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Post subject: Opto Isolator or Trem Bug
Posted: Mon Mar 16, 2015 9:39 am
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Joined: Wed Feb 18, 2015 10:08 am
Posts: 22
Location: Falun, Sweden
Ok so I had two issues with the vibrato on my '68 Bandmaster.

These were ticking and it was missing a beat here and there which was rather irritating.

I tried just about everything under the 'tick' cure heading and it persisted.

Finally I replaced the trem 'bug' with the genuine Fender part.

The tick has pretty much disappeared. It's more like a really quiet heartbeat now, you can just about hear it if you're listening for it but it is not at all intrusive. Probably the way the amp left the factory.

The missing beat, that I previously described as 'morsecode-like' is cured. Nice constant vibrato.

The really interesting thing was cutting open the old bug. I shall try and post a couple of photos.

The neon bulb had some discolouration/soot marking internally. Perhaps a slight loss of vacuum over the years allowing that. The sensor just looked like it had suffered old age.

Anyhow, if you have a similar issue for the sake of $9 this cured it for me. :mrgreen:
Thought I'd share............


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Post subject: Re: Opto Isolator or Trem Bug
Posted: Mon Mar 16, 2015 9:53 am
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Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
Value drift in a vintage amp's aging components is a double-edged sword, with the results sometimes audibly pleasing -- other times, less so. The opto-isolator in a trem circuit is no exception.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Opto Isolator or Trem Bug
Posted: Mon Mar 16, 2015 9:40 pm
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Professional Musician
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Joined: Thu Aug 07, 2014 3:25 pm
Posts: 1023
Since you have already disassembled the old one, look closely at the sensor leads where they connect to the silvery surface. The connection there is sensitive to vibration and breaks contact there. Twist the lead and see if it rotates there.
That connection can be repaired. First, epoxy the lead where it goes through the backside of the sensor for better mechanical stability. Then use a dab of silver loaded trace repair glue on the frontside to rebuild the connection.
The glue is more expensive than the part, but if you have it on hand, it's a quicker turnaround than waiting for the part to ship in.
Then use new heatshrink and silicone the sensor end where the leads come out.


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