IMG STA-160 - trouble again...

[gruni]

Hi everybody!
I have an IMG StageLine STA-160 amplifier. It has been working perfectly for about two years. Today it blew the 630mA fuses feeding the +/-24, +/-15 and +8V raisl through the 18V-0-18V windings of the transformer. I found out that only the right channel causes the fuses to blow so the protection and input circuits should be okay. I don't see any connections between the high power part of the right channel and the low power circuits that could be responsible for blowing the fuses except for CLIP, INPUT and +24V but all of them are at normal levels. The PSU-Fault checking circuit does not seem to have caused any problems as the fuse doesnt blow with the power amp section disconnected from the PSU-PCB (the PSU-Fault circuit is located between the power amp fuses and the connection cables from the fuses to the power amp.

Schematics for the amp can be found at schematicsunlimited (.co.uk)

Hope you can help me!
Thanks

 

[gruni]

i'm still clueless. i just cant find anything wrong. the fuse keeps blowing... i should add that the power amp fuses are ok so the power amp section should be working too

 

[singa]

Hi, The 630mA fuse that blew already gives you the clue to that section.
Please provide a link to the schematic ,that's the least you should do
if you want members to help.

 

[gruni]

i already provided a website where you can download the schematic as i dont know if i'm allowed to link to the schematic directly.

anyways i uploaded the relevant parts as an attachment to this post!

 

[gruni]

the other channel works perfectly, by the way

 

[gruni]

seems as if the fuses i tested were just weak because of their age. i replaced the fuses once again and now everything works again. strange...

 

[singa]

seems as if the fuses i tested were just weak because of their age. i replaced the fuses once again and now everything works again. strange...

Hi, It could be the turn on surges ,you can substitute same rating slow blow
fuses for the fast blow ones.

 

[gruni]

i thought of that, too. the strange thing is that it kept blowing the fuses for 4 tries and now it suddenly just works again...