Sherwood RV-5030R VAPORIZING mains fuse

Bassblaster

Super Member
i got a Sherwood RV-5030R AV receiver from the mid 90's from a friend he wants repaired, ive had it for 3 months because i broke my hand about 2 months ago but im good now so today i pulled it back out and done some tests. its a 5 channel unit with all discrete outputs. i cant find a service manual for it so i cant get to crazy with it. i pulled and tested every output transistor and they all tested good. i pulled the 6A rectifier diodes, all fine, pulled the 4 1N4007's for the standby circuit and they tested fine. even tested some other random diodes in the power supply part and everything has been fine. so i am completely lost of what keeps blowing the main 5A fuse. there's no solder bridges on anything. the only thing i haven't tested are the emitter resistors, drivers and some (Zener??) diodes around the amplifier. right now i have the 4 regulators from the power supply pulled, 2x 7806, 1 7815 and 1 7915. i cant think of anything else that can draw that kind of current without burning up.
any thoughts? Need pics of anything just post.
 
I don't know where you were searching but manualscenter.com say they have a service manual for $4.99
 
ok ill pull the filter caps and the smaller caps in the power supply, how do i test a cap for shorts? i dont have an ESR meter if thats how.
 
check they have drained first by seeing if voltage left in them .then test ohms with your meter . do it both ways .
 
with the main filters (2x 8200uF 63V) with both caps measuring ohms both ways they impedance started low then would slowly climb up. I let them get to 13K before i let go. there "Samhwa" brand. never heard of it
 
probably ok then ..
where are you up to now ?
am guessing rectifiers are removed ? if so does fuse still blow ? if it does blow ohm out the transformer .
 
probably ok then ..
where are you up to now ?
am guessing rectifiers are removed ? if so does fuse still blow ? if it does blow ohm out the transformer .
right now im pulling the smaller caps in the power supply. rectifier is still out. thing is...it blew all my 5A fuses so ill need to get some more (obviously). when its plugged in i get the red standby light, but when you power it on thats when the fuse disappears.
 
i know. imma see if i can buy the one on manualscenter.com.
i pulled the standby transformer and marked the readings.
upload_2017-1-14_19-1-31.png


Now with the main transformer...where do i begin
IMAG0450[1].jpg IMAG0451[1].jpg
that single yellow wire has a single black with but its attached to the PCB and not the transformer. i do know the black and blue is the AC in because it connects to the power cord on the board.
EDIT: The standby tranny the middle pin marked ? is also no connection. the board is just a pad for it.
 
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start with plugging in mains supply to transformer . then standby circuit .obviously needs this to switch on . hopefully fuse doesn't blow at this point . if it does the schematic needs to be seen sooner than later .
i can only assume at this point the standby circuit is fairly typical .
 
about that...im out of 5A fuses. it ate the 2 i had. the only fuses i have in that size are 500mA. but they came from china so i doubt there even 500mA. i could order some more from mouser or try some non chinese bay fuses.
 
I wouldn't spend too much time on that unit. Nothing personal, but the time and effort you already have into it likely exceeds its value.
 
I wouldn't spend too much time on that unit. Nothing personal, but the time and effort you already have into it likely exceeds its value.
ive only spent about $2 on it, and i haven't put too much time into it either. only a few hours. i think its worth a little more than that. 80W into 5 channels with 15000 inputs? if it were mine i would like to have it running with specs like that
 
A shop would probably charge $50-60 just to look at it, and then maybe $75/hour, give or take, to work on it. Plus parts.

One in working order recently sold on Ebay for $60, shipped.

Obviously it's your call to continue but...
 
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i know what shops cost. and there's also no shops within 100 miles of where i live. im not a shop i just do this in my bedroom. i work on all my own gear
 
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but what am i going to about the empty slot for the 5A fuse? It won't be doing much without it

Just put a fuse back in it. The DBT helps prevent the fuse from blowing as all the current from a short will be going through the lightbulb.
 
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