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Search: Posts Made By: redwire
Forum: Troubleshooting Power Supplies and Power Supply Design Today, 12:32 PM
Replies: 15
Views: 46
Posted By redwire
Re: Voltage Regulators and Heat Issues

Your piezo drive circuit sucks, you need a resistor across it to discharge its capacitance and bring the crystal back. AC drive is best.

With an added inductor, you can get over 5-10X the voltage...
Forum: Troubleshooting Power Supplies and Power Supply Design Today, 11:16 AM
Replies: 15
Views: 46
Posted By redwire
Re: Voltage Regulators and Heat Issues

It is common to add an inductor to make a boost converter just for the piezo buzzer. This can make is very loud. It is used in some smoke alarms and battery powered things where you want more than 3V...
Forum: General Electronics Technical Discussion 03-18-2019, 07:17 PM
Replies: 9
Views: 144
Posted By redwire
Re: Failed RF power transistors...DC testing (i.e. with multimeter)?

Depending on the frequency, hams are converting some transmitters from BJT to mosfet. It's also a popular mod for CB radios.

For your TX, the problem might be upstream at the driver stage, or bias...
Forum: General Electronics Technical Discussion 03-16-2019, 01:17 PM
Replies: 9
Views: 144
Posted By redwire
Re: Failed RF power transistors...DC testing (i.e. with multimeter)?

In-circuit testing rarely works because there are shunt inductors or transformers in tuned circuits, so you get low ohms across the diode-junctions.

Newer RF PA parts are mosfets, BJT's with Si-Ge...
Forum: Troubleshooting Power Supplies and Power Supply Design 03-14-2019, 09:29 PM
Replies: 14
Views: 870
Posted By redwire
Re: Recapping Tektronix 2235 PSU

For C956:
2235A has a pi-filter with C956 10uF and Tek added C957 270uF, for the +30V rail. So there are two capacitors.
2235 has no pi-filter or C957, so only C956 270uF.

To replace C906, put...
Forum: Troubleshooting Power Supplies and Power Supply Design 03-14-2019, 08:51 PM
Replies: 25
Views: 312
Posted By redwire
Re: Apple ][+ Astec power supply

Apple II power supply Astec AA11040 or AA11040-B schematic etc. https://ia801002.us.archive.org/1/items/Astec_Power_Supplies_Aug82/Astec_Power_Supplies_Aug82.pdf
Have to look inside to see what part...
Forum: General Capacitor Questions & Issues 03-13-2019, 01:47 PM
Replies: 5
Views: 2,807
Posted By redwire
Re: Wurth capacitors

Wurth trying to bust into the capacitor business, they have great pricing and the film caps are good.
Wurth electrolytics are made in china and seem like a cheap build (low hrs lifetime) despite the...
Forum: General Electronics Technical Discussion 03-10-2019, 03:07 PM
Replies: 15
Views: 210
Posted By redwire
Re: Dead car battery and alternator strain?

Older (car) generators and dynamos needed output current limiting so they would not burn up under heavy load. This was done by a current-sense winding on the relay coil in the mechanical regulator,...
Forum: General Electronics Technical Discussion 03-08-2019, 02:34 PM
Replies: 15
Views: 210
Posted By redwire
Re: Dead car battery and alternator strain?

I see temperature has a big effect on lifetime.

Johnson Controls revenues $6 billion for car batteries, 135 million made per year. They are pretty much the big dog making almost all car batteries,...
Forum: General Electronics Technical Discussion 03-07-2019, 07:53 PM
Replies: 15
Views: 210
Posted By redwire
Re: Dead car battery and alternator strain?

Modern cars have high drain with the key off. 50-100mA so battery life is short, it's always discharging.

Car battery main failure is usually corrosion of the plates. What do you expect to happen...
Forum: General Electronics Technical Discussion 03-07-2019, 11:39 AM
Replies: 4
Views: 114
Posted By redwire
Re: Help identify component?

The Toshiba U5ZA27 zener is in a Toshiba-exclusive package, slightly different size than the Vishay part and rated 1/2 the max. current. I'd stuff the Vishay part in lol.

It's neary impossible to...
Forum: General Electronics Technical Discussion 03-07-2019, 11:28 AM
Replies: 15
Views: 210
Posted By redwire
Re: Dead car battery and alternator strain?

You can't charge a block of ice - so if the battery went dead and froze, you'll probably have to bring it inside and thaw it out to charge it.
It depends on how cold and how low the battery is....
Forum: General Electronics Technical Discussion 03-06-2019, 12:52 PM
Replies: 4
Views: 114
Posted By redwire
Re: Help identify component?

That looks like a massive 6,600W TVS DO-218 used in automotive electronics. It can withstand load dump and surges.
I know it as Vishay SM8A27 (https://www.vishay.com/docs/88386/sm8a27.pdf) used on...
Forum: General Electronics Technical Discussion 02-27-2019, 12:29 PM
Replies: 22
Views: 304
Posted By redwire
Re: The extrasensory perception solder iron.

I hate (Hakko) brass wool, I find it's hard on tips scratches the plating. Damp sponges have always worked fine. Not making a steam bath like some dumb people seem to enjoy.
If there is black slag...
Forum: Troubleshooting Power Supplies and Power Supply Design 02-27-2019, 12:23 PM
Replies: 62
Views: 9,730
Posted By redwire
Re: Muskoka 35" curved fireplace power supply.

Yes the AC Line "L INPUT" comes into the board through the big relay top spade terminal. Then you need Neutral to pin 1 of the other connector, to give the board power.

I would check the "fuse"...
Forum: General Electronics Technical Discussion 02-20-2019, 08:33 PM
Replies: 20
Views: 353
Posted By redwire
Re: Microwave Issue

I would say that's not right because the circuit is a half-wave voltage doubler and it does not output pure DC.

If you use a scope and HV probe, you will see 1/2 wave pulsating DC from +11V to...
Forum: Equipment Usage, Soldering, Techniques, and Reviews 02-19-2019, 03:06 PM
Replies: 22
Views: 314
Posted By redwire
Re: Is this really LMP silver solder?

I've used it to solder to stainless steel
Forum: General Electronics Technical Discussion 02-19-2019, 03:05 PM
Replies: 8
Views: 142
Posted By redwire
Re: Repair LCD display contact rubber!

They are made of alternating (zebra stripe) layers of silicone rubber. The conductive black stripes are carbon-filled silicone rubber. The support portion is usually (pink) sponge rubber or (greyish...
Forum: General Electronics Technical Discussion 02-19-2019, 12:21 PM
Replies: 8
Views: 142
Posted By redwire
Re: Repair LCD display contact rubber!

I soak zebra strips in hot water and stretch them a little bit by hand.
This seems to make them bigger, like they were before the LCD compressed them.
Forum: General Electronics Technical Discussion 02-16-2019, 05:31 PM
Replies: 20
Views: 353
Posted By redwire
Re: Microwave Issue

+1

The majority of magnetrons are 3.3VAC >10A filaments, so with the transformer disconnected expect under 0.33 ohms.
I would check continuity from filament to housing and tap it, bang it a bit....
Forum: General Electronics Technical Discussion 02-16-2019, 02:13 PM
Replies: 20
Views: 353
Posted By redwire
Re: Microwave Issue

Can you give us a make and model number, that helps for the schematic.
Some microwave ovens use both a rectifier and a protection (across capacitor) diode.

If the new HV fuse is not blowing, then...
Forum: General Capacitor Questions & Issues 02-15-2019, 10:39 PM
Replies: 4
Views: 189
Posted By redwire
Re: Nichicon radials without the X vent?

I have some UPW1E100MDD6 from Digikey. (https://www.digikey.com/product-detail/en/nichicon/UPW1E100MDD6/493-1810-ND/589551) No X vent, and no flat bung, and N621 text as well. The white printing is...
Forum: General Electronics Technical Discussion 02-13-2019, 08:24 PM
Replies: 20
Views: 229
Posted By redwire
Re: Measuring crystal oscillators with scope ?

Ceramic resonators are lower cost and tougher than quartz crystals, but not as accurate on frequency. The 3-pin parts have built-in loading capacitors.

A scope probe has capacitance and loads down...
Forum: General Computer Discussion 02-12-2019, 06:16 PM
Replies: 14
Views: 244
Posted By redwire
Re: "Save Image As" I always get a 25KB .jpg that is HTML

It happens on other websites, "Save Image As" generates an image filename .jpg or .png - but the file is not an image file, it is HTML.

Unable to upload two image saves from Badcaps threads as...
Forum: General Electronics Technical Discussion 02-11-2019, 06:15 PM
Replies: 58
Views: 530
Posted By redwire
Re: Car LED Headlights dimmer?

You can lower the buck-converter output current by removing one or two of the three sense resistors R2, R3, R4 that are 0.25R each.
If the 6-pin IC is QX9920, roughly... all three = 3A, two = 2A,...
Showing results 1 to 25 of 500

 
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