Marantz SR-7400 ps repair

[fixxxxxer]

Hello everyone, i have a marantz sr-7400 avr. The main filter caps have to be changed, one of them is very close to explode. The original caps are samyoung brand 71V,18000uf and 85 degrees

The service manual says transformer secondaries are 41VAC, and the dc voltage seems +-55V. Now, i have two pairs of nippon chemi-con caps rated at 22000uf/63V. They were extracted from pioneer elite series avr's and really good quality. Can i use them with 55VDC safely?

If we consider the worst, 41VAC*1.41 = 58VDC (without any diode loss) and if the voltage on the wall outlet rises a little, it will probably hardly hit 60VDC. In these conditions, is it safe to use these 22000uF, 63V, 85 degree caps?

[!]

Yes, it is safe to use those caps assuming your power grid is relatively stable. If the grid is not relatively stable it is your gamble to make, or you could put a surge protection circuit before the amp.

[Mooly]

Absolutely fine... no problems whatsover with the voltage.

[fixxxxxer]

Seems OK, thanks for the answers very much.

@ "!" where should i put the surge protection? between the ps circuit and the amp circuit? or between the wall outlet and the amplifier ac inlet?

[!]

^ In theory either would work, but in practice between the wall outlet and AC inlet (or after AC inlet and before transformer) is much more practical because the relative difference in peak voltage is higher, and because this is a common use to which surge protection devices or discrete components are designed for and common, easy to find.

Note that many inexpensive surge strips are designed only to deal with voltage significantly above the level it would take at input to the PSU to cause excessive capacitor voltage. For example I see in Turkey your AC mains voltage is 230VAC? Is that the input voltage rating for the transformer?

If so, the surge protection circuit should ideally handle as low as 270VAC as that would put your 55VDC up around 65VDC. Normally people do not worry about such things as it is accepted that AC voltage has to remain stable for equipment not to be damaged, my comment was only pertaining to the issue that you have less voltage margin "IF" such conditions exist at your location.

[fixxxxxer]

Caps changed, not any problems so far, thanks for the advices! The main rails never exceed +-50VDC with a 220V wall outlet as measured during the maintenance process, datasheet says 55VDC on them bu its probably with 230V or 240V (max) wall outlet. So for now, it seems to be better than original, thanks again everyone a lot.

[Mooly]

Thanks for the update...