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Sherwood RA-1140 stereo receiver

Discussion in 'Troubleshooting and Repair' started by rtripboy, Sep 3, 2016.

  1. rtripboy

    rtripboy

    2
    0
    Sep 3, 2016
    I bought this Sherwood sometime in the early 90s. I think I paid around $80 for it, so it's a fairly cheap unit. It has a digital quartz ppl tuner with an orange display. I discovered one day it would not power up. I checked the one replaceable fuse it has was blown. As far as I know, it failed while powered down. A power surge maybe. Anyway, I bought a new fuse and replaced the blown one. When I turned it on I got a very loud hum. Nothing was connected to it when I did this. I quickly unplugged it and have not plugged in back in. It did not emit the hum until I pressed the power switch. Am I right in assuming the amp is blown? Can it be repaired and is ti worth it for what was a cheap receiver even when it was new. The thing is: it actually sounds pretty good. Not much power, but sounds good.
     
  2. 73's de Edd

    73's de Edd

    2,678
    1,085
    Aug 21, 2015
    Sir rtripboy. . . . . . .

    PROCEDURALS:


    Confirm that the fuse replaced was the 5A unit in the RED box.
    That the 2 fuses in the GREEN box are good.
    Test to see that the 4 diodes in the YELLOW boxes are good.
    Then . . .IF you find no SHORTED diodes . . .proceed . . . . .
    Take DVM and place in DC voltage test mode 50VDC range
    Place test probes across the 2 terminals of one of the units
    LARGE MAIN FILTER CAPS in the BLUE box.
    Turn on unit and leave on just long enough to get a DC reading
    and log down.
    Place test probes across the 2 terminals of the other of the 2 units
    Turn on unit and leave on just long enough to get a DC reading
    and log down.
    Go back to DVM settings and place in AC voltage test mode 50VDC range.
    Follow the same test procedure, but this time you will be logging down
    the amount of ripple across each of those filter capacitors.
    A high ripple content would signify a decline in the capacitance of those
    units over an extended period of time.
    That ripple would show up superimposed on your audio from the speakers
    as a loud HUMMMMMMMMMM . . . . which will even override any control
    by adjustment of the volume control.
    I believe those debased units will be your amps problem.

    If so, they just need replacing to get the unit back to its state of normalcy
    for another 30 years..

    Ask me for a final tip at the very end of the restoration.

    BOARD TOP REFERENCING:

    [​IMG]

    73's de Edd
     
    Last edited by a moderator: Sep 3, 2016
  3. rtripboy

    rtripboy

    2
    0
    Sep 3, 2016
    Thanks so much for the info.Will try this and report back. To be honest I didn't even notice the 2 fuses in the green box. I only replaced the one in the red box.
     
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