Bose Series IV equalizer RCA connection issue

[bringarecord]

Hello,

Looking for some input on an issue I haven’t found a thread for. I recently re-foamed some Bose 901 series IV speakers. I’m aware of the polarizing nature and quality of the parts in the equalizer but at the right price I was able to get a relatively clean pair to clean up.

While I was setting them up I accidentally dropped the equalizer. It had worked during testing but when I plugged it in post drop, I couldn’t get any sound through the Tape 2 loop when plugged in correctly. Powers on and when I opened it up I couldn’t see any damage or severed connections.



Yet, when I touch the pins to the outside of the RCA connections, I’m able to get sound to pass through fine.



I’m relatively new to this hobby and learning, but this called for some assistance in understanding what the problem could be and how to potentially fix it.

Appreciate any advice I can get.

 

[wmgwizard]

"when I opened it up I couldn’t see any damage or severed connections."

Look closer....a bright light and magnifying glass will help. Something broke loose somewhere as it is unlikely the physical shock caused a electrical failure beyond possibly breaking a fuse filament.

You could also do a chopstick test.
Plug everything in normally and start poking and pressing gently on components searching for the sound.

 

[Bill Ferris]

By the way, all the RCA in/out connectors are visually shifted over to the right of the chassis holes (non centered) for them, it wouldn`t surprise me if the circuit board`s attachment point`s that their mounted to, have become cracked somewhere from the "uncontrolled decent" and resultant impact, especially, if the unit hit a unforgiving hard surface like ceramic tile or concrete from a table`s height !

I`d carefully examine with very good lighting and even using a magnifier, the bottom/underside of the circuit board`s circuit traces, especially at or near the circuit board`s attachment points to the chassis areas, and any of the front panel circuit board mounted controls/switches for any physical damage that could result in breaking the signal path, or the device`s internal operating voltage`s distribution paths.

Butterfinger event`s results usually don`t go well.

Good luck with tracking down the issue(s)

 

[toddalin]

The jacks are really off center. When you dropped it, perhaps you did this and maybe now the ground is shorting to the case and is not supposed to. Can you tweak the circuit board back into place enough to avoid anything touching the case?

 

[bringarecord]

Thank you all for the guidance. I’ve got a new mag shop light on order to take up your advice. I’ll post my progress in the coming days. I’ll work on realigning the board to center the jacks as well.

 

[f0427ea]

The jacks are really off center. When you dropped it, perhaps you did this and maybe now the ground is shorting to the case and is not supposed to. Can you tweak the circuit board back into place enough to avoid anything touching the case?

^^this^^

 

[bringarecord]

Update on progress:
I took the board out and checked for any obvious breakage or other indications of damage. Nothing obvious. I tested the signal between the RCA connections with a multimeter on the inside of the board to the next point along the traces. All points were clear, no blockage.



I then reconnected the board but left the wood housing off to reconnect and test.

Additionally I did double check the Tape 2 loop on the receiver and RCA cables. Confirmed both were operational.

I plugged in the Equalizer to the Receiver’s Tape 2 loop and for one glorious minute, success when I had engaged the Tape 2 button. Both on and off had signal passing through.


Thinking the problem was resolved I unplugged the cables to reattach the wooden housing and then plugged everything back in. Now nothing again. When I engage the Tape 2 button, no sound. I took the wood housing off again and retested. Nothing again.

I did take a portable music player directly into the EQ input and the output into the AUX on the receiver to see if anything was passing through the EQ at all. Nothing.

When I lightly place the RCA pins into the EQ AMP output I get a buzz in the speakers but once I fully plug them in, no sound at all.

So, I definitely think the problem is with the EQ but could use some advice on next places to check.

Thanks all.