Sansui 5050 problem

[kwaichang]

Picked up a pretty good-looking Sansui 5050 at Goodwill for $30.00. Lights
went on but no sound. The F604 and F605 fuses on the F-2701 board were
blown. The blown fuses were 1/16A but the board says 0.15A. To be safe
I replaced with 1/16A fuses. The relay clicked, and I got very loud static for
about a minute. The static stayed loud when I turned down the volume.
After a minute one of the 1/16A fuses blew and now no sound again, and no
relay click.

Any suggestions on where to start?

Many thanks for any help!

 

[Bob]

that fuse is way too small. download service manual from hifiengine.

hope you can read a schematic and follow some simple rules for troubleshooting.

build a dim bulb tester and always use this when troubleshooting and always after a
test fix.

start measuring voltages in/around the power supply. then check voltages in
the protection circuitry and the output section.

 

[kwaichang]

that fuse is way too small. download service manual from hifiengine.

hope you can read a schematic and follow some simple rules for troubleshooting.

build a dim bulb tester and always use this when troubleshooting and always after a
test fix.

start measuring voltages in/around the power supply. then check voltages in
the protection circuitry and the output section.

Thank you Bob. The hifi engine schematic says f604 and f605 fuses are 0.15A.
I'll order some and build a dim bulb tester in the meantime. Any idea about
the purpose of those small fuses, or what could make them blow?

 

[avionic]

. Any idea about
the purpose of those small fuses, or what could make them blow?

Circuit over current protection.
To much current for that little fuse.
1/16th A = .0625 A or 62.5 milliamp
Recommended fuse is .15A = 150milliamp

 

[Bob]

on the 2648 board, there are 3 fuses, F601, 602, 603 which are 2A, 4A, 4A.

I cannot "see" your referenced fuses. perhaps post a screen shot.

in any case, the blown fuse is protecting something if it blows, hence a short
somewhere in the circuit power is being fed through the fuses.

 

[Bob]

@avionic great catch - usually I assume others read better than myself.

or in this case, it may be just enough underpowered. I had a Hafler that used 1/16 A
and blew a few times til I upped it to 1/10.

 

[kwaichang]

@avionic great catch - usually I assume others read better than myself.

or in this case, it may be just enough underpowered. I had a Hafler that used 1/16 A
and blew a few times til I upped it to 1/10.

Thanks for all the helpful replies. I've attached a picture of the F-2701 board. Fuses
F604 and F605 that blew are next to each other in the middle. At the two
red arrows the board has dark spots around the capacitors. Leak or just some
dirty hot glue?

In the second picture with one red arrow the capacitor is bulged up a little and
looks suspicious to me, but I don't have much experience. Is the capacitor bad?

 

[Bob]

could you point to where the f604/5 fuses are - on the schematic. or post screen-clip
of the section where these fuses are.

time for a full recap. caps can look "bad" and still work. caps that look good
can test good or bad. can't/shouldn't judge based on looks.

no telling if you get past the fuses, whether there aren't more problems.

build the DBT first, plop correct rated fuses in, check F601-3 also.

 

[kwaichang]

could you point to where the f604/5 fuses are - on the schematic. or post screen-clip
of the section where these fuses are.

time for a full recap. caps can look "bad" and still work. caps that look good
can test good or bad. can't/shouldn't judge based on looks.

no telling if you get past the fuses, whether there aren't more problems.

build the DBT first, plop correct rated fuses in, check F601-3 also.

Thanks again Bob. Here's the schematic with of the 5050 with the F-2701 board.
Hope it's readable. Fuse F-604 (0.15A) is top middle of the F-2701 block.
Fuses F601, F602, F603 are all OK.

Never done it before, but I think I'll take your advice and try a recap.

 

[Bob]

the right .15a fuse seems to come from the right diode bridge next to large label 10d-2.

roll up your sleeves and start the troubleshooting. suggest you build DBT, add correct fuses
(assuming they blew because they were underrated) and trace the voltages and mark
them on the schematic as you follow the voltages.

the goal is to make sure there's no shorts downstream from where you start, then ensuring
the various components are correct (resistor values, cap values in range, transistors etc).

suggest cheap mega 328 or equivalent tester (under $10) or DMM/VOM with diode/transistor
tester, cap tester, in addition to resistor and voltage tests.

Bob