• 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

Onkyo tx-4500mkII volume pot accident

Chriswashere

Chriswashere

Active Member
I've been playing with audio for a few years now, and a really strange thing happened. So I have this barn find onkyo tx-4500mkii I was about to power up on a variac to see what it would do, so I got everything hooked up and ready to go. So at this point I had already played with the controls a bit, so I just compulsively moved the volume knob back and forth, which is habit for any of us who have to clean any controls. While doing this the volume pot just froze dead, which was odd. Suddenly the staff just broke off the control. What on earth happened here?

What makes it worse is not only can I not find an affordable replacement, all the voltages seem to be fine in this unit. I have no idea why it was taken apart in the first place and put in storage, but due to the disconnected tuner it seems like someone was trying to clean the push buttons.
 
Register to hide this ad
You Monster! No just kidding, maybe a modern equivalent stereo pot could still be sourced. The bay sometimes has doner units and ones stripped and being parted out. The tuning piece would be the difficult one with the touch sensitive portion.
 
Man I feel like a monster. I've been looking on eBay and haven't seen anything that'll do the job. There is an original, but it's close for $40 and I'm not about that. Not for a barn find anyways.

I have a 200k pot from a layfette with a different staff I was going to install for test purposes just to see if this thing is dead if not, which it probably is.

As for the tuner, it's a mess. Hopefully it'll work again but in all the years I've been doing this I've never had to restring a tuner. Or should I say rebuild.
 
Yeah, I don't dig restringing tuners either. I relamped my TX4500 and skipped the dial indicator for that reason. The hardest thing about the volume pot will likely be getting the specific shaft dimensions needed. Seems most brands used a smallish group of similar resistance values available from the manufacturers, I assume it would also be a log pot. Schematics for MkII should be available on line I would think. Were you able to get broken piece out of the knob?
 
really it may be best to just find a parts unit or something. I've heard talk of rebuilding this control if a new shaft can be found, but I don't know exactly why this pot did what it did.

Later I'll just throw that 200k ohm pot in if it fits and go from there. If the unit has life then replacing that bad pot will be the priority.

Luckily I got the parts out of the knob, but if I keep the layfette control in, I'll have to use a different knob which is no good, but with this being a barn find all it really is is an experiment.
 
$40 doesn't seem to be a lot of money to get a well respected receiver repaired properly. Hacking it up to save a few bucks just seems wrong. I assume you got it cheap so why not fix it right?
 
paid 35usd for my sta-2300 mono stereo switch board. paid $655 for unit from rat shack.. on sale orig. msrp was about 799. If you wanted to buy my 2300 serviced and all works well. Like a Ferrari? the price of the unit doesn't depreciate.

buy the damned thing.. support the guy who took it out.
 
Last edited:
Sriskie said:
$40 doesn't seem to be a lot of money to get a well respected receiver repaired properly. Hacking it up to save a few bucks just seems wrong. I assume you got it cheap so why not fix it right?
Click to expand...
I would also bite the bullet and get the original part. It is often very hard to find a suitable replacement that will fit properly, even if the original is expensive it will save you a lot of time, and time is money too.
The unit still is what it is whether it was a barn find or not.
 
Well, my reasoning for not paying the $40 is that this thing has sat outside for over 20 years, and the fact that it even shows signs of life is amazing. So before even attempting to fix it right, I was to put some cheap parts in it just to see what all it can do, if anything. If I didn't have it taken apart i'd show some pictures of how bad it really is.
 
Chriswashere said:
Well, my reasoning for not paying the $40 is that this thing has sat outside for over 20 years, and the fact that it even shows signs of life is amazing. So before even attempting to fix it right, I was to put some cheap parts in it just to see what all it can do, if anything. If I didn't have it taken apart i'd show some pictures of how bad it really is.
Click to expand...
I there enough of the old shaft to grab and turn it with pliers? If you spray some faderlube into it you might be able to work it loose gently and test.
 
The old shaft is toast sadly. There was apparently some deep corrosion in the pot that wrecked it. BUT, I put in the pot from the layfette and its somehow alive. Both channels seem to be doing okay despite the dirty controls. This is absolutely amazing honestly.

The only issue is a slight hum in the background, which is the same issue my onkyo tx-670 is having.
 
Another issue; In order to get the left channel to come on, I have to turn the volume way up to get it to play. Once it does play, I can turn the volume back down and it'll keep playing.
 
Chriswashere said:
Another issue; In order to get the left channel to come on, I have to turn the volume way up to get it to play. Once it does play, I can turn the volume back down and it'll keep playing.
Click to expand...
That's probably the relay. It could also be a dirty pot or switch if you haven't cleaned them.

Tap the relay and see if it cuts in and out.
 
Hum is not surprising to have, likely the big filter caps need replaced by now. I just had to do that with mine. It hummed loudly and once done has quieted down tremendously. Your MkII uses two separate caps already, I had to convert mine from a single multi cap to two caps like yours. I used two appropriate Nichicon's from Mouser.
 
Thanks you, the relay is the issue. How do I clean that?

The filter caps are a concern, but I've never had a any cause a hum like this. Is there a way to isolate the issue back to these caps? It is a little odd that I have 2 humming onkyo units though.
 
Chriswashere said:
Thanks you, the relay is the issue. How do I clean that?

The filter caps are a concern, but I've never had a any cause a hum like this. Is there a way to isolate the issue back to these caps? It is a little odd that I have 2 humming onkyo units though.
Click to expand...
I normally take it apart and polish the contacts with brasso, then clean it away with a non-residue contact cleaner.

The hum could also be caused by other caps in the power supply. Do you see any signs of leakage?
 
I took it apart and cleaned it and it's far better. The next issue was cold joints for the rca jacks, so I fixed those. Also the rca connectors being heavily corroded caused issues which have also been fixed. It's been playing fone on a variac (at 50v AC rn for safety), and it's been doing really good as far as I can tell.


Nope, not seeing any signs of leaking in either onkyo.

Tomorrow I might get the guts to repair the tuning section in this thing. We'll see though.
 
Power supply basically is converting the AC voltage into the plus and minus D.C. rail voltages. At it's most basic it does it with the transformer, rectifier and filler caps. If either one of the filter caps is drying out the unit is prone to hum. There are other types of hum, but for a very old receiver that is the first box to check off.
 
You must log in or register to reply here.
Back
Top Bottom