Studio Pro 60, Reverb not working

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Telecastoff1
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Studio Pro 60, Reverb not working

Post by Telecastoff1 » Mon May 30, 2022 9:17 pm

I just picked up a Studio Pro 60 this morning. I cleaned all of the pots, jacks and connections with Deoxit. Everything is fine, except for the reverb. It makes a crashing noise when I jar the amplifier, but no reverb output when I'm playing. I pulled the pan and checked for loose or broken wires, they're okay...everything appears normal in the reverb pan. I pulled the reverb molex connector and cleaned those connections. I cleaned the two in/out jacks on the reverb pan. There is a slight "hum" when I turn up the reverb pot. What do you think is the problem? Could it possibly be a bad Op-amp that controls the reverb? If so, which one controls it? I have extras on hand from a special 130 I upgraded a while back that I could use.

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Enzo
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Re: Studio Pro 60, Reverb not working

Post by Enzo » Mon May 30, 2022 11:12 pm

Unplug the pan cables and measure resistance across the jack at each end. The OUTPUT end is working, because you get crash noise. But even though you see no broken wires, the INPUT end coil can still be open.

Unplug again the cable from the INPUT jack, and measure resistance from tip to shell on the RCA plug. Do you get maybe 22k or thereabouts? The number might be different, but what I don't want to see is OPEN.

And sure it is entirely possible the IC is bad, likely a 4558. Where on the board? beats me, I don't have the schematic for that model. I have the 50 but won't assume they are the same layout. You got schematic? Post it.

Telecastoff1
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Re: Studio Pro 60, Reverb not working

Post by Telecastoff1 » Tue May 31, 2022 10:52 pm

It shows resistance on both Input and Output jacks. I'll look further and see if I can find which op-amp controls the reverb on this. I really don't need to have the reverb but, but its going to bug me to no end if I DON'T GET IT WORKING. Thanks for your assistance.

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Enzo
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Re: Studio Pro 60, Reverb not working

Post by Enzo » Tue May 31, 2022 11:52 pm

Do you have the schematic?

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Pappy B
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Re: Studio Pro 60, Reverb not working

Post by Pappy B » Wed Jun 01, 2022 10:32 am

The IC for the reverb is usually the one closest to the molex connector.
The more I learn the more I realize how much I don't know.

Telecastoff1
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Re: Studio Pro 60, Reverb not working

Post by Telecastoff1 » Thu Jun 02, 2022 10:46 pm

Thank you. I'll check it out. I did pull the reverb pan from the amp and installed a a good working MOD pan I had from my SP 50. Same issue, so it's definitely not the pan at fault here. I'll locate the IC, change it out and see if that changes thing for the better.

Telecastoff1
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Re: Studio Pro 60, Reverb not working

Post by Telecastoff1 » Sat Jun 04, 2022 11:14 am

I just replaced the IC, and there was no change. Still no reverb. Actually, it doesn't really matter to me as I have reverb and delay pedals I can use instead. However, the only drawback would be that the resale value would probably me much less without a working onboard reverb.,,,and it's not like the resale value would be that much anyway. It's a bridge I'll cross if or when I get to that point. Thanks so much for your thoughts and assistance with this. It's much appreciated.

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dak
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Re: Studio Pro 60, Reverb not working

Post by dak » Sat Jun 04, 2022 1:19 pm

I like the reverb pan in my KB300. Very organic sound. Probably not easy to emulate well with a pedal.

rogue777
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Re: Studio Pro 60, Reverb not working

Post by rogue777 » Mon Jun 06, 2022 8:42 pm

In Enzo’s first post to your issue. He mentioned three resistance measurements, your response was that you verified the reverb tank input and output coils, two measurements.
The third, being to verify R33 back thru the input cable and the molex connector, as Enzo mentioned is 22k. There was another recent post of someone had a bad molex connection.

https://www.audioservicemanuals.com/p/p ... -schematic

Telecastoff1
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Re: Studio Pro 60, Reverb not working

Post by Telecastoff1 » Mon Jun 20, 2022 9:12 am

I took those measurements and it's all normal and within spec. Molex connector is clean and wire connections to and from Molex connector show continuity, so no broken or intermittent wired connections present there. This one is a mystery. But, I'm not going to spend a lot of time on it. The rest of the amp works just fine and I do have Delay and reverb pedals I can use. I just want the onboard reverb to work in the case I should sell the amp. I refuse to sell an amp that has issues.

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dak
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Re: Studio Pro 60, Reverb not working

Post by dak » Mon Jun 20, 2022 12:13 pm

Well, one test worth doing would be putting reverb volume to full and master to loud enough and then knocking the case. If you hear nothing, the receiving side of the reverb has a problem. If you hear spring noise and rumble, it will be the sending one. You talk of "crashing noise" when hitting the amp; I am not sure whether this is what I am talking about or rather the noise a flaky connection makes.

I've even had an amp where I considered the reverb non-impressive when the sending side was actually defective and I mistook the mechanic pickup of the spring tank from the loudspeaker enough of a reverb to consider it operative.

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