Pearl 3 No Gain

[Toys4Boys]

I managed to fry(?) something in my P3, while swapping it in and out to compare with a Parasound JC Jr. I mistakenly reversed the ins and outs, would this be the likely issue?

 

[6sX7]

pop it open and see if anything looks toasty.

then time to check the active devices.

pictures would be very helpful.

 

[Toys4Boys]

It doesn't have any signs of burning, I'll send some pics shortly. My uneducated guess is the active devices. I am getting some sound, RIAA seems like its ok, just no gain.

 

[Toys4Boys]

A little porn for your viewing pleasure.

 

[6L6]

So what exactly happened?

 

[runclesid]

Look at voltages on the jfet input devices (2SK209). Much of the gain is there and if they are shorted it would lose a lot of it. Since they are directly connected to the input, a good place to start.

 

[Toys4Boys]

Was doing a little compararama with a Parasound and when I switched back to the P# I reversed ins and outs.

Got to head out for a bit, will check voltages when I get back, thx!

 

[Toys4Boys]

@runclesid, a little more specifics of how to and what to look for if you would.

 

[Toys4Boys]

So, the RIAA is fine, it's just way down in gain, maybe 20dB, but now I really have to get going!

 

[runclesid]

On the schematic shared previously, the voltages across the drain to source is one thing to check. The ones in red on this schematic are typical. 6.3Vdc on the drain and 0.08Vdc on the source. If they are shorted, even one of them, the voltages will be the same and a low voltage near 0.08Vdc. If Q5 is bad, then that will change it too. From the top with Q8 to Q5 and then Q1-4 you need voltages comparable to the ones in the schematic.

You lost both channels? If yes, check the +15 supply that it's at the proper level too.

 

[bentconvert]

Fuse?

 

[Toys4Boys]

Notating the test points, thank you @runclesid, the bottom 2 test points, 19v & -19V, are those a source, 19v and drain, -19v? Not importanr for the task at hand, but every little bit helps

 

[freebee]

Perhaps change the dipswitch to MM (and bridge the pins). Afterwards change settings back to your MC cartridge. For some reason this solved a similar issue I had after changing cartridges 🤔.

 

[Toys4Boys]

Hmm, pretty certain I tried playing around with the jumpers, thanks for the suggestion. I've already replaced it in my system and made a chart for test points so...

 

[wayne]

Does the other phono stage still work? There is possible potential to damage the cartridge.

 

[Toys4Boys]

Cartridge is fine

 

[freebee]

In that case he should be able to measure the MC coils to verify, correct?

 

[Toys4Boys]

Uh, hold off on that, I need to try it with the JC Jr. Thanks for the suggestion.

 

[freebee]

If cartridge is playing fine with another phono amp then there is no need to measure the coils.

 

[Toys4Boys]

The cartridge is fine, so I got that going for me.