API 5500 TROUBLE HELP!

[TunnelStudio]

Hi guys. I have a problem on a section "HI" freq of right channel. The rotary switch works at 15k only in shelving mode. In peak mode I only have a gain increase of channel, no frequency boost or cut. All frequencies of the rotary switch work, 15k in peak mode does not work. Do you have any experience like this or ideas?
Thank you

Nico

 

[john12ax7]

Is this a recent occurrence? This seems like something came loose or disconnected inside. Was it shipped recently?

 

[PRR]

The coil may be shorted.

 

[TunnelStudio]

Is this a recent occurrence? This seems like something came loose or disconnected inside. Was it shipped recently?

It's a product of 2011, I bought it used a month ago. the previous owner claims he does not know anything about the defect. I tried to give little hits on the capacitors but nothing happens. I emailed Api and they say sound like a bad rotary switch.

The coil may be shorted.

Hi RRR, why not bad rotary switch?

 

[john12ax7]

It depends on the topology. It's possible the rotary switch is shorting (or not connecting) the components that define the filter. Or the components themselves are bad.

 

[TunnelStudio]

It depends on the topology. It's possible the rotary switch is shorting (or not connecting) the components that define the filter. Or the components themselves are bad.

thanks, this is making me crazy

 

[Tekay]

Sounds like a shorted cap.

 

[TunnelStudio]

Breaking news! At 15k the volume defect is gone. in peak mode it is completely dead. Funny  :'(

 

[ruairioflaherty]

The coil may be shorted.

No coil in an API 5500 unfortunately…  all caps.

Tunnelstudio,

Where are you located?  And how comfortable are you in trouble shooting this yourself?  Do you have an oscilloscope?

The schematic for the 5500 is not available but we know that it is derived from the API 550 topology so there is a lot we can learn from that about where the fault will be.

 

[Chris]

It's very possible that a defective switch is at fault. I had a similar issue with a 550A reissue a while back; missing boost or cut at certain bass frequencies only in shelf mode.  Replacing the entire concentric bass switch fixed the problem.

Chris

 

[TunnelStudio]

No coil in an API 5500 unfortunately…  all caps.

Tunnelstudio,

Where are you located?  And how comfortable are you in trouble shooting this yourself?  Do you have an oscilloscope?

The schematic for the 5500 is not available but we know that it is derived from the API 550 topology so there is a lot we can learn from that about where the fault will be.

I'm in Italy,  personally have no experience in electronics. My friend should operate the toy, he has all the skills. I'm trying to figure out from your experiences what the problem might be.

It's very possible that a defective switch is at fault. I had a similar issue with a 550A reissue a while back; missing boost or cut at certain bass frequencies only in shelf mode.  Replacing the entire concentric bass switch fixed the problem.

Chris

Chris this is good news. We could try to swap the switches.

 

[TunnelStudio]

Thank you all!! I update you after the Christmas holidays!

p.s: if you still have suggestions it will be easier to go to act in a more targeted way.

Nico

 

[fazer]

I have 550s from the late 70’s.  Some have acted like this .  I use electrical cleaner and exercise the switches and gotten all of them to come back .  Also the peak shelf switches have stopped working and again cleaner with exercising the switch brings it back to life.  I’ve never had to replace a switch.  I don’t have experience with the newer SMD versions.

 

[Rob Flinn]

It's very possible that a defective switch is at fault. I had a similar issue with a 550A reissue a while back; missing boost or cut at certain bass frequencies only in shelf mode.  Replacing the entire concentric bass switch fixed the problem.

Chris

I had one on the bench with a bad switch.  I emailed API & they way they talked it came across as if this isn't a very rare occurence. Advised owner to send back to API since it was dual concentric with about 6 wafers.    Figured if they trash the PCB taking the old one out they can't charge for damage they had done.  Whereas if I damaged board I would be liable to client ..