harman/kardon hk725 preamp rebuild

[jheu02]

One other thought about the learning process, frustrating as it is is this: I got to relearn something I hadn't considered recently. For the most part, the orange sleeved caps do equate to low-leakage. However, as was the case here, ELNA used the orange sleeve to designate another special characteristic...BP. This was often done so that service techs would readily see that there's something "non-standard" about that particular part and be sure to use the correct replacement, checking the scat and or service manual.

Here's a link to the Pioneer Tuning Fork series posted over in the Pioneer forum. Post #11 has the Capacitor information. Lots of great info as to what types are used where typically, etc. great reads these tuning forks.

http://audiokarma.org/forums/index.php?threads/pioneer-tuning-fork-service-guide.249745/

 

[z-adamson]

I got it figured out. I took every cap that I removed, which involved me digging through the trash (should not have thrown them away), and I matched them up to the caps I installed by the voltage and uf ratings and it became obvious where the BP caps were by process of elimination.

C207 - 10v, 47uf
C208 - 10v, 47uf
C211 - 16v, 47uf
C212 - 16v, 47uf
C405 - 16v, 47uf
C406 - 16v, 47uf
C503 - 25v, 10uf
C504 - 25v, 10uf

These are all the BP caps and their locations.

 

[z-adamson]

Another thing....diodes.

How is it determined which way to install them? I have a couple zenor diodes to install/remove.

 

[z-adamson]

I could use some pointers in regards to how exactly to bypass the relay in this preamp. I would definitely like to do. Looks like it has 8 soldered joints to the board. I am not 100% as to which solder pads would need to be jumped together.

 

[z-adamson]

One other thought about the learning process, frustrating as it is is this: I got to relearn something I hadn't considered recently. For the most part, the orange sleeved caps do equate to low-leakage. However, as was the case here, ELNA used the orange sleeve to designate another special characteristic...BP. This was often done so that service techs would readily see that there's something "non-standard" about that particular part and be sure to use the correct replacement, checking the scat and or service manual.

Here's a link to the Pioneer Tuning Fork series posted over in the Pioneer forum. Post #11 has the Capacitor information. Lots of great info as to what types are used where typically, etc. great reads these tuning forks.

http://audiokarma.org/forums/index.php?threads/pioneer-tuning-fork-service-guide.249745/

I checked it out. Thanks for the link!

 

[z-adamson]

CE is from the French....Capacitor Electrolytique....and yes, BP is Bipolar. It's a shame that the SM didn't list these (most do) and yes, it could have been a factory enhancement, which is why it wasn't marked. Many feel that using a bipolar cap in coupling situations is better for audio purposes. I don't know if HK had a lower model number in the series which may have used polarized caps and a common board. There's a chance that nothing wrong will happen since you followed the rest of the board layout, but then again... As you said, live and learn.

These would be good caps for C405, 406, 211, 212

http://www.mouser.com/ProductDetail/Nichicon/UES1E470MPM/?qs=sGAEpiMZZMtZ1n0r9vR22e0BBN1kF1oiaRKDk3aXVQU=

As to "reverse engineering" to figure out which went where, you should be able to take the cap value and look at the schematic to give you likely places they were pulled from. Don't worry, we'll get it all sorted out.

Those caps look like 85c rated. Do you think 105c would be preferable?

 

[z-adamson]

This is the relay right? I took a pic of the 4 solder pads from the relay, not sure which to jump to which, and what to use as jumper wire.

 

[z-adamson]

This is what I came up with for a relay bypass system....I think I got it right.

 

[jheu02]

A bit too tired right now to look at it all. The ES Bi polars are what I use if I can get them due to quality. Muse series from Nichicon and you're using many of them in coupling applications. I believe that overrules the temp rating in this case but you may feel differently. Diodes have a band on one end. Has to go in the same way as the original.

 

[jheu02]

Looking back at your list, it surprises me that you found C503 and 504 to be bipolar. They are just referencing ground. It would make more sense to me that C501,502 (4.7uF/25V) and C507,508 (100uF/16V) would be bipolar, or low leakage. C501,502 are input coupling caps to the headphone amp (IC501) and C507,508 are the output coupling caps. Personally, I would only look at bypassing the relay if it was faulty and no replacement could be found.

 

[RWood]

Yes, that is the relay. You could bypass it temporarily if you want, to see if it is causing any of the problems.

If you do decide to bypass it, here is what to do:
Locate the white jacketed wire (containing a red and white hot wire and a ground) on the Input/output Jack PCB (which also contains the relay).
It comes from the Hi Cut board (at R713 and R714).
Desolder this white wire from the In/Out PCB. This is your output signal from the amp.
Resolder this wires to the output jacks, our to any convenient spot near the jacks on the "other side" of the relay.
You don't need to remove the relay to do this, but it looks like you may have already done that.

 

[z-adamson]

Yes, that is the relay. You could bypass it temporarily if you want, to see if it is causing any of the problems.

If you do decide to bypass it, here is what to do:
Locate the white jacketed wire (containing a red and white hot wire and a ground) on the Input/output Jack PCB (which also contains the relay).
It comes from the Hi Cut board (at R713 and R714).
Desolder this white wire from the In/Out PCB. This is your output signal from the amp.
Resolder this wires to the output jacks, our to any convenient spot near the jacks on the "other side" of the relay.
You don't need to remove the relay to do this, but it looks like you may have already done that.

View attachment 930441

Look at post number 68.

Is what you describe any different than what I already did? I basically ran jumpers to jump the solder pads that the relay uses....in other words it is as though the relay is closed all the time. That is what bypassing a relay is all about right?

 

[RWood]

Yep

 

[z-adamson]

Yep

Double checking...

Yep, as in what I did does not accomplish the same thing as what you suggested or Yep, as in what I did does effectively bypass the relay?

 

[RWood]

What you did looks right. I didn't see that post 68 when I wrote mine. I started writing when I saw you ask how to do it. But it looks like you successfully jumped the audio signal over where the relay had been.

Does the amp work?

 

[z-adamson]

What you did looks right. I didn't see that post 68 when I wrote mine. I started writing when I saw you ask how to do it. But it looks like you successfully jumped the audio signal over where the relay had been.

Does the amp work?

I am still in the assembly phase and waiting on bipolar caps to get here from mouser. Thanks for confirmation that I successfully jumped the relay and double thanks for the idea to do so. I turn amps on last and off first anyways, so dont really need the relay.

 

[jheu02]

I turn amps on last and off first anyways, so dont really need the relay.

Yes, but will anybody else be using the stereo? Do you plan to keep it or eventually sell it and try something else?

 

[z-adamson]

Yes, but will anybody else be using the stereo? Do you plan to keep it or eventually sell it and try something else?

Nobody else will be touching any of my audio gear. I will be sure of that. No plans to sell anything audio realed off in the foreseeable future, and if I were to sell I would start with the receivers that have high value in the open market and not the seperates that don't comment much cash.

 

[jheu02]

No worries. If in the future you do decide to pass it on, you may consider either reinstalling the original or replacement relay, or make sure the new owner is aware that the relay has been bypassed. Not all out there treat stereos the same way nor realize that there might be preferred ways of powering up/down systems. Did you ever determine whether the relay actually was the problem?

 

[z-adamson]

No worries. If in the future you do decide to pass it on, you may consider either reinstalling the original or replacement relay, or make sure the new owner is aware that the relay has been bypassed. Not all out there treat stereos the same way nor realize that there might be preferred ways of powering up/down systems. Did you ever determine whether the relay actually was the problem?

That I will do. Bypassing the relay was not an attempt to fix a problem, I was simply trying to eliminate potential problems down the road while this thing is apart and considering that I really don't need the relay, I am better off without it than with it. One less set of contacts for the signal to go through sounds good to me.