Vintage Asylum

Posted by dogwan (A) on June 27, 2012 at 18:54:14

In Reply to: RE: All for want of a fuse-holder cap! (HK 800+ rcvr) posted by dogwan on June 27, 2012 at 18:21:48

Summed up from another thread over on AK

"Recently picked up an abused Harmon/Kardon 800+ quad receiver from CL for $20. Seller was a nice old gent who was a scrounger and knew very little other than it powered on and was missing fuse caps for 2/4 (right side) of the speaker lines.

After a few weeks of it sitting just inside the front door I finally got around to checking it out and couldn't get any power. Upon opening it up I found that someone had done some serious hacking. One of the transformers (I picked this up because of the twin power supply) has been clipped. The main power fuse holder was broken and electrical taped back together. The leads to the fuse holder were broken and twisted back on without solder. Oy vey!

Other than that I haven't done much exploring. I surmise that something happened to one of the channels and it probably kept blowing fuses. Whoever hacked it probably just cut that transformer and used the other side {L-front and back} as {left and right}.

The reason I grabbed this is because aside from all the extra quad circuitry there is a dedicated switch to keep it in 2 channel mode at 55w/ch with the twin power supply.

This weekend I went in and DeOxit'd all controls, downloaded the service manual, and replaced the busted PS fuse holder.

After rewiring the clipped transformer I slowly brought it up on a Variac while constantly checking the voltages on the transformer secondaries and comparing the two transformers. I kept a very close eye on the one that had the primary leads clipped. Got all the way up to full line voltage with no abnormalities.

Next I checked and adjusted the DC offset. Then I plugged an Ipod into the aux. and then plugged in a pair of beater headphones ..... AND got glorious sound!

Then I ran it using headphones only in ever increasing lengths of time with cool down periods. The next day when I was confident everything was stable I hooked it up to some speakers and ......NO sound!

Well, here's where it gets interesting. On Saturday I stumbled across an HK 100+ receiver on CL for $25 which I picked up thinking I could use it for spare parts if needed. After getting frustrated not being able to figure out why the 800+ would output sound on the headphones, but not speakers I set it aside and played with the 100+.

It was only while playing with the 100+ did I come to find out that even when switched into 2-channel "stereo" mode it still needed fuses in both the front and back speakers for the front speakers to work. I speculate that the fuses are in series before the 4 amp sections are summed into 2 channels.

Now the frustrating part is they used different fuse holders from the 100 to the 800 series amps. So now I am one lousy fuse screw on cap away from a full test! AND it's a metric size!

It should be fun comparing the sound signature of the two receivers when I get them both up and running."

-Dogwan