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7704A fuse has blown

 

Hello


I have a 7704A which had been stored for quite a while¡­


it worked ok for 10mn and then one of the two fuse went off.


i'm not sure whether it is the fuse for the line circuit or inverter.


The schematic for the 7704A seems hard to find. Would anyone know where i can find it or kindly send the relevant part for the switched mode power supply? I'm new on the 7704A !


Kind Regards


Thierry.
 

Thierry,
Try ko4bb.com.
--John Gord
 

Hi,

You can start by testing the bridge rectifier for a shorted leg. The electrolytic capacitors are always suspect but you usually have click mode on those. Google Tektronix 7704a manual for a list of sources. You should be able to get a free one.



Jerry Massengale

-----Original Message-----
From: thierry.delaitre@... [TekScopes] <TekScopes@...>
To: TekScopes <TekScopes@...>
Sent: Sat, Sep 27, 2014 12:31 pm
Subject: [TekScopes] 7704A fuse has blown






Hello


I have a 7704A which had been stored for quite a while¡­


it worked ok for 10mn and then one of the two fuse went off.


i'm not sure whether it is the fuse for the line circuit or inverter.


The schematic for the 7704A seems hard to find. Would anyone know where i can find it or kindly send the relevant part for the switched mode power supply? I'm new on the 7704A !


Kind Regards


Thierry.

[Non-text portions of this message have been removed]








[Non-text portions of this message have been removed]
 

thanks John/Jerry

Yep found the schematics at


I only checked the A4 file earlier. the schematic is actually in the A3 file.


It is the 4 amp fuse which has blown up. The 2A fuse is ok so most likely to be the bridge rectifier and/or the 550uF caps. Will check.


Thanks


Thierry.
 

Check to make sure that the fuse that blew is the correct type of fuse.
I have a 7934 that arrive with a similar problem. When I finally thought
to check the fuse type, I found that it was incorrect. Installing the
correct fuse fixed the problem.

DaveD

On 9/27/2014 11:31 AM, thierry.delaitre@... [TekScopes] wrote:

Hello


I have a 7704A which had been stored for quite a while¡­


it worked ok for 10mn and then one of the two fuse went off.


i'm not sure whether it is the fuse for the line circuit or inverter.


The schematic for the 7704A seems hard to find. Would anyone know
where i can find it or kindly send the relevant part for the switched
mode power supply? I'm new on the 7704A !


Kind Regards


Thierry.

[Non-text portions of this message have been removed]
 

Thanks.

One of the diode on the bridge rectifier looks shorted by measuring it (while soldered on PCB).


Would any 600V / 8A bridge rectifier do as a replacement or can i go with something with lower spec?


I'll also check the 550uF capacitors.


Thierry.
 

Yes, definitely check the big caps. I had a 7904 with one or two diodes in the bridge shorted, and one of the big caps shorted - usually those fail open with age and abuse. I don't know which went first. Ed

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