.22uF electrolytics with another type, like ceramics or <...>? If so, which ones?
The LA4485/LA4613 datasheets do not mention any cap types, however, in all example circuit drawings they used the sign for polarized caps.
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