The ultimate HK 900+ restoration

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deanrantala

New member
Joined
Nov 10, 2022
Messages
9
Location
Denver, Colorado
I already posted a couple questions leading up to this, it is now time to officially move forward - and I figured I would start a new thread.

I really hope 4morhktech is still around and can chime in with any useful info I may be missing here.

First... the current condition looks a bit worse than it is, but here are some shots....

The front-side.. The tuner knob is not original - I realized this after looking at photos of other 900+ units online. The donor unit has an original knob, which will be moved over to this unit when it is re-assembled.
PXL_20221112_235126323.jpg


The wood grain case is pretty clean after 40+ years:
PXL_20221112_235130505.jpg


The back... years ago, I cut a section out of the back and inserted the red-black RCA jacks you see there. I did this in order to add pre-amp out / amp in jacks for some speakers I had bi-amped at one time. Luckily, the donor unit has a mint back-panel - and I will be un-doing this mod in order to return the unit to original condition.
PXL_20221112_235145986.jpg


Top side
PXL_20221112_235512399.jpg


The CD-4 board (also the phono pre-amp)
PXL_20221112_235527782.jpg


The bottom side:
PXL_20221112_235542038.jpg
 
I got the capacitor list together.

Now, this list includes a few extra of each for most the values (in case one gets damaged, etc).

I am also breaking this list down into 2 parts... audio-grade and normal high-temp. The entire analog audio path (Tone board, amps, inverter, SQM board, CD-4 board) will be completely re-capped with Nichicon UFG (fine gold) series capacitors. The power supply, FM and AM boards will use normal high-temp rated Nichicon caps.

For the AM/FM boards, I found an assortment on FleaBay that had all the capacitors needed in a single lot. It was a generic "nichicon capacitor assortment" lot and nothing specific to this unit.

I tried creating this list via the HTML editor here, but it just is too much hassle... Going to just share the link to my Mouser shopping cart..

https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=515fd58e05
That includes all capacitors needed except for AM/FM section.

Actually.... there are 4 additional capacitors (on the CD-4 board) that are not included here (I already had):
.15uF (x2)
.68uF (x2)

Other than that, what is in the cart will re-cap this entire stereo.

I took special care to ensure the voltages were the same or higher. I also measured the available space for each capacitor and compared it to the physical size of the new capacitors to ensure they would fit correctly.

This stereo has a few axial-lead style capacitors (one lead on each end of the capacitor). Since these are becoming hard to find, I ordered standard radial-lead capacitors and will solder one leg into the original hole and attach the OTHER lead with a jumper wire. The capacitor can then be secured with electrical grade silicone.
 
Is there going to be any follow up on this? Just got myself one of these and would be nice to see what needs to be done and how. Cheers
 
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