Meanwhile in the west, most people wouldn't bother to stop and pick up 30 cents on the road. 30 cents would be the average shop labour price for 20 seconds!
Not a repair but a modification: turned off the DC Booster circuit in a Behringer UMC202HD audio interface for less interference and IMD.
I fixed our Miele dishwasher last week. Obtained as a "giveaway" six or seven years ago, it's probably 15 by now. Twas leaking from it's side and tripping a fault code. After much gnashing of teeth I was able to remove the side panel. There was a sensor pipe entering the wash compartment. The sealing grommet had perished and water was sprayed out during wash cycles. Luckily I had a tube of high temp silicone, with a little squirt, it was fixed. Been fine so far. I will do anything to not have to wash the dishes in the sink again!
Oh how I love technology..
Oh how I love technology..
Working on a DCC model railway controller.
Updated software to cope with 4 digit addressing of loco's.
Fixed it and sent it out.
Built up another and tested it then spotted one of modes only does 3 digits and not 4 digits ! whoops....
Easy fix but once they are out there its not so easy to fix.
Updated software to cope with 4 digit addressing of loco's.
Fixed it and sent it out.
Built up another and tested it then spotted one of modes only does 3 digits and not 4 digits ! whoops....
Easy fix but once they are out there its not so easy to fix.
And how you‘re supposed to get rig of the hum….
Attachments
Built up a transistor matcher and curve tracer.
N channel devices worked great.
P channel devices just showed zero volts all along the curve.
Followed signal into differential amplifier and got zero volts out.
Strange inverting input was stuck at -12 volts.
So got pcb on screen and followed pin 9.
It went out to a 100pf capacitor and next that was a track which was -12 volt line.
Then spotted cap pad was shorted to via on -12 volt line.
N channel devices worked great.
P channel devices just showed zero volts all along the curve.
Followed signal into differential amplifier and got zero volts out.
Strange inverting input was stuck at -12 volts.
So got pcb on screen and followed pin 9.
It went out to a 100pf capacitor and next that was a track which was -12 volt line.
Then spotted cap pad was shorted to via on -12 volt line.
A couple of weeks ago I fixed the vacuum cleaner by swapping the motor with an older one. Months ago I fixed the pcb of my bosch washmachine, by replacing a burnt resistor (it literally had a hole), a cap and the tiny SMD regulator powering the whole appliance. Now I have to deal with be beloved Adcom GFA-555MkII which started emitting strange noises out of the speakers. At least, once disconnected I couldn't measure any DC to the speakers...
Oh I know LOL
It didn't even fix the hum - it just moved the loop elsewhere. Today will be a rewiring session to find the hum.
When the power amp is on but not connected there is silence. When the power amp connects to the preamp there is a buzz which mostly goes away and is replaced by a hiss when the tubes get hot. Today, I chase down the issue in the preamp.
”Buzz”, as opposed to a “hum”? Which goes away when warmed up…. you may be chasing a load dependent power supply issue in the preamp.
Hum is mainly sine, buzz is more saw wave...
I'm going to move the power supply external and see how that is, otherwise my next build will use HV transformers. I have a feeling the "hiss" is really an RF oscillation somewhere but my scope isn't good enough to lock onto it.
Another idea I might try is using a 12V battery in place of the transformer/diodes.
Maybe I'm unrealistic, but I want the system to be powered up and silent. Not at full blast or anything, but if there is nothing playing and the system is at a reasonable level, it should be silent IMHO.
I can hear a quartz clock ticking on the wall 10 feet behind me, and that annoys me, too LOL
I'm going to move the power supply external and see how that is, otherwise my next build will use HV transformers. I have a feeling the "hiss" is really an RF oscillation somewhere but my scope isn't good enough to lock onto it.
Another idea I might try is using a 12V battery in place of the transformer/diodes.
Maybe I'm unrealistic, but I want the system to be powered up and silent. Not at full blast or anything, but if there is nothing playing and the system is at a reasonable level, it should be silent IMHO.
I can hear a quartz clock ticking on the wall 10 feet behind me, and that annoys me, too LOL
Ok. Progress. The hiss fades away after about a minute when the tubes are actually warmed up... There's an oscillation though. Time to get out the shielded cable...
If you are suspecting RF oscillation, maybe you‘ve got rectifiers in need of snubbering. Buzz can be RF oscillation gated on and off at a 120 Hz rate and may not even show up on the scope. It may be present under light load and gone under heavy load (or vice versa, or vice vice, or versa versa). Whether or not there is enough damping does depend on the load.
No. The DC comes from a DC-DC board that operates at 35kHz... It's only on the right channel - the last time I has this issue it was a simple wire dressing issue.
I think I also used twisted #22 instead of shielded cable, too... Gotta open it up to remember what I did.
You should hear the noise I get if I use an RCA cable as an antenna (connected to the amp but floating)!
Side question - When using shielded cable, I know you only connect shield to ground at one end, but which end? The RCA jack or the grid?
Found a disconnected signal ground on the oscillating channel. Fingers crossed that's the issue.
I think I also used twisted #22 instead of shielded cable, too... Gotta open it up to remember what I did.
You should hear the noise I get if I use an RCA cable as an antenna (connected to the amp but floating)!
Side question - When using shielded cable, I know you only connect shield to ground at one end, but which end? The RCA jack or the grid?
Found a disconnected signal ground on the oscillating channel. Fingers crossed that's the issue.
Ok. Some noise was coming from the computer by coax S/PDIF. That's now optical and sorted. Stupid loops LOL
EDIT: Most remaining noise was only there if the CD player was connected and grounded. Lifting the player's ground sorted the HF noise. It wasn't powered on and the input was not selected. Just RF/HF Gremlins running around in here.
EDIT: Most remaining noise was only there if the CD player was connected and grounded. Lifting the player's ground sorted the HF noise. It wasn't powered on and the input was not selected. Just RF/HF Gremlins running around in here.
Last edited:
Then you‘ve got noise running around all over the place - like trying to watch over the air TV in the room next to a server farm. Getting a clear picture was a pipe dream, even for a station 20 miles away. One of the 35kHz harmonics could be beating against something else, producing yet still more frequencies which might not have adequate filtering.
Some software in a DCC model railway controller.
The first 7 seg LED display wasnt showing correct segments.
It was a silly in the end.
I use bit set for segment on and then xor data with 255 to invert all bits for common anode.
I had accidentally hit & instead of ^ and it was anding instead of xoring.
The two keys are right next to each other hence the mistake.
The first 7 seg LED display wasnt showing correct segments.
It was a silly in the end.
I use bit set for segment on and then xor data with 255 to invert all bits for common anode.
I had accidentally hit & instead of ^ and it was anding instead of xoring.
The two keys are right next to each other hence the mistake.
Fixed the main hum issue - The main power circuit ground was using a chassis ground (I forgot the copper strap when I built it). Now the hum is low enough that you need to put your ear to the cone to hear it faintly. I can live with that. My tinnitus is louder than the SNR now.
This is what you get when you try to connect 9 amps, cassette, minidisc, tuner, phono, equalizer loop, 4 sets of speakers, 2 DACs, and bluetooth together in one unbalanced system. Frankly, I'm surprised it works this well.
This is what you get when you try to connect 9 amps, cassette, minidisc, tuner, phono, equalizer loop, 4 sets of speakers, 2 DACs, and bluetooth together in one unbalanced system. Frankly, I'm surprised it works this well.