• 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

What's the weirdest factory mistake you've found?

Raccoon1400

Raccoon1400

Super Member
This one had me scratching my head. I just finished restoring a Luxman L-100 and I noticed the bass was being cut when I engaged the tone section. I could even it out by turning the bass up to about 3-4 o'clock. I messed around for almost 2 hours trying to figure out what could be causing this. I checked my work over multiple times. I observed the problem on the scope.
I found the bass control was a log pot when it should be a linear pot. Meaning the halfway point was at 3-4 o'clock. At this point it was well past my bed time so I called it here.

In the morning I remembered another thing. The volume control was very sensitive. Even with the attenuator all the way down, the first notch was almost normal listening levels. I decided to check if this was a linear pot. And it was! (and it was the same value as the bass pot) And although this unit appeared to have been worked on before (someone soldered all the molex connectors), the soldering on these pots appeared to be factory.

So someone at the factory mixed up the bass and volume pots? I switched them back and now have a properly functioning bass control, and a properly functioning volume control.

This also shows the importance of sleeping on a problem. It wasn't until the next morning I thought to check if the volume pot was correct. I'm kind of impressed I caught this.

So, what is the weirdest factory mistake you've found?
 
Register to hide this ad
Raccoon1400 said:
This one had me scratching my head. I just finished restoring a Luxman L-100 and I noticed the bass was being cut when I engaged the tone section. I could even it out by turning the bass up to about 3-4 o'clock. I messed around for almost 2 hours trying to figure out what could be causing this. I checked my work over multiple times. I observed the problem on the scope.
I found the bass control was a log pot when it should be a linear pot. Meaning the halfway point was at 3-4 o'clock. At this point it was well past my bed time so I called it here.

In the morning I remembered another thing. The volume control was very sensitive. Even with the attenuator all the way down, the first notch was almost normal listening levels. I decided to check if this was a linear pot. And it was! (and it was the same value as the bass pot) And although this unit appeared to have been worked on before (someone soldered all the molex connectors), the soldering on these pots appeared to be factory.

So someone at the factory mixed up the bass and volume pots? I switched them back and now have a properly functioning bass control, and a properly functioning volume control.

This also shows the importance of sleeping on a problem. It wasn't until the next morning I thought to check if the volume pot was correct. I'm kind of impressed I caught this.

So, what is the weirdest factory mistake you've found?
Click to expand...

Good catch.
 
A few years ago, I could not find the cause for intermittent power in a NAD unit. Turned out that the power cord ends inside it were never soldered. So sometimes it powered on and sometimes it didn't. I figured it must have been problematic for someone for a very long time.
 
Raccoon1400 said:
This one had me scratching my head. I just finished restoring a Luxman L-100 and I noticed the bass was being cut when I engaged the tone section. I could even it out by turning the bass up to about 3-4 o'clock. I messed around for almost 2 hours trying to figure out what could be causing this. I checked my work over multiple times. I observed the problem on the scope.
I found the bass control was a log pot when it should be a linear pot. Meaning the halfway point was at 3-4 o'clock. At this point it was well past my bed time so I called it here.

In the morning I remembered another thing. The volume control was very sensitive. Even with the attenuator all the way down, the first notch was almost normal listening levels. I decided to check if this was a linear pot. And it was! (and it was the same value as the bass pot) And although this unit appeared to have been worked on before (someone soldered all the molex connectors), the soldering on these pots appeared to be factory.

So someone at the factory mixed up the bass and volume pots? I switched them back and now have a properly functioning bass control, and a properly functioning volume control.

This also shows the importance of sleeping on a problem. It wasn't until the next morning I thought to check if the volume pot was correct. I'm kind of impressed I caught this.

So, what is the weirdest factory mistake you've found?
Click to expand...
This happens, more than you would think. Especially, linear pots put into volume control sections. Units get full blast, at 9:00 O'Clock position.

Same resistance audio (logarithmic) pot, volume range is normal again.

:thumbsup:
 
That's a great catch. I don't think I would have caught that one.

Weirdest one for me - that was simple enough for me to find - was a fellow ak member's Martin Logans he'd acquired. He noted the bass wasn't all there. We determined that one woofer wasn't working and assumed the woofer was blown.

But, the woofer tested fine. Looking at the crossover ... lo and behold one of the wires that was supposed to connect the circuit board to the woofer wasn't soldered onto the board. At all. It was bone dry of solder, clearly a woopsie at the factory. I soldered it and viola, woofer stared working! I wonder how disappointed the original owner must have been with the bass!
 
Last edited:
I bought a Marantz model 140 power amp years ago before prices became insane. The meters didn't light up even with new fuse lamps. It came to me in the original sales carton with all the original packing and paperwork. That was inside the original shipping box. The amp looked brand new. Not a smudge on it. My guess it was returned due to the meters not lighting up and never got sent back for repair. I found that the wires that went to the fuse lamp holders hadnt been soldered in place. It was super simple and fix though. The outer box had the stereo store's name and address stamped on it. It was a shop in Colorado.
 
elnaldo said:
I've seen a unit (Deltalab Effectron 2), all you will find on the internet is people commenting about how noisy those units are, and all kind of problems they developed. Well, all the electrolytics (with exception of 2) were placed backwards from factory.
Click to expand...
Was the polarity silk screened backwards on the PCB, and the ensembles pit them in according to what they saw printed on them? Thats just really an odd one for sure.
 
When I worked for Fretter doing their audio servicing, I worked on a store stock Sony CD player that was inoperative. I found a transistor was installed backwards. It could never have worked, which told me that Sony did not final test their products. This was in the 1990's and I think their quality has improved since then.
 
62vauxhall said:
A few years ago, I could not find the cause for intermittent power in a NAD unit. Turned out that the power cord ends inside it were never soldered. So sometimes it powered on and sometimes it didn't. I figured it must have been problematic for someone for a very long time.
Click to expand...
I had a similar one in a Marantz receiver. One wire was formed to an AC socket but never soldered. Also found a 0.001uF where a 40pF was supposed to be. That's not so weird though.

In a '66 Mustang we had, it became intermittent, and would just die while cruising down the road. It would eventually restart. Turns out a jumper wire assembly that was there to be removed for putting in a tach had never been crimped on one end!
 
I've formed the view that Tim De Paravicini's amplifier designs were a mistake. Here is one of his monstrosities.

Remains of a capacitor fire.

1703393026236.png

Valves warping under atmospheric pressure as the glass softens (circa 1250 degrees)

1703393026284.png

Green ceramic resistors melted into a blob

1703393026342.png

The guy's lucky it didn't burn his house down.
 
Last edited:
I had a Sansui 890db in here recently that had one channel out in just phono 2. Turned out there was a bridged solder connection on the ribbon cable that was soldered to the input jacks. Looked to be factory. It took me a bit longer than it should have to find that.

Every time I get stuck on some weird problem and feel like I'm bad at my job (I do this full time) I'm going to have to remind myself I figured out that these two pots were switched!
 
It was a cold morning and the security guards at the airport baggage screening area were shivering at their post. What appeared to be a new portable space heater sat nearby, unused. I asked why they weren't using it and they said it didn't work. I said I'd take a look at it and took it to the Avionics bench. After disassembly, I discovered the circuit board had a resistor with one leg which was never soldered onto the board. Soldered the leg back on and returned the now working space heater to the happy (and now warm!) security guards.
 
elnaldo said:
I've seen a unit (Deltalab Effectron 2), all you will find on the internet is people commenting about how noisy those units are, and all kind of problems they developed. Well, all the electrolytics (with exception of 2) were placed backwards from factory.
Click to expand...
Very interesting. Here's some comments from people selling their Effectrons, "They're not the warmest sounding...it's is a quirky, entertaining device with lots of character...also capable of some pretty wild and weird sounds". Could the backwards caps been the cause for their "sales pitch"? :dunno:
 
Raccoon1400 said:
And although this unit appeared to have been worked on before (someone soldered all the molex connectors), the soldering on these pots appeared to be factory.
Click to expand...
You're just assuming that the soldering was done by the factory. Maybe someone just had better soldering skills than the common tinkerer.
 
eiraved said:
It was a cold morning and the security guards at the airport baggage screening area were shivering at their post. What appeared to be a new portable space heater sat nearby, unused. I asked why they weren't using it and they said it didn't work. I said I'd take a look at it and took it to the Avionics bench. After disassembly, I discovered the circuit board had a resistor with one leg which was never soldered onto the board. Soldered the leg back on and returned the now working space heater to the happy (and now warm!) security guards.
Click to expand...
It's a good thing that you kept those security guards warm while they huddled around that heater all day. Probably prevented a terrorist attack.
 
You must log in or register to reply here.
Back
Top Bottom