My Revox B790 has blown its fuse

csrote · 16th September 2008, 08:41 PM

Fuse is 400ma @ 120v or 200ma @ 240v. It is not available at Radio Shack (closest is 500ma@240v) so I will need to do an actual parts order from a major parts house (was going to do any way for other projects.)

I have the service manual.

A blown fuse implies power supply problems. Any tips on trouble shooting the PS when I finally get the proper fuse?

Thnx for all help,
Cliff

rayfutrell · 18th September 2008, 02:02 PM

In the US you want the 400ma 120V fuse. Home Depot has some of those European fuses, so you might find it there in the electrial parts. I have seen fuses open for no apparent reason except old age.

The 500ma 250V fuse will work, but the current rating is 25% too high.

Regards,
Ray

SaSi · 18th September 2008, 03:17 PM

IIRC, the fuse in the Revox TTs is a slow blow one. I've replaced the original one with a slightly overrated quick blow one, but overrated by 100mA only.

One of the most simple reasons why the fuse might blow is that the decoupling capacitor that is soldered on the mini PCB where all the AC power cables concentrate is short. Inspect it closely and you might find it has turn black or even broken at one side.

You could also remove that PCB from the base and check the resistance across the capacitor's leads. If it is 0, then it is probably dead.

Steerpike · 18th September 2008, 05:49 PM

Since it's a ReVox, my bet is one of the three large electrolytic capacitors on the power supply PCB has gone short circuit.
Those Frako ones are almost guaranteed to go short after 30 years, so you might want to replace them anyway while you're ordering parts.

16th September 2008, 08:41 PM	#1
csrote diyAudio Member Join Date: Jun 2008	My Revox B790 has blown its fuse Fuse is 400ma @ 120v or 200ma @ 240v. It is not available at Radio Shack (closest is 500ma@240v) so I will need to do an actual parts order from a major parts house (was going to do any way for other projects.) I have the service manual. A blown fuse implies power supply problems. Any tips on trouble shooting the PS when I finally get the proper fuse? Thnx for all help, Cliff

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18th September 2008, 02:02 PM	#2
rayfutrell diyAudio Member Join Date: Sep 2004 Location: virginia	In the US you want the 400ma 120V fuse. Home Depot has some of those European fuses, so you might find it there in the electrial parts. I have seen fuses open for no apparent reason except old age. The 500ma 250V fuse will work, but the current rating is 25% too high. Regards, Ray

18th September 2008, 03:17 PM	#3
SaSi diyAudio Member Join Date: May 2008	IIRC, the fuse in the Revox TTs is a slow blow one. I've replaced the original one with a slightly overrated quick blow one, but overrated by 100mA only. One of the most simple reasons why the fuse might blow is that the decoupling capacitor that is soldered on the mini PCB where all the AC power cables concentrate is short. Inspect it closely and you might find it has turn black or even broken at one side. You could also remove that PCB from the base and check the resistance across the capacitor's leads. If it is 0, then it is probably dead.

18th September 2008, 05:49 PM	#4
Steerpike diyAudio Member Join Date: Jan 2006 Location: Johannesburg, South Africa	Since it's a ReVox, my bet is one of the three large electrolytic capacitors on the power supply PCB has gone short circuit. Those Frako ones are almost guaranteed to go short after 30 years, so you might want to replace them anyway while you're ordering parts.

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