Recapping and repairing a Harman Kardon 730 twin power series stereo receiver

[dlucy]

How much of a pain is it to separate boards that are connected together? Do you just pry them apart?

That part is easy, prying the boards apart.

For the tuning needle light that you updated to an LED, where is the yellow wire going to from your homemade board?

The original red wires that powered the original dial pointer lamp went back to posts on the back of the long fuse style lamp board. Those original wires were not long enough to supply my new regulator board, so I replaced them with two yellow wires.

The new yellow wires go to the same spots as the original red wires.

Did you replace the tuning strength light? That particular light does not work on my 730.

No, I did not need to.

 

[Skywatcher]

The open frame trimpots from the 330A, 330B and 330C scare me every time as i've gone to adjust them before, with power on, only to have them physically fall apart.

So, all these units get new sealed trimpots

The three-legged potentiometers need to be turned into two-legged variable resistors, so the middle leg gets bent and shorted to one of the outside legs and soldered together.

View attachment 1646042
View attachment 1646043
View attachment 1646044

And now the trimpots can be safely trimmed with power on

View attachment 1646045

On the 730 I did, that was not necessary. There were already all 3 holes for 3 legged trim pots. 2 holes on the same trace. Yours have them too.

 

[FinalVinyl]

Wow thats a lot of work. Great pictures!

 

[eizner23]

Nice work on the recap as always and I like that pcb repair, looks very solid. Imagine that unit sounds like gold.

 

[dlucy]

Hmmm... this is a new one for me: the 2SC1400 diff amp small signal transistors on the power amp boards have “gone noisy” in the second hk730 I’m working on. They are producing very loud crackling that begins at startup, occurs randomly, not tied to control knob adjustment, not specific to any function selection, and unaffected by volume control.

replacing them with hfe-matched KSC1845F eliminated the crackling, so these 2SC1400 were noisy.

 

[Skywatcher]

Hmmm... this is a new one for me: the 2SC1400 diff amp small signal transistors on the power amp boards have “gone noisy” in the second hk730 I’m working on. They are producing very loud crackling that begins at startup, occurs randomly, not tied to control knob adjustment, not specific to any function selection, and unaffected by volume control.

replacing them with hfe-matched KSC1845F eliminated the crackling, so these 2SC1400 were noisy.

That just goes to prove that you can't trust old silicon. The leads look so shiny and clean too so you can't blame the "black creep" this time.

 

[dlucy]

On the 730 I did, that was not necessary. There were already all 3 holes for 3 legged trim pots. 2 holes on the same trace. Yours have them too.

Right you are! Thanks!

 

[dlucy]

That just goes to prove that you can't trust old silicon. The leads look so shiny and clean too so you can't blame the "black creep" this time.

Yep. Shotgun time!

 

[NAD80]

Doug read the entire thread, Great Job so far.

 

[dlucy]

Ok, looks like this is a great opportunity to restore (i.e. nuke from orbit) the power amp, tone and phono boards....

power amp board first

 

[dlucy]

I have barely had a chance to listen to it, but I am so glad that Doug was able and willing to do the work on this old HK. I plan on listening to it for many years to come.

how does the hk 730 twin power sound now that you’ve had some time with it, @sfox52 ?

 

[sfox52]

Doug, The 730 is sounding great in my office system. I had been using the SX-626 there. The HK is plenty for my NLA speakers, and the tuner is more sensitive and quieter than the Pioneer. I haven't tried the phono function yet, though I do have a turntable hooked up. Thanks again for the great work!

 

[JMiP]

Have you had a chance to update that one phono board yet?

 

[Skywatcher]

Doug, The 730 is sounding great in my office system. I had been using the SX-626 there. The HK is plenty for my NLA speakers, and the tuner is more sensitive and quieter than the Pioneer. I haven't tried the phono function yet, though I do have a turntable hooked up. Thanks again for the great work!

I also found the tuner in the 730 to be exceptional. And is much more "quiet" than most tuners out there making it not fatiguing at all. Of the last two I rebuilt, one of the owners came close to me not wanting to give it back. Makes me wish I owned one just for the tuner.

 

[dlucy]

Have you had a chance to update that one phono board yet?

I have a second 730 on the bench now and it is getting that phono stage mod.

 

[dlucy]

The phono stage getting 100% rebuilt and the RIAA/IEC mod

 

[JMiP]

Can you please work up a BOM for that whenever you get a chance? I bought phono board from someone on eBay and would like to do this some day.

 

[dlucy]

Here’s a visual depiction of the difference between a hk730 recapping... mild noise improvements... and full-on, dlucy-is-OCD, get-the-noise-out restoration.

 

[dlucy]

Can you please work up a BOM for that whenever you get a chance? I bought phono board from someone on eBay and would like to do this some day.

I'm finally getting time to post this. Here is the parts list I used when rebuilding the entire phono board and putting in the RIAA/IEC mod:

Component Qty Type Sub-type value 1 value 2 purpose mouser PN ​

C701,C702 2 Capacitor Electrolytic 22 uF 10 V signal 647-UKL1E220MDDANATA ​

C703,C704,C711,C712 4 Capacitor Ceramic 47 pF 50 V signal 810-FG28C0G1H470JNT0 ​

C705,C706 2 Capacitor Ceramic 3300 pF 50 V signal 810-FG28C0G1H332JNT0 ​

C707,C708 2 Capacitor Ceramic 0.012 uF 50 V signal 80-MMK5123J50J01TR18 ​

C709,C710 2 Capacitor Electrolytic 100 uF 10 V signal 647-UKL1A101MED1TD ​

C713,C714 2 Capacitor Electrolytic 22 uF 10 V signal 647-UKL1V220MEDANA (corrected from 33 uF)​

C715alt,C716alt 2 Capacitor Ceramic 0.33 uF 50 V signal 505-MKS2C033301C00MI ​

C717alt,C718alt 2 Capacitor Electrolytic 1 uF 35 V signal 505-MKS2C041001F00MI ​

C719,C720 2 Capacitor Electrolytic 1 uF 50 V signal 505-MKS2C041001F00MI ​

C721alt,C722alt 2 Capacitor Electrolytic 470 uF 25 V power 647-UPW1E471MPD ​

Q701,Q702 2 Transistor BJT 2SA872 ( E ) ECB signal 512-KSA992FTA ​

Q703,Q704,Q705,Q706 4 Transistor BJT 2SC1345 ( E ) BCE signal 512-KSC1845FTA ​

R_on_back_of_board 2 Resistor Carbon composition 5.6K 250 mW signal 71-CCF555K62FKE36 ​

R701,R702,R705,R706,R707,R708 6 Resistor Carbon composition 100K 250 mW signal 71-CCF55100KFKE36 ​

R703,R704,R727,R728,R733,R734 6 Resistor Carbon composition 220 R 250 mW signal 71-CCF55221RFKE36 ​

R709,R710,R715,R716 4 Resistor Carbon composition 330K 250 mW signal 71-CCF55-332K-E3 ​

R711,R712 2 Resistor Carbon composition 470 R 250 mW signal 71-CCF55475RFKE36 ​

R713,R714 2 Resistor Carbon composition 22K 250 mW signal 71-CCF55-22.1K-E3 ​

R717,R718 2 Resistor Carbon composition 3.9K 250 mW signal 71-CCF553K92FKE36 ​

R719,R720 2 Resistor Carbon composition 100 R 250 mW signal 71-CCF55100RFKE36 ​

R721,R722 2 Resistor Carbon composition 15K 250 mW signal 71-CCF5515K0FKE36 ​

R723,R724 2 Resistor Carbon composition 270K 250 mW signal 71-CCF55274KFKE36 ​

R725,R726 2 Resistor Carbon composition 120K 250 mW signal 71-CCF55121KFKE36 ​

R729,R730 2 Resistor Carbon composition 10K 250 mW signal 71-CCF5510K0FKE36 ​

R731,R732 2 Resistor Carbon composition 220K 250 mW signal 71-CCF55221KFKE36 ​

R735,R736 2 Resistor Carbon composition 680 R 250 mW signal 71-CCF55680RFKE36 ​

Before or original state:



Nudie:



After rebuilding:



Installed:



And I hope the owner will chime in and let us know how the recap, upgrades and phono EQ curve mods sound....

 

[Flounder]

And I hope the owner will chime in and let us know how the recap, upgrades and phono EQ curve mods sound....

Hey Doug. I'm hoping to spend some time with it this week, and I will definitely report back to the thread to let everyone know.