Fender optocoupler

[Randall]

Anyone know offhand what the resistive side should be in a Fender style optocoupler when disconnected from the board? I have one that is slowly rising in value while on the meter.

Issue is '66 Pro Reverb AA165 with light side of opto flashing when switched on, but no Tremolo. And, with it switched off, the intensity pot lowers the channel 2 volume as it is turned up, as though the opto was stuck in conduct mode and partially grounding the signal. It was ticking, so I hit some solder joints, and now I have this, so I'm thinking it damaged the opto.

Can I get an Amen on this?

[Leo_Gnardo]

Last I measured one it was well into the megs, say 4 M ohm & no change of R. In Fenders & Boogies I've seen 'em very rarely go bad. But they can. I've had to change out fewer than a dozen over the course of decades. I'd say you got a baddie.

FWIW I've seen a do it yourself suggestion on this kind of opto. Stuff an LED, say superbright orange in one end of a piece of black heatshrink. Photocell in the other, slide 'em right up against each other & heat the shrink. Photocell can be the one intended for Morley replacement, I get 'em from Antique/Tubes&More/CE. Got a project coming up that needs photocells, I'm gonna try making my own this way.

[Jazz P Bass]

Dark, the resistance should be about 1 meg.

[Randall]

Thanks guys. Mine started out at about 1K and has risen to about 32K in about 30 minutes, so I'd say it time to replace it.

[AmpFix]

With the part number, you can get the datasheet for it and get the proper values. There are a few factors to consider in terms of measured resistance.

[Jazz P Bass]

There is a datasheet available for a Fender roach??????

[J M Fahey]

Mine started out at about 1K and has risen to about 32K in about 30 minutes,

That counts as a shorted one, it should reach 100k in less than a second and near 1 M in a minute or so.
Remember that the classic Fender circuit demands a Neon lamp, not a Led, even if orange.
Now all modern Optos are Led based and meant to light with 5V or less.
I make mine (never ever bought one) for peanuts: 5mm CDS cells, bought by the 200 bag (meant for automatic brightness control in TVs) and high efficiency Red Leds, which work way better than equivalent Greens (long story).
I clip the rounded plastic Led tip for a better flat to flat contact with CDS cell, since both are 5mm diameter, 1/4" heat shrink is perfect.