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Help with Realistic speaker with built in amp

DickFreed

Aug 6, 2021
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The thing just suddenly stopped working while playing a keyboard through it. I can plug it in and hear some slight static, but no loud hums or anything that is concerning(loud).

First question being, as I’m new at attempting repairs, I was randomly checking the diodes with my DMM in diode mode and noticed that they gave around .590 V forward biased, but every one also gave around 2.5 V reverse biased. These were the 4 that lay right beside each other so guessing they are part of the power supply. I was expecting each to show an open circuit. I tested them in circuit. I guess I’m doing it wrong?

When plugged in, the “ON” led glows, so i guess at least some power is going somewhere.

Once I figure out how to correctly test the aforementioned diodes, could I have a suggestion as what to test next?

https://imgur.com/a/uecJxGc
 

Harald Kapp

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Nov 17, 2011
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Once I figure out how to correctly test the aforementioned diodes,
Testing components in-circuit is notoriously difficult and mostly will require special tools. Remove one leg of each diode from the PCB, then test again. This way other components on the PCB cannot change your measurements.
could I have a suggestion as what to test next?
Not next but first: Check the supply voltages within the amp, check any fuses.
 

DickFreed

Aug 6, 2021
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Testing components in-circuit is notoriously difficult and mostly will require special tools. Remove one leg of each diode from the PCB, then test again. This way other components on the PCB cannot change your measurements.


Not next but first: Check the supply voltages within the amp, check any fuses.

I can’t find a schematic and don’t have enough common knowledge apparently to know exactly where I should be checking for supply voltages. I did check what was coming from the transformer into the board, it was 15 volts. I also checked across each of those diodes on both AC and DC settings. The pic I provided of the results show the numbers 1-4 for each diode. #1 being when looking down at the board from above and the actual diodes being in the top-left corner of board.

I made a guess and used the negative side of the largest electrolytic for reference in checking voltage from each cathode of the diodes. I wrote those results as well.

Idk if I still need to unsolder and check the diodes after these results, but I probably will for the heck of it while waiting for a response.

There seem to be no fuses, at least that I can identify.

https://imgur.com/a/9SGsySm
 

Harald Kapp

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Difficult to judge without a schematic but the numbers do look normal.
I'm sorry I don't know how to proceed without a schematic. Usually one would poke around to check where the audio is present and where not to limit the search to an area where the sound "disappears", That will require an oscilloscope or a signal tracer and some patience.
 

DickFreed

Aug 6, 2021
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Difficult to judge without a schematic but the numbers do look normal.
I'm sorry I don't know how to proceed without a schematic. Usually one would poke around to check where the audio is present and where not to limit the search to an area where the sound "disappears", That will require an oscilloscope or a signal tracer and some patience.

I built a cheap signal tracer out of a radio shack book just last night to poke around an elenco radio I built. Making stuff is easy. Fixing stuff, not near as. I’ve got an oscilloscope, I’ll look up how to use one like how you mention. Thanks.
 

DickFreed

Aug 6, 2021
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The numbers I provided in at the beginning of this post are the only identifying things I can find on the whole setup.
 

bertus

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Nov 8, 2019
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Hello,

I do not like to watch external pictures.
Resize them to about 300 kB and post them over here.

Bertus
 
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