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Robyn SB-520 D blowing fuses?

S

Shawn1506

Member
Jan 14, 2013
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I recently hooked up my base radio with my A99 on the chimney. It has been years since I have even looked at this stuff so please bare with me. I Have been talking along on my radio with a good SWR of about 1.2 on channel 1 and about a 1.4 on channel 40 for about a week or so. Well the other night my buddy and I were talking and I decided to try out the LSB on the radio. I flipped the switch and listened and got him tuned in. I keyed the mic and as soon as i spoke, the 3 amp fuse blew in the back of my radio. I replaced the fuse with a 2.5 amp fast acting, so not to hurt the radio, then turned back to AM. Now every time I key up and speak on AM the fuse blows. Does anyone have any idea what this may be? The radio has had channels put in it about 30 years ago. but other then that this radio is stock and in very good shape. I thank you for your help in advance.

Shawn
 

Sounds like C179 has gone fault. It's a 2.2uf 25V blue tantalum capacitor located near the finals on the board, next to two white jumper wires. When this capacitor goes short, it can blow fuses per your description. Replace this capacitor with a 2.2uf 25V electrolytic capacitor, and that usually fixes the problem. Good luck!

~Cheers~
 
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I had a Cobra 139 XLR that did the very same thing. I replaced the part ExitThirteen spoke of and it worked..
 
Been working on a Navaho TRC-458 - which is a 858 PLL-based chassis like the Robyn and the Cobra 139XLR. Sure enough, checked C179 first and it was faulty. Replaced it with a new tantalum cap that is rated 2.2uf @ 25v instead of a 16v OEM part. Also had to replace a bias pot and cleaned the contacts in the relay with a piece of thin, clean cardboard and some contact cleaner. The relay socket also got cleaned.

Aligned it and now it works OK with the exception of some popping sounds when transmitting. Might need to have the AM regulator replaced next. Or end up re-capping the whole radio. Haven't found the cause of that fault yet.

If it keeps blowing fuses, then you might want to check/replace the power supply regulator and zener diodes - for a start. Could also be other shorted aluminum electrolytic caps . . .
 
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