Recap of SAE P102 Preamp

[budm]

Re: Recap of SAE P102 Preamp

Do you have any lytics 4.7uF 25V cap? You do not have any broken boards?

[clearchris]

Re: Recap of SAE P102 Preamp

I have tons of electroylics, can they be subbed in? I assumed you said film cap for a reason.

[budm]

Re: Recap of SAE P102 Preamp

Film cap has no polarity. 4.7uf (10uf be fine too) 25V will be fine, put the + on the end that is connected to the resistor leg

[clearchris]

Re: Recap of SAE P102 Preamp

Thanks! Soldered up a harness with an rca jack, probe, clamp, resistor and 4.7uf 100v cap. Testing begins tomorrow!

[clearchris]

Re: Recap of SAE P102 Preamp

Progress! Signal on both channels makes it out of IC304. Signal on only one channel seems to arrive at IC306. So, IC305 or something else in the neighborhood is suspect.

Now to put on another pot of coffee and cuddle up with the schematic.

Edit: Not much going on between IC304 and IC306. I really hope the CPU isn't toast.

[clearchris]

Re: Recap of SAE P102 Preamp

All inputs and outputs of IC305 have signal. That narrows things down quite a bit. Right now my suspects are C324L, R322L, C319(L?) and R323L.

[clearchris]

Re: Recap of SAE P102 Preamp

Signal going into R322L none on the opposite side. Pulled the resistor, checked fine. Took a closer look at the board and found a solder bridge. I must have flowed it when I pulled a nearby opamp, because I didn't touch this joint. A bit too much heat on the board apparently or maybe I nicked it with the iron. These are easily the thinnest gaps on the board. Glad I didn't fry anything.

Before fix:


After fix:


Fired it up, sounds great!

Special thanks to redwire and budm!

Now I'm going to put it back into my rack, crank some tunes and upload my notes.

[budm]

Re: Recap of SAE P102 Preamp

Thank you for the feedback, glad you got it working.

[clearchris]

Re: Recap of SAE P102 Preamp

Disassembly is pretty straightforward. To do a recap, I'd strongly suggest to remove the face. Putting the cables back in sucks, but if you have a hollow needle set, they are helpful to straighten the cable ends. They really made me thankful for real ribbon cables, these seem like wires lightly glued to clear plastic. Also, after disassembling it, reattach the sides, and cover the top and bottom of the sides with blue tape. You are going to be flipping this endlessly, attaching the sides lets it sit straight, and doesn't put all the weight on the transformer and heat sinks. Putting blue tape on the sides will keep it from scuffing.

I have the revision 1 of the board, the service manual references revision 2 I believe. There may be some differences and there may be more revisions. So be cautious, my notes may or may not apply to your board.

Before starting, I suggest marking the empty cap spaces. I use a silver sharpie, there are a few empty spots and it's easy to get confused. Also mark all the existing caps you plan on replacing. I use a black sharpie, so it's easy to spot the remaining caps.

Special notes:
C307L/R are backwards on the silkscreen. Pay special attention before you remove them. I suggest marking the board.
Many (most) of the electrolytic caps marked as 100v are actually 10v on the board. 100v caps will not fit in many of the spaces, so you should pick up some lower voltage.
IIRC, some of the caps in the 7xx section are marked lower voltage in the service manual than they are on the board. Verify.
Clean off as much of the black glue in the power section as you can. Acetone will dissolve it. Some of the glue had touched the heat sinks, and there was corrosion there.
Consider going with higher voltage caps in the 7xx section, the whole section looks pretty toasty. There is limited space around C709, C710, C713 and C714, consider getting taller caps if you can. I fit some panasonic 35v or 50v there, but space was super tight.
The service manual lists some very small value electrolytic caps, but they are ceramic. Once the first ceramic cap is listed in the manual, there are no more electrolytic caps.
Many of the mylar cap values are different on my board than in the service manual. Verify before buying and replacing. I have listed the values found on my board in the audio path (not phono section though) on the attached notes.

I replaced IC206, IC301, IC304 and IC306 with a socket and an upgraded opamp.
3m 8 pin socket: 4808-3000-CP don't buy this one though, get the one with bent pins.
opamp: OPA2134PA
IC401, IC403 and IC101 were replaced with the same socket and NJM4558DD. Really wasn't needed for the two opamps that feed the LEDs, but I did it anyway. Per redwire, you don't want to use an OPA2134PA for the phono section.
If you replace the opamps, remove the bottom middle case/board support.

While you are in there, you should probably tune the oscillator for the CPU, and tune the LEDs. I didn't do either because 1) my frequency counter is in the mail, and 2) I wanted to get this back in the rack and I'll be opening it up again to replace the mylar caps.

This is a sheet from the service manual. I crossed out the electrolytic caps I replaced. If it's an electroytic cap and I didn't cross it out, it wasn't present on my board. Sometimes a listed electrolytic was a mylar cap on the board. Sometimes the values were different. I dotted the mylar caps in the audio path and the power section, less the phono section. (Sorry, I haven't owned a record player since the 80s.)

And finally, don't believe my notes if it doesn't make any sense, your board could be different, etc.