Odd Problem H/K 330B: Left Channel VERY Weak SOLVED

C524 to C523: No change.

C522 to C521: HELLO LEFT CHANNEL!

However. Left channel is thinner than the right - not as full sounding, not nearly as much bass. Hmm.

And - why did this happen? Both channels work now. It must have been a poor solder connection, which is strange. I did notice some light brown residue on the cap leads when I swapped them. I wonder what that residue could be and if it could be related to a bad solder connection.

Edit2: Swapped Q506 and Q505, maybe the channels evened out, maybe they were never uneven, or maybe it's all in my head. o_O Now I will listen for a while!
 
Last edited:
Alright, after listening, the left channel is thinner. Also, the CONTOUR switch has practically no effect on the left channel compared to the right.

When running a signal directly to the amp board, the channels are even.

I guess it's back into the tone control board & contour switch ... I probably messed something up. (Edit - it must be the tone board, since the tape out channels are even as far as I can tell.)
 
Last edited:
Johnny_Law said:
Looking at the circuit diagram, @dlucy, now it seems like the problem HAS to be C522, Q506, or C524. I think my next step will be to see if I can swap each for its equivalent in the right channel, one at a time, and see what happens.
Click to expand...

C522 and C524 are electrolytic caps, so you should replace them if you have not done so already. Swapping them for their counterparts in the other channel is a fine idea to determine if one of them is the cause. But replace both (and all the electrolytics) when you can.

C522 is a stage-coupling cap. Very common to find these in-between one stage or circuit and the next. These are GREAT places to switch to film caps, especially nice ones. For instance you could put in a 1uF 50V or 63V Panasonic ECQ series or WIMA MKP, MKS, FKP, or FKS series cap here and have slightly better audio performance.

Q506 is one of those notorious 2SC458 slope-faced transistors known to go bad or go noisy. Great idea to test it by swapping with its other-channel twin, but you're already planning to replace this with a KSC1845 I think.
 
Johnny_Law said:
Alright, after listening, the left channel is thinner. Also, the CONTOUR switch has practically no effect on the left channel compared to the right.

When running a signal directly to the amp board, the channels are even.

I guess it's back into the tone control board & contour switch ... I probably messed something up. (Edit - it must be the tone board, since the tape out channels are even as far as I can tell.)
Click to expand...

I highly recommend recapping and replacing the 2SC458 and 2SC871 transistors throughout the entire unit. You will be prone to marginal and failing component doing weird things to your performance. If you clear out these known problems, there is a good chance you'll have fewer mysteries left to solve.
 
Thanks Doug - that's the thing, they are all new. I used KSC1815 for the 2SC458s and new caps too.

In the meantime I took apart the Contour switch and cleaned it, no change.

When I was putting the board back in, however, I had kept the music playing. Was tightening a pot, and viola, full sound through the left channel! o_O

It appears something is making an intermittent connection - but I think it's somewhere inside the board. Some of the solder leads for the pots are partially lifted - but I've been jumping them fine. No change however. When I wiggle the pots on the board, or even just touch them, full sound goes in and out. Will keep poking at it and trying different things.

I wonder if it could be something inside the pots themselves, even though they measured OK before.
 
Well I managed one hell of a feat. Two of the lifted leads somehow got soldered to the wrong paths - which happened to be exposed - just barely touching. Which is why it kept going in and out.

Errant solder remedied, back in business, both channels behaving like they should.

I'll be listening to it as I redo the walnut veneer on the case, and hopefully will have a victorious picture to post soon. With some bourbon.

Thanks all for walking me through this ...

In sum: Problem was a bad solder connection of a capacitor on the control amp. Problem was compounded by user error bridging lifted leads on the tone board.
 
Too bad you didn't have a circuit tester or scope! You could have found the bad connection in less then an hour....
Glad to hear all is good tho! It will make the tunes sound that much better now right!?;)
 
Johnny_Law said:
Thanks Doug - that's the thing, they are all new. I used KSC1815 for the 2SC458s and new caps too.
Click to expand...

You used a KSC1815 instead of a KSC1845? Or was that a typo? What I remember is the 1815 is an OK replacement but isn't low noise audio frequency like the 1845.
 
The Fuxtor said:
Too bad you didn't have a circuit tester or scope! You could have found the bad connection in less then an hour....
Glad to hear all is good tho! It will make the tunes sound that much better now right!?;)
Click to expand...

Hmm... if you've got a link to how to use those to quickly diagnose this kind of problem, please post it. I've got plenty of tools and some decent amount of hobbyist experience, but I don't have a "how to" that would get to these answers as quick as you're suggesting. Please share.
 
Do you have a scope?? Otherwise I remember reading a web page on using a diy audio probe.
If using a scope, basically same process but you will "see " the audio signal instead of audible sounds!
 
dlucy said:
Hmm... if you've got a link to how to use those to quickly diagnose this kind of problem, please post it. I've got plenty of tools and some decent amount of hobbyist experience, but I don't have a "how to" that would get to these answers as quick as you're suggesting. Please share.
Click to expand...
See above!
 
Johnny_Law said:
I'll be listening to it as I redo the walnut veneer on the case, and hopefully will have a victorious picture to post soon. With some bourbon.
Click to expand...

Awesome! Make sure you post before and after photos. And a few of whichever bourbon you use.

If you ever get a hankering to learn wood working, the 330 series is relatively easy to make solid hardwood cabinets to replace the particleboard original one.

HK 330B cabinet mahogany 001.jpeg
HK 330B cabinet walnut 003.jpeg
 
dlucy said:
Awesome! Make sure you post before and after photos. And a few of whichever bourbon you use.

If you ever get a hankering to learn wood working, the 330 series is relatively easy to make solid hardwood cabinets to replace the particleboard original one.
Click to expand...

Those look fantastic - woodworking is next on my to-learn list, problem is I need more garage space. But it's a bit ironic, some things taking up that space are stuck there needing woodwork (McIntosh ML-2Cs in need of front baffles, JBL C40 cabinets in need of structural work and veneer, ads L1230 cabinets in need of risers, Velodyne ULD-15 in need of top water damage repair) ... our resident Dr. Biggles has graciously offered to show me how to use a router. I still need to take him up on that kind offer!
 
Johnny_Law said:
Sounding awesome. Happy camper! Cheers everyone :beerchug:

rOxlGkRl.jpg
Click to expand...

Look at great! If you find the sound isn't warm enough or tube-like enough you might try Basil Hayden instead of Maker's Mark. ;)
 
Well, the victory was short-lived, as this morning I decided to spin a record after listening via AUX last night.

Guess what? No left channel. :rflmao:

I suppose I should have rebuilt the Equalizer board (and radio boards) while I was doing the others. Ah well. Next step is to get new components ordered which I will do tonight / tomorrow!

Oh yeah, and maybe I'll find some of that Basil Hayden to celebrate listening to vinyl on it. :king:
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom