Recapping process

[xoaphexox]

I sat down today and compared some of the capacitors in the service manual with the ones physcially on the board. So far everything checks out.

I am about to order the parts but want to make sure what I am starting out doing is good enough.

This is a QRX-7001.

Someone please correct me if I am wrong or if what I am doing is either unneccessary or not enough!

I plan on doing the recap of this unit in steps. Currently the unit is functioning fine, but has all stock parts so I would like to prolong its life.

Here are the boards I have chosen to begin my recap with:

Driver board (front and back) (F-2436)
Power board (F-2427)
Protection board (F-1461)
Equalizer board (F-2428)
Main power supply caps (2x 10000uf 50V and 1x 1000uf 63V)

All in all its 35 capacitors. Previously I have recapped the crossovers in three pairs of SP-3500 speakers, so I am comfortable enough with the process.

Am I focusing my efforts on the proper areas of the receiver? In honesty the FM tuner portion of this unit is of no use to me, as I use phono/aux inputs exclusively. I also don't use QS/SQ or CD-4 very much (I know its a sin), so I am leaving those boards alone for now.

Power and signal path is what I have read is key. I want to be sure I am hitting the right areas.

Thanks everyone.

Update: I ran to digi-key and every part I needed was right there. I am unsure about the big caps though... are they considered "snap in"? Here is the cart I threw together:

P10323-ND CAP 100UF 50V ELECT FC RADIAL
P10195-ND CAP 100UF 6.3V ELECT FC RADIAL
P10221-ND CAP 470UF 10V ELECT FC RADIAL
P10312-ND CAP 1UF 50V ELECT FC RADIAL
P10320-ND CAP 33UF 50V ELECT FC RADIAL
P12704-ND CAP 470UF 6.3V ELECT FC RADIAL
P1196-ND CAP ELECT 1.0UF 50V SU BI-POLAR
P1142-ND CAP ELECT 47UF 6.3V SU BI-POLAR
P10313-ND CAP 2.2UF 50V ELECT FC RADIAL
P11196-ND CAP 47UF 16V ELECT FC RADIAL
P6690-ND CAPACITOR 10000UF 50V ELECT TSHA
P7470-ND CAPACITOR 1000UF 63V ELECT TSHA

Those last two are the big ones, and most expensive, so I would hate to order the wrong thing. From the picture it looks like something I could use though.

 

[QuadBob]

Hey Rob,

I would say that you're just really getting a good start. You've identified 35 caps you plan to replace. The QRX-7001 has either 199 or 207 electrolytic caps in it (depending on production variations). So, you're planning on leaving approx. 4/5 of the of the 30 year old caps in there.

Will that make an improvement........yes. Enough to be audible.....maybe (OK probably), but it really is neither logical nor really dealing with the issue.

Here's some experienced guidance.....

#1 You have to think of the 7001 as a "system", each area or pcb isn't an individual....it both depends and affects all the pcbs in the system!

Example: You identified the pcb number for F-2428 which is the the Filter and power supply pcb (you called it the EQ pcb....which is F-2458). It provides the low and high filters for any audio passing through the 7001. And, even if you don't "select" the filters....they still have an affect as ALL audio signals pass through this circuit (so they can be filtered or not).

It also provides the "sub" power supply generating 25vdc which supplies the 2087/2088 decoder pcbs and F-2090 demodulator pcb. The same power supply also generates 38vdc which is the main "pre-amp" power supply.

Now from your post, I'm not sure if you meant to recap F-2428 Filter and power supply PCB or the F-2458 the Phono/EQ pcb. but let me guess that you meant the Phono pcb. Then you are leaving the power supply for the Phono pcb AND the entire preamp section unrestored. Will that affect sound and performance.....absolutely! ALL AUDIO signals go through the preamp section....if you don't restore it, you'll simply be feeding garbage into your freshly restored amp section!

#2 Even if you add F-2428 to your list and restore it, and leave just 2087/2088/2090 untouched because you don't plan to use the demodulator or decoder capability (a shame.........). You should understand that the same power supply that feeds 25vdc to those pcbs also supplies the 39vdc to the Tone Control PCB, F-2425 which besides being the "tone" control for the QRX-7001 also serves as the four channel pre-amp section. So, at a minimum you need to include F-2428 and F-2425 simply to deal with the straight four-channel "signal path".......along with F-2423 Filter and Switch PCB as again the audio signal flows through this path ALWAYS.

#3 Ok, so you do all those pcbs and just skip F2087/2088/2090. You need to understand that "weak" old caps in those boards will cause excessive current draw and can generate noise back into its power supply on F-2428 which just happens to also provide the power supply for the preamp and phono EQ! Can it have an "audible" effect.......definitely!

#4 Ok.....what if you "pull" or disconnect F2087/2088/2090? No induced problems then! However, you'll find that you cannot properly calibrate or control the 25vdc/39vdc power supply! As it only has one adjustment pot....and the circuit is designed to be calibrated "under load".....eliminate the load and your 25vdc voltage will jump right up to about 39vdc and you won't be able to "turn it down" enough! Then you won't be able to properly "set" the 39 vdc for the preamp supply, audible result.....either too much or not enough "gain" in the preamp section.

About the only "safe" place you can skip is the F-1507 tuner section, simply because it has its "own" power supply F-2431 (which is built onto the end of the tuner module)........but OOPS, F-2431 which generates 12vdc for the tuner section....draws its power from guess where? Yep, the 39vdc which also drives the preamp section. Bad caps/excessive current in the tuner section.....sucks the power supply for the preamp!

Get it?

Well at least once you get those 35 done.......you'll only have 164 left to do!@: Good luck :banana: ,

QB

 

[xoaphexox]

Awesome QuadBob, thanks for totally "schooling" me. That reply is just what I needed. I really understood what you are getting at. Tonight I will sit down and make the list for the rest of the caps.... I guess my last question would be about those three power supply caps then (the last two on the list I posted). Will the "snap-in" ones work? The photos on Digi-Key looked very close. I opened up the image of the restored QRX-777 you sent me and the caps you had in there look like they are held in place with some foam since they are smaller - excellent idea.

Lastly, the last post I left was really for a QRX-777. The gentlemen at stereomanuals.com sold me a QRX-7001 service manual and said they are exactly the same - is this so? I must have read the EQ's PCB # wrong then, unless there are 777/7001 numbering differences.

Thank you very much for taking the time to help a beginner like myself out - you are truely a class act!

 

[krkier]

P10323-ND CAP 100UF 50V ELECT FC RADIAL
P10195-ND CAP 100UF 6.3V ELECT FC RADIAL
P10221-ND CAP 470UF 10V ELECT FC RADIAL
P10312-ND CAP 1UF 50V ELECT FC RADIAL
P10320-ND CAP 33UF 50V ELECT FC RADIAL
P12704-ND CAP 470UF 6.3V ELECT FC RADIAL
P1196-ND CAP ELECT 1.0UF 50V SU BI-POLAR
P1142-ND CAP ELECT 47UF 6.3V SU BI-POLAR
P10313-ND CAP 2.2UF 50V ELECT FC RADIAL
P11196-ND CAP 47UF 16V ELECT FC RADIAL
P6690-ND CAPACITOR 10000UF 50V ELECT TSHA
P7470-ND CAPACITOR 1000UF 63V ELECT TSHA

Those are all Panasonics:

Series FC
Series SU
Series TSHA

Snap-In is the way the leads were formed, so after insertion of the capacitor into the printed cirquit board it won't shake nor fall off during wave soldering process.

Excellent choice, btw. Those Panasonics are beautiful capacitors for restoring.

Here's the Panasonic webpage. Look under Passive and Electromechanical.

-Kristian

 

[xoaphexox]

Thanks, Kristian.

It looks like those power supply caps I picked out will work then. If only there wasn't a lead time until September 9th! Is there a reccomended place other than Digi-Key for these type of parts? I get my polypropylene crossover caps from partsexpress, but I see neither Panasonic nor 10000uf caps there. In electronics class, we used to get all our parts from Mouser, but that was 8 years ago.

 

[xoaphexox]

Those with any interest in this thread might want to follow it over at AudioKarma, where it seems to be getting more attention:

http://audiokarma.org/forums/forumdisplay.php?f=39

 

[Dylan Berichon]

Thanks, Kristian.

It looks like those power supply caps I picked out will work then. If only there wasn't a lead time until September 9th! Is there a reccomended place other than Digi-Key for these type of parts? I get my polypropylene crossover caps from partsexpress, but I see neither Panasonic nor 10000uf caps there. In electronics class, we used to get all our parts from Mouser, but that was 8 years ago.

Mouser is still around, but Digi-Key is probably your best bet.