• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

HK 730 Separating Heatsink from Amp Board

xrayspex77

xrayspex77

Super Member
My HK730 has a 40VDC (at Speaker Terminal) Spike in the L Channel when powering On. After about 5 mins it will settle to around 100mV. If I power off/on the spike is minimal. Discovered that unplugged I get 8VDC at the L Terminal until whatever Cap it pulling from is drained. R Channel is Good
Found these threads with similar issues

http://audiokarma.org/forums/index.php?threads/harmon-kardon-730-high-dc-offset.552435/

http://audiokarma.org/forums/index.php?threads/harman-kardon-730-issues.416189/

http://www.audiokarma.org/forums/index.php?threads/left-channel-issues-with-hk-730.372163/

I am going to recap the Amp Board and check the Trans in the L Channel. I have the subs suggested
(30) KSC1845FTA's (they don't seem to make the EBU's anymore) to match up for the 2SC1400's
MJE243G for the 2SD415
MJE253G for the 2SB549

I have removed the Heatsink/Amp Board which was easy.
Is removing the Heatsink from the Amp Board is as easy as removing the screws from the OP Trans or do I need to desolder the Legs from the Amp Board?
Thought I'd ask before I found the hardest way to do this, might save another relative noob some time
 
Register to hide this ad
Partly answered my own question. Removing the screws from the Output Transistors did allow me to separate the Heatsink from the Amp Board. For anybody else trying this, it would be a good idea to have Thermal Grease handy when reassembling.
Now to start testing
 
on my 730 i had to replace the transistors along with the caps to get it working properly.
 
Thanks, there seems to be a lot of threads about the 730 and these issues. I'm just trying what others have tried.
Realized too late that I didn't have the right Caps so I went ahead and replaced Q402/404/406 which brought the DC down to a respectable level after the 40VDC Spike.
I think it has to be at least partially Cap related, after it settles down to reasonable DC if I turn it off/on there's no spike but I don't know enough to know why.
Will order Caps and more Thermal Grease and try again.
 
I've recapped the Left Channel of the Amp and the first couple of power On's I still got the 40VDC spike. From another thread
http://audiokarma.org/forums/index....me-drop-with-speakers-on.291863/#post-3599317
I decided to pull the jumpers to see if it might be the PreAmp. Ran the Tape out from another Receiver to the Main In and the spike was 3.5V and dropped quickly to about 5mV.
I DeOx'd the Main/Pre Jacks and put the jumpers back in and the spike stayed gone so I don't know if the new Caps took a little while to settle in or it was related to the jumpers.
Will test it in the morning with a sacrificial speaker
 
Tried it with "The Wold's Most Advanced Air Suspension Speaker" (Mongomery Ward junkers) in System 1/A with my MM in system 2/B. No spike so I moved it back to, hooked it up and as soon as I pressed the button for System 1/A got static pop and it blew the 2 fuses for the Left PS. The R Channel was good ( and the speakers are OK). I got some more fuses today and with only the MM in the speaker terminals the 40VDC spike is back.
It goes from 0 to 40VDC from 4 - 8 secs after power On and after about 1 min the DC has settled to around 10mV.
If I power off/on after it warms up, no spike.
Powered off (i'm guessing its draining the PS Caps) the VDC climbs to 43VDC after about 3 mins and then drops off.
It does seem to be the Amp, I pulled the Jumpers to the PreAmp and still got the Spike.
I haven't replaced the 2SD415's and 2SB549's but I'm just going by what people have tried in other threads so I'm at a loss.
It does seem to be something that's not closing when it should but I don't know where the delay/slow start circuit is.
I thought it might be Q406 (Q405 R) but that's new as well as the Cap.
Resistor?
Anybody have an idea?
 
Replaced Q408 & Q412 and so far its sounding good :) No Static, no Pops. The L Channel comes on after about 4 secs, the R about 2 secs later but I'm guessing that's the new components. There is a 6 - 9V spike at Power On but happens during the Delay/Slow start and is not audible. I'll test it for a couple of days before I put it back this time and if it remains fixed this time I'll recap the R Channel over the winter.

Thanks to everyone who contributed to the Threads I used followed to fix this
 
You must log in or register to reply here.
Back
Top Bottom