Phase Linear Model 1000 Autocorrelator Recap/Update

[AZG]

So this is actually the first recap that I've ever done. I decided to buy a decent solder station give it a shot.

When I opened her up, it looked like someone had already been in there poking around at one point. Maybe you guys can shed some light on some of this stuff...

1. huge bypass cap (1000uf 50v) across the Z4 IC (I removed it but did not replace yet - see photo) why would this be necessary?
2. 4 broken foil traces (3 have been bypassed with wire - see photo) it almost looks like it was done intentionally with a grinding wheel or something. the 4th cut/break was not bypassed so I'm wondering what's up with that?
3. burning/discoloration on a few of the caps (see photo) - is this normal?

I replaced all of the electrolytics with Elna Simic II with exception of a few that Mouser didn't have in stock. I've powered her up and plugged her back in and everything seems to be functioning exactly the same as before. I still think that something isn't right because the dynamic expansion knob has ZERO effect on the sound (which is how it was before the recap).

Any thoughts guys?

 

[laatsch55]

Ya got a service manual?

 

[laatsch55]

If you need boards or parts I think I have 6 of those things left . Don't have but 50 bucks a piece in em...

 

[AZG]

If you need boards or parts I think I have 6 of those things left . Don't have but 50 bucks a piece in em...

Hey Lee,
I downloaded the service manual, but I'm not sure about where to even start with this as far as the foil traces. Especially if it was done on purpose...

Any idea why the IC would be bypassed like that though?

 

[Lazarus Short]

1. I think you're going to like the Elna Silmic II's - it's what I recapped my Cyrus amp with, and it sounds wonderful.

2. Does the wire bridging of the foil traces line up with the traces? A to B, and so on...? Anybody who'd solder a cap across an IC might get creative on circuit connections too.

3. You just never know about some people - my Sumo Charlie would not tune, and I did a careful, close eyeball check of the main board, finally finding a cap at a spot designated for a diode. Sure enough, under the cap was the diode - I removed the cap, replaced the diode, and it tunes like a champ. I'll never know what whoever was trying to do, just as you probably won't with your PL.

4. I just hope you can correct whoever's "hecksperiment."

 

[laatsch55]

Hey Lee,
I downloaded the service manual, but I'm not sure about where to even start with this as far as the foil traces. Especially if it was done on purpose...

Any idea why the IC would be bypassed like that though?

None at all Bud. Have no idea why they would use that value....

 

[AZG]

None at all Bud. Have no idea why they would use that value....

My thoughts exactly. I know that people will bypass with a small 0.1uf cap, but 1000uf??

And to answer Lazarus, the wire bridging does NOT go from A-B...it goes from like A-X (where X is just some other resistor or diode on the board). It really looks like it was done intentionally to re-route the circuit.

 

[NavLinear]

Attached is an abstract of bypass / decoupling capacitors. I found the intro and Capacitance to Filter Corresponding Noise Frequency table on page 4 interesting.

 

[AZG]

Attached is an abstract of bypass / decoupling capacitors. I found the intro and Capacitance to Filter Corresponding Noise Frequency table on page 4 interesting.

Thanks, Nav!