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Search: Posts Made By: redwire
Forum: Equipment Usage, Soldering, Techniques, and Reviews Yesterday, 07:51 PM
Replies: 150
Views: 18,605
Posted By redwire
Re: New tool to find short capacitors on motherboards : shorty with display

I'm wrong about some of the test currents. I checked math again and the circuit with 5V is putting a max of around 58mA through the resistor under test, with 114mV open-circuit. So this looks quite...
Forum: Troubleshooting Game Consoles & Other Weird Devices Yesterday, 12:30 PM
Replies: 3
Views: 77
Posted By redwire
Re: Chinese no brand ultrasonic cleaner

I would check resistance across the electrodes and between each to the metal chassis, to ensure the transducers have not shorted or have a ground fault. You can also measure their capacitance for...
Forum: Equipment Usage, Soldering, Techniques, and Reviews Yesterday, 11:56 AM
Replies: 150
Views: 18,605
Posted By redwire
Re: New tool to find short capacitors on motherboards : shorty with display

I think the original circuit does not push much current through the probes?
BC557 switching around 56mA but most of that goes through R2 2Ω which is in parallel with the tested resistance, and by...
Forum: Troubleshooting Game Consoles & Other Weird Devices 07-01-2022, 01:14 PM
Replies: 6
Views: 91
Posted By redwire
Re: Digital desk clock runs fast

Ahh much better pics :) But this is mains powered? I would check the electrolytic capacitors, I have seen alarm clocks run fast counting extra pulses due to noisy DC power from old caps.
The other...
Forum: Troubleshooting Game Consoles & Other Weird Devices 07-01-2022, 10:46 AM
Replies: 6
Views: 91
Posted By redwire
Re: Digital desk clock runs fast

I can't see much pics are thumbnails?
I find the crystal tuning is done wrong and they run fast, these 3V clocks. The loading caps are important and how fast they run changes with battery voltage...
Forum: Equipment Usage, Soldering, Techniques, and Reviews 06-30-2022, 03:37 PM
Replies: 150
Views: 18,605
Posted By redwire
Re: New tool to find short capacitors on motherboards : shorty with display

A one or two transistor constant-current source is not difficult, and possible to voltage-limit it. On laptops, GPU etc. I could see a need to keep it under 2V max.
Forum: General Capacitor Questions & Issues 06-30-2022, 03:31 PM
Replies: 9
Views: 179
Posted By redwire
Re: 3300F 450V caps...

In the repair shop one tech would charge caps to 400VDC in the Heathkit and toss them at you yelling "catch!". I let them fall on the ground but a few people got nailed.
Forum: General Electronics Technical Discussion 06-30-2022, 03:29 PM
Replies: 30
Views: 260
Posted By redwire
Re: flourescent ballast resistance

I know two-wire tubes are cold-cathode. If you have a HV AC source, like a car ignition coil+555, you can put the HV wire anywhere near the tube and it will ionize and light. BBQ lighter not sure....
Forum: General Electronics Technical Discussion 06-29-2022, 01:32 PM
Replies: 30
Views: 260
Posted By redwire
Re: flourescent ballast resistance

Pic shows two wires to the tube and the Osram datasheet (https://www.osram.com/appsj/pdc/pdf.do?cid=GPS01_1027844&vid=PP_EUROPE_Europe_eCat&lid=EN&mpid=ZMP_58994) showed two and said DULUX S is CFL....
Forum: General Capacitor Questions & Issues 06-29-2022, 12:19 PM
Replies: 9
Views: 179
Posted By redwire
Re: 3300F 450V caps...

You can do the math but the energy to lift up a person a foot off the ground, is stored in one cap. How far a commie would launch... they're full of so much hot air lol.

I don't short...
Forum: General Electronics Technical Discussion 06-29-2022, 11:15 AM
Replies: 30
Views: 260
Posted By redwire
Re: flourescent ballast resistance

Oh it's cold cathode? Then it's just a matter of the starter/ballast making a kV pulse. Sometimes holding the tube or having it next to grounded sheet metal helps it ionize at lower voltages.
There...
Forum: General Electronics Technical Discussion 06-28-2022, 03:28 PM
Replies: 30
Views: 260
Posted By redwire
Re: flourescent ballast resistance

That seems reasonable. You can check if there is a ground fault, winding shorted to case.
If the overall startup current is too low I think the starter will just sit there trying to get the...
Forum: General Electronics Technical Discussion 06-28-2022, 02:10 PM
Replies: 30
Views: 260
Posted By redwire
Re: flourescent ballast resistance

I would measure its inductance. F14T5 is 14W 0.265A lamp current, need around 900ohms impedance, so 148R from the coil and maybe ~2.5H is needed. Using 240VAC and 40V tube drop for rough math.
Does...
Forum: Troubleshooting Game Consoles & Other Weird Devices 06-28-2022, 10:46 AM
Replies: 17
Views: 268
Posted By redwire
Re: Graco ST MAX II 495 PC PRO , paint spray machine help

I understand the conformal coating can make the repair extra hell. I use needle probes to poke through for readings, and hot air gun to heat/soften the coating and scrape it off.
TBH the board is a...
Forum: General Electronics Technical Discussion 06-28-2022, 10:42 AM
Replies: 18
Views: 244
Posted By redwire
Re: Reading input and output of bridge rectifier on the same scope?

OP it's always good to have a fuse/1A circuit breaker because transformers can put out much more current into a short circuit.
Check the scope's internal ground did not melt open, I have seen that....
Forum: Equipment Usage, Soldering, Techniques, and Reviews 06-27-2022, 11:11 PM
Replies: 12
Views: 395
Posted By redwire
Re: Short finder

All that is missing is a PCB layout? It's not that complicated, it's just people wanting changes and complaining etc. that takes away all the fun....
Forum: General Electronics Technical Discussion 06-27-2022, 05:56 PM
Replies: 4
Views: 131
Posted By redwire
Re: Microwave advise please

Last to check is for open filament wiring at the connector/feed-through capacitors or for a bad connection there, or inside the can at the EMI chokes. Magnetron filament is low voltage, high current...
Forum: General Electronics Technical Discussion 06-27-2022, 04:06 AM
Replies: 52
Views: 2,711
Posted By redwire
Re: Fixing a multimeter based on VC9805 schematic

Display shows 1___ with those readings?
Pin 40 COM voltage is too low, it needs to be at least 1V above V-. On the schematic it would be QC4,QC3 to check- that would short COM below 1V. On your...
Forum: General Electronics Technical Discussion 06-26-2022, 11:20 AM
Replies: 18
Views: 244
Posted By redwire
Re: Reading input and output of bridge rectifier on the same scope?

Fixed: just as well oscilloscopes are sold in packs of 10 on aliexpress! :D
Forum: Equipment Usage, Soldering, Techniques, and Reviews 06-26-2022, 11:17 AM
Replies: 9
Views: 196
Posted By redwire
Re: Buy a Agilent U1242A or Fluke 179 DMM?

I'm repairing three old American-made multimeters, but I might have maxxed out at having 10 lol I've got no Flukes, just HP, Beckman, Wavetek.
I hate Taiwan-built multimeters, either they blow up...
Forum: General Electronics Technical Discussion 06-25-2022, 02:11 PM
Replies: 11
Views: 192
Posted By redwire
Re: Conversion of Anolog Voltmeter into Ammeter

"the meter still needs to be touched to work".
Find the bad connection, then worry about the design issues.
Forum: General Electronics Technical Discussion 06-25-2022, 10:29 AM
Replies: 11
Views: 192
Posted By redwire
Re: Conversion of Anolog Voltmeter into Ammeter

Your test setup looks good, I think there is a poor connection or maybe a switch is inside the meter so you must press it down to take a reading.
Usually panel meter specs are two things - the coil...
Forum: General Electronics Technical Discussion 06-24-2022, 09:54 PM
Replies: 52
Views: 2,711
Posted By redwire
Re: Fixing a multimeter based on VC9805 schematic

Post #28 I said to use a multimeter and measure some voltages "On DCV 20V range, measure the A/D voltages: IN HI, IN LO, REF HI+, REF LO-, COM wrt V-"
That is 5 readings to take.
Forum: Troubleshooting Game Consoles & Other Weird Devices 06-24-2022, 09:51 PM
Replies: 7
Views: 152
Posted By redwire
Re: Turbo Start QPET 16V/25A racing charger repair

It looks like a typical battery charger using phase control. The SCR's gate is driven by the H11 opto-couplers U4, U5. There's a current-transformer so it must do CV/CC control.
The only scenario...
Forum: General Electronics Technical Discussion 06-24-2022, 12:41 PM
Replies: 18
Views: 828
Posted By redwire
Re: Using car key fob as generic remote control

Check the RXB6 pinout, it has an enable pin 6 which floats high to enable data, not power save.
Some of those 433MHz RX modules have extremely weak data output 10uA (!) so a low value pullup or LED...
Showing results 1 to 25 of 500

 
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