RT-909 Level Problem

[1mike161]

My RT-909 has a problem where the output on the L channel during FWD Play drops by two meter segments on an intermittent basis. The problem is cleared by pausing and un-pausing playback. Reversing play direction (FWD to REV then REV to FWD) also clears the problem. I have confirmed this by playing a 700Hz/0dB calibration tape and measuring the L channel voltage on the output terminal. The voltage drops from 450mV to 380mV when the problem occurs.

My attempt to trace and troubleshoot lead me to observe a corresponding voltage drop on the L FWD Play in the P.B. EQ AMP section at the OpAmp output pin (see diagram). Here the voltage drops from 300mV to 285mV.

Asking as a novice, is the problem with the OpAmp, OpAmp support component, cold solder joint, or something else? Is this a known and/or common occurrence, or is this a sign that a 40 year old deck needs restoration work? Any advise would be appreciated. Thanks.

 

[markthefixer]

I don't know offhand how many mechanical switches are in it, but it sounds like a classic need for deoxiting all the switches that carry audio.

 

[1mike161]

I don't know offhand how many mechanical switches are in it, but it sounds like a classic need for deoxiting all the switches that carry audio.

Thanks! I did think of that and I cleaned all the suspect switches with Deoxit. However, I was concerned that the Deoxit was not working it's way into the switches properly -- I'm not sure if I was spraying into the correct holes.

 

[markthefixer]

you can check a set of contacts with an ohmmeter,
ghosting isn't much of a problem when you are looking for the equivalent of a short circuit at the probes.

it's a lot of work, but I do that with every switch to be sure. I even toggle them to be sure it's repeatable.

after that, well... fingers crossed..

 

[1mike161]

you can check a set of contacts with an ohmmeter,
ghosting isn't much of a problem when you are looking for the equivalent of a short circuit at the probes.

it's a lot of work, but I do that with every switch to be sure. I even toggle them to be sure it's repeatable.

after that, well... fingers crossed..

Good idea. I'll give that a try next. Thanks again!