Tone Board modded 488 Amp

[carlski]

Hello, Carl here novice,
I am wondering if anyone has seen this Mod or can just explain why it was done.
Tone Control Board 52260-A           on Amp  52280-A
Q3 & Q6 have had a resister and a Cap added.  seem to be M 2N4392313.   Rockola52342 N - Channel Junction Fe


link

Have seen somewhere that someone replaced tiatanium transister with alternate parts will try and find again(thinking these maybe them and just faulty)
sorry if links dont work can take me a few goes to get working

[Ron Rich]

Hi Carl,

Just guessing here---
If a factory modification, it could have been in response to "field complaints" of failure of this transistor, and/or the engineering staff "justifying their existence" (LOL). Unless one can find a written explanation, like a "factory bulletin", that's the best I can do-- Ron Rich

[jukenorman]

I've had a look at the schematic - the modification will alter the treble response somehow. These components tie in to those that are put in circuit by the treble slider switches. Where the resistor is connected to the transistor leg, that is just a ground point. Sometimes mods like that are done for the strangest of reasons - for example, maybe the upper speakers were changed out for something not totally suitable and that mod compensates?

Norman.

[carlski]

Hi
Thanks for info. Would a loose faulty treble switch be a reason as the right high contact is not great.
Going to just leave as is. Was concerned it may have joineed R&L channel(because only one working and I have an open large speaker and a very loud squeal buzz in small speaker if channel connected)
Again thanks
CarL

ps please ignore line of dribble about transistor in first post(possibly just tied?)
think I was maybe confused with "driver board" as thinking thats where lost channel fault lies.

[Ron Rich]

Hi Carl,

Yes-- if that switch has "loosened" it can cause all sorta-problems-- It switches both channels at the same time. Should be an easy fix-- de-solder it from the board. Once free, turn it over -- look at the crimps-- and use a needle nose to re-tighten the crimps- Clean it with a "safety solvent"-- then use a good contact cleaner on it ( I suggest "Deoxit-5", if you can get it)-- check it with an Analog meter--- Ron Rich

[carlski]

Hello Ron
Could you please clarify about treble switch. Switching both channels at same time. As there are left and right switchs for both
treble and bass. I have to admit I can very easily get lost in a schematic(there is one in the link under second picture)
Cheers Carl

[Ron Rich]

Hi Carl,
Yes-- I can "clarify" this--I'm STUPID, and wrong-- You are correct-- each channel has it's own switch, in this case-sorry, Ron Rich -

[carlski]

Hi Ron
Cheers, dont think many on site would agree with you on that lol
Carl