P.A. poawered cab problem

[Rick Willits]

I have two late 70's Yamaha powered p.a. cabinets. I have been using them as monitors for practice and rehearsals. SA 4115's sound great have been working great.
Recently I get no audio from one cabinet. I pull and insert the input cale 4 or 5 times and signal is restored. Works great . Shut down. Next day same routine.
Have used different cables. Have deoxed all connectors. What might be the problem? The input jacks are cpb mounted. Same routine on both of the input jacks so leads me to believe its not the input jack or cable.

 

[WRM]

It sounds to me like the contact on the input jack has lost its' "spring" and is not making a good contact with the cable plug. Like me, it's old and tired?...

Just a thought, good luck!

 

[Rick Willits]

It sounds to me like the contact on the input jack has lost its' "spring" and is not making a good contact with the cable plug. Like me, it's old and tired?...

Just a thought, good luck!

 

[Rick Willits]

Should have mentioned that i adjusted the input jack tension. Thanks for respinse

 

[Old Garage-Bander]

It's possible that you have a bad solder joint where one of the jacks attaches at the PCB.
PCB's can develop cracks in the traces as well.
Are these 1/4" or Speakon?
A lot of knockoff Speakons (ones that are not Neutrik brand) have presented with problems for a lot of folks.
If any of your connectors on the cabs or your cables are not Neutrik, you should have them changed.

 

[Redbrangus]

I'm pretty sure this late '70s cab predates Speak-ons. But you're right about how it might be a cracked solder joint at the PCB.

 

[WRM]

I'm pretty sure this late '70s cab predates Speak-ons. But you're right about how it might be a cracked solder joint at the PCB.

Yep, if it's not the cable/source, and Amp is fine otherwise, logic dicates that it must be the input socket or connection to the amp circuit, and that doesn't leave much.

 

[crazyBassClown]

What might be the problem?

Taking your assertion that it isn't the input jack or cable as true, a bad connection or cracked solder joint or short at any point from there through the amp and even in the speaker driver potentially.
A intermittently bad component in the amp. A bad connection in the power supply somewhere possibly.
Without actually testing the amp it is impossible to know.

If you could diagnose what was wrong with electronics from a 30 second description repairs would be a whole lot cheaper than they are.

 

[Lostgallifreyan]

It's possible that you have a bad solder joint where one of the jacks attaches at the PCB.
PCB's can develop cracks in the traces as well.
Are these 1/4" or Speakon?
A lot of knockoff Speakons (ones that are not Neutrik brand) have presented with problems for a lot of folks.
If any of your connectors on the cabs or your cables are not Neutrik, you should have them changed.

Just backing up this, because it covers all the likely bases while adding nothing unneeded. The 70's were a while ago! Boards were usually made of paxolin (resin bonded paper), not fibreglass, so they can be very fragile. Any connector directly attached to one means you need to examine the whole area around them. Repair with generous soldering is probably easier than detailed examination, so it's worth trying.

EDIT: Check continuity in switches too. Especially rocker switches if any. Those can cause failure like unexpected shutdowns because as they fail, the mechanics might weaken but still get an initial contact that lasts long enough for the eventual failure during a session to appear to have other causes, as oxidation and arcing cause disconnection in the switch once you start drawing more power through it.

 

[Slevage]

It's possible that you have a bad solder joint where one of the jacks attaches at the PCB.
PCB's can develop cracks in the traces as well.
Are these 1/4" or Speakon?
A lot of knockoff Speakons (ones that are not Neutrik brand) have presented with problems for a lot of folks.
If any of your connectors on the cabs or your cables are not Neutrik, you should have them changed.

Speakons? They are powered cabinets.

 

[Redbrangus]

Now that I remember what this cab is, the OP is to be commended for having a pair still in service. Or rather, Yamaha is. This vintage of Yamaha audio stuff may not have been the most elegant designs, but they were about as durable as anything ever produced.

Note that the full-range input signal will also pass through the bi-amp input jacks and switching circuits and they may need the same attention given to the full-range jacks. If/when the symptom reoccurs, leave the full-range connection as it is and try inserting and removing a plug into the LF bi-amp input jack to see if that affects it.

 

[genesound]

If the input jack has switch contact points, they may be corroded. Try some DeoxIT on the points. Doesn't take much at all.

 

[Rick Willits]

I deoxed all the molex connectors inside the cabinet and seema to have corrected the issue so far. Thanks for all the useful comments. Saved a lot of headaches annd more significantly , money. There is a reason i am using 45 year old equipment.