Semiconductor Sources

Stopping a startup or shutdown spurious noise in the speakers is solved by turning off the speakers at those times or installing a speaker protection circuit.
 
NnionzngEMF said:
I was also wondering about what can be done to get filter the small voltage spike that is a noise and maybe a .25mV DC spike in the speaker outs too when I turn on. Would that be from the caps bad also or something totally unrelated?
Click to expand...

The slight buzz/thump at power-on is almost unavoidable with an amplifier lacking a speaker/protection relay. Many smaller units such as this exhibit this behavior normally. Turn the volume to zero before powering on, or get in the habit of turning to zero before powering down.
 
dlucy said:
For me, I always start with the power supply and reassure myself that it is providing the various B1, B2, B3, etc. output power that all the other boards need. If not, the other boards will ever measure out correctly.
Click to expand...

Thanks for the advice.

dlucy said:
I most times rebuild most/all of the power supply, but that's more from OCD than anything practical.
Click to expand...

I get that way in regards to researching... not always with hands on. :)

dlucy said:
Sounds like your transformer is operating. So, your main amp should be expecting a dual rail supply at +30 and -30 (or a single rail around +60) from the 30v 0v 30v wires on the power transformers secondary. And the single 18v secondary will end up supplying 13-15 v to all the othe r boards (or sometimes lower).
Click to expand...

Great, thanks for the affirmation. I need that from someone with experience.

dlucy said:
I didn't follow your powe supply output reasons. Does each of the 2 to 4 outputs measure as the schematic indicates? Anything 10% or more lower than schematic figure for that output?
Click to expand...

You lost me on this one... I think grammar can clarify. Let's see if I can translate... Nothing measures lower than schematic other than the:
"D58 was reading 00.6VAC and on the anode side 0VDC. Lucky charms ain't fixin that. :D"

Per the schematic on the Cathode is where I thought was weird since 0.6VAC (maybe the bad diode is doing) and the Anode 0VDC. That diode in circuit measures like open at first then the bias voltage reading. Weird, unless something like a transistor is charging a capacitor or something. Seems like a Zener though isn't supposed to be a Zener per the schematic. That rail is supposed to be per the schematic 22VDC past that Cathode. I'll check the capacitor just past that also... a 1000uF 25V cap in between the + and - ~20-22V rails (per schematic -19.7V (off D57) and 22V DC (off D58)) and the -19.7V DC has a 330uF cap in between the 38.5VDC bridge rectified + rail.

I also found there is a similar conducting to ground ~-2.5VDC in the adhesive that is dried up at the 330uF 25V and the 1000uF 25V positions. Even though D57 is closer to those caps... maybe electrolyte leaked to the D58. Not sure however.

dlucy said:
I have never thought to measure the conductivity of a large cap's glue as I always, always replace them. Its a good idea, though, and any of those globs of glue that measure any kind of voltage would push me to pull and replace them.
Click to expand...

Thanks again... this is my first stereo repair. I have some of the thermal silicone white stuff that I see in the salvaged TV's I've repaired or re-purposed for parts.
 
Watthour said:
The slight buzz/thump at power-on is almost unavoidable with an amplifier lacking a speaker/protection relay. Many smaller units such as this exhibit this behavior normally. Turn the volume to zero before powering on, or get in the habit of turning to zero before powering down.
Click to expand...

Will do and have been doing. Surprised to see on the voltmeter... then settles down to 0.02mVDC... goes negative about that after turning off.

Will something like a decoupling capacitor to decouple the DC prevent that or maybe like an isolation transformer modded in since seems both would decouple the DC?

Guessing something with the older transistors does this, any ideas? Thanks
 
NnionzngEMF said:
Adding reference to the Diode spreadsheet:
https://drive.google.com/open?id=1ThedZJ-b9v9D4afCVwwTlTxLwj0ykZ-b

Adding a reference to the IC/Transistor spreadsheet:
https://drive.google.com/open?id=1-MPApckHfQfO3S1JFn6c-q_8_wwRjNs9

Note: These are works in progress and need updating, verification and formatting. The link will remain the same and are made with Libre Office. Calc.
Click to expand...

When I try to follow your links here on my iPhone, Chrome pops up to handle the URL, then launches Googl Drive and that tells me I don't have permission to access it. I am properly logged in to my Google account at the time.
 
dlucy said:
When I try to follow your links here on my iPhone, Chrome pops up to handle the URL, then launches Googl Drive and that tells me I don't have permission to access it. I am properly logged in to my Google account at the time.
Click to expand...

I just logged out and checked the links. Working from a laptop not logged into Google. The file is in an .ods format and I'm thinking the Chrome browser can handle the file extension to view. Other than that, I am not sure at the moment.
 
dlucy said:
When I try to follow your links here on my iPhone, Chrome pops up to handle the URL, then launches Googl Drive and that tells me I don't have permission to access it. I am properly logged in to my Google account at the time.
Click to expand...

Hope you figured out how to open the files... other than the slightly embarrassing format and review isn't complete regarding units and values.

In regards to rectifier diodes... did wind up ordering some RGP10D... however, I'm thinking I could have went an improved more cost effective route with UF4003/4's.

In regards to capacitors... any reason why lower ESR in the audio frequency range Audio caps would be better in a power supply as I'd think those caps would be better in the audio circuit more? Not sure I understand off the top of my head the logic exactly as I think I can.
 

Attachments

  • RGP10A_to_M_Vishay_datasheet_fast_switching_suoer_diode_rectifier.pdf
    94.9 KB · Views: 5
  • UF4001_to_UF4007_Vishday_datasheet_UltraFast_Switching_Diode.pdf
    80.1 KB · Views: 1
Last edited:
Progress Report Update... received the electronics component orders.

Moving forward working my way in the power supply replacing what I find out of spec with a 91% IPA cleaning of the board after scraping old adhesive off where was found conducting.

Swapped out D58 with a 1N4003 for now, though old one measures OK out of circuit on the LCR meter.

Replaced C161 with a 50V 6800uF (old one measured like two diodes at first then a diode).

C162 was in spec out of circuit, so put back in for now.

Replaced C176 with a 50V 1000uF (old one measure 750uF 0.0ESR).

C177 was in spec out of circuit, so put back in for now.


Now at the D58 cathode-C176+ +22VDC and C177- -19.7VDC test points the relative values are +24.1VDC and -23.2VDC.

At the C161+ past the D57-D58 cathodes +38.5VDC and C162- D55-D56 anodes -38.5VDC test points on the schematic, I am getting the relative +40.5VDC and -40.5VDC.

See the attached image. Now to move in deeper and see what the observations are. :)

KR-720_Power_Supply_Region_Schematic_added_Info.jpg
 
Please note - the voltages you measured will vary with line voltage. For example, if a receiver is designed for 110 and you have 120 going in, all your unregulated voltages will be high by 9 percent. Or could go the other way.
I wouldn't be too concerned, as there should be tolerance of this in any decent design...
 
OK... probing around Q46 and Q45 I observed:

Q46 -2.8V value is -3.7VDC, 0V is 0V and the other lead is 40VDC .

Q45 37V value 39.7VDC before the 4.7ohm resistor.

Looks like the issue is further down the circuit. Time to read into the schematic some more and see what's next down the line.

KR-720_Power_Supply_Region_Schematic_added_Info2.jpg
 
NnionzngEMF said:
read into the schematic some more and see what's next down the line.
Click to expand...

Made some more measurements.

I also realized my AM antenna might not be tuned for AM so well and just tried a new antenna and along with the weak old LED TV 14watt speakers... I'm getting AM signals ok now. Same goes with improved FM. :music:

I did find however the what looks like 6 or 8V 70ma Lamp (can't tell... looks more like 8V) for the Tuner Indicator region light (illuminates tuner indicator moving vernier component) that looks like online are called "grain of wheat" lamps... is burned out.
KR-720_Tuner_Power_Indicator_Schematic.jpg
I found these posts regarding:
https://audiokarma.org/forums/index.php...
https://audiokarma.org/forums/index.php...
https://ogrforum.ogaugerr.com/.../led-headlight...

Wondering if this effects the Power Indicator strength LED's since I see leads going into the transistors related to the Power Indicator. Plus a Lamp acts like a resistor where an LED acts like a diode and resistor if I understand correctly.

Thinking I'll just use some salvaged components like a single TV LED since those are 6V and ~65mA with a current limiting resistor since looks like -19.7V goes into that. Maybe two 6V LED's since @ 12V will be dimmer only.

Wondering if there are any issues or concerns I need to consider, any experienced advice for this reborn electronics technician engineer wanna-be? :dunno:

Thanks
 
Last edited:
Semiconductor sources
220px-SiliconCroda.jpg

Silicon Se 14
 
avionic said:
Semiconductor sources
220px-SiliconCroda.jpg

Silicon Se 14
Click to expand...
I know... the resistor Lamp is probably better (tungsten, neon, Halogen, xenon, etc.?)... I'm sure I can make an equivalent and better than circuit with the items I have around (LED and resistors... maybe a capacitor to smooth ripple). I just need to review the math regarding worse case scenerio.
 
You must log in or register to reply here.
Back
Top Bottom