For questions about troubleshooting circuits. Please note that repair questions must involve specific troubleshooting steps and demonstrate a good understanding of the underlying design of the device being repaired.

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0answers
58 views

Oscilloscopes - Comparing Traces

I'm new to Oscilloscopes and so this question may be a simple one. We have a Rigol DS1104Z Oscilloscope and would like to compare the same point in the circuit at different times as the voltage ...
0
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0answers
55 views

Why isn't my halogen floor lamp working with new bulb and new dimmer switch? [migrated]

I replaced the bulb and the dimmer switch. There is 120V between the connections when switched on. It varies between 115V on low and 122V on high. The bulb has continuity. I also measured the voltage ...
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1answer
65 views

What is causing a loud static POP when PTT mic is keyed?

Hi folks! I have been investigating this static POP noise problem for a while now, including talking to the sound shop I bought the amp from and consulting with the manufacturer of the amp. I am ...
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2answers
37 views

PCB outdoor moisture effect and protection

I have been working on a project that requires me to place a pcb outdoor for days to collect data. It has been done 3 times already, and all have failed with unknown reasons. First I thought my ...
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2answers
47 views

Soft-on/off circuit turns on on startup despite being jumpered to stay off, why?

So, I am building the soft-on/off circuit shown below and described here on a breadboard to test it out before I actually put it into a design. However, to better fit the parts on hand, I decided ...
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1answer
64 views

Will this phototransistor circuit work?

I'm building an 8 stage coil gun for a physics project, and I want to verify this circuit as I've never used a phototransistor before and I'm still pretty new to mosfets. Here is a schematic: The ...
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0answers
43 views

Voltage not correct for circuit

simulate this circuit – Schematic created using CircuitLab Left side of chip is all inputs. I have two of these circuits (IC9 and IC10) the IC10 circuit is working fine but this one i ...
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1answer
34 views

vibration activated delay ciruit

why this circuit doesn't work? I need this circuit to sense vibration, then after some delay, turn on the piezo beeper, and then after some delay, turn it off. Q1 is turned on when vibration is ...
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1answer
78 views

How can I troubleshoot stuck/flipped bits in a serial connection?

I'm working on reverse engineering some scrap vaccuum fluorescent displays from Noritake that lived their previous lives inside a payphone. No datasheet exists for it since it's a custom part; ...
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1answer
114 views

Strange output from an AD595 in single supply mode

device under test I've got a K-type thermocouple wired up through an AD595AQ to an Arduino in single-supply mode (12VDC to pin 11), with the addition of an RC filter across the thermocouple inputs ...
2
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1answer
168 views

Faulty relay(s), capacitor or power source? [closed]

I have this IKEA Bekant Sit/Stand electrical desk and all of the sudden today, it won't work properly. I push it to go up or down and it goes for a little bit and then stops. I can hear well the ...
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1answer
78 views

Troubleshooting 16x4 LCD Display Showing No Output

I have a 16x4 LCD (model DCM16433) that I suspect is dead. It has 14 pins rather than 16, but this should just mean no backlight. I have hooked pin 1 to Vss, pin 2 to +5 V, and pin 3 to a 10k pot, but ...
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1answer
57 views

Toubleshooting PCB circuit - strange Zener diode behaviour

I have two units of a device which I shall call deviceA and deviceB. DeviceB is malfunctioning. Therefore I compared the resistance values of the same components on the boards of both deviceA and ...
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4answers
117 views

Explantation for fried charger with Multimeter

I have a 9v AC to DC wall adapter that I use to power my Arduino boards. The label says it gives 9v at 1000ma but I wanted to test the validity of the label to troubleshoot. When I connected my ...
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2answers
1k views

transformer has continuity but no voltage output?

I have two old transformers that appear to be fine, however no DC voltage was measured on the secondary coil. I have measured: The input voltage: 229 AC the input coil ohms: 0.015 kOhms the two ...
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2answers
25 views

Troubleshooting stepper motor drivers

I repair intelligent lighting fixtures. These devices have a large number of motors, and so they also have a large number of motor drivers. It's not uncommon to have a single PCB with more than a ...
0
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1answer
53 views

Tracking a circuit path across a crack?

I am new to the world of electronic repair. I have connected several wires to this board and have been successful in getting the paths across the crack to connect. Is there an easy way to trace out ...
1
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1answer
118 views

Burning out relays when supposed to be within ratings

I am using this Normally Closed Relay on a 24V circuit: DataSheet The circuit is 24VDC source, which I measured the Amperage in series to be 29mA at the highest. I've breadboarded a lower voltage ...
0
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2answers
177 views

What is causing this step-up converter circuit to fail when introducing a transistor?

I built three separate circuits with the intention of making a colored led cycling solar sun jar. Each circuit works on its own. With just the RGB ATtiny85 circuit it works with 3x 1.2 volt AA NiMH ...
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1answer
110 views

Z80 control pins not reading a defined logic level

I'm having trouble getting my simple Z80 based project to work. I asked for help here last week, and received an excellent response on troubleshooting the Z80; here is the relevant part: There ...
2
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2answers
179 views

My Chua's Circuit is flatlining (i.e., malfunctioning)

I tried to build a Chua Circuit, but it doesn't appear to be working as expected. The problem is that, while it's supposed to be an oscillatory circuit, I see no oscillations. Refering to the diagram ...
0
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1answer
150 views

Z80 Simple Computer Troubleshooting: IORQ pin not going low

I'm following the instructions at http://www.reocities.com/SiliconValley/2072/z80proj1.htm to build a "proof of concept" Z80-based computer. I have wired everything on my breadboard, and programmed ...
3
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1answer
234 views

Crystal oscillator problem

Here is the datasheet of the crystal (32 MHz) that I use for a MCU. The right layout is an older version of my board which totally works fine. The left one is the newer version where I placed the ...
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5answers
120 views

A simple voltage divider

I attended a workshop on troubleshooting and we were asked to find the flaw in the given circuit. A guy pointed out to the organizer that R3 was short ckt and R2 was open ckt. However I was pretty ...
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1answer
377 views

PWM Red LED on Stellaris Launchpad

I am trying to PWM the red LED on a Stellaris LaunchPad, following the recipe in the datasheet p.706, taking a couple shortcuts from the Stellaris® Peripheral Driver Library. I cannot figure out why ...
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1answer
51 views

can an ammeter damage zeners

So I got this small circuit that plugs to the mains as power source. as for its DC converter, it's one of those transformer-less ones that drops the voltage with a resistors and filters before ...
0
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3answers
225 views

Tube Screamer PCB trouble shooting?

I recently bought a tubescreamer PCB from Tonelab and soldered it together yesterday. I decided to go for Ts-9 model which requires (Ra=470ohm, Rb = 100kohm, Ca = unused) I tried to match all parts as ...
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1answer
127 views

ATTiny85 wont turn on, not sure how to debug

The ATTiny85 in the below circuit refuses to do anything. ...
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1answer
344 views

GPIO using StellarisWare with LM4F120H5QR LaunchPad. SW2 not working as expected

I am trying to figure out how to properly use StellarisWare, the built in ROM calls, for GPIO. The Stellaris LaunchPad has two switches (SW1, SW2) and three LEDs (RED, GREEN, BLUE). I wrote a little ...
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1answer
195 views

undefined reference to `ROM_SysTickIntRegister'

I am trying to program the Stellaris LaunchPad to blink the red LED at 1 Hz, driven by the sysTick interrupt. I get an error though that I've been unable to solve yet. The C source I came up with ...
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1answer
137 views

Help Identify Faulty Component - Dishwasher Controller Board [closed]

Not sure if this is the right place to post this. Recently my dishwasher gave away :(. It works fine (goes through wash - rinse cycle)when empty but the moment it is loaded, the display lights go ...
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4answers
1k views

Can a current be induced in an HDMI cable that runs parallel to a 120v AC cable for 15 feet?

I just went to go unplug an HDMI cable and got shocked from the end of it! The only possible causes of this that I can think of are that the receiving or sending end of the long (50ft) HDMI cable is ...
5
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2answers
166 views

Ideas for troubleshooting a noise generator on a PCB

I am building an electronic "dice" that uses an ATTiny84 to sample avalanche noise from a 2N2222 in reverse-bias and generate random numbers, which are then displayed on 2 7-segment displays. When I ...
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3answers
1k views

Troubleshooting/debugging PCB

This may be an off topic question, but I'm sure many of you have the knowledge and experience to help out here. A quite complicated motherboard was flexed. The resulting symptoms include cross-talk ...
0
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1answer
217 views

Teensy 3.0 Problems with moderate range (~40m) OneWire Signals

I'm using a Teensy 3.0 (with its 3V TTL signaling) to try and communicate with some Dallas DS18B20 temperature probes. I'm not using parasitic power because I've heard a separate power line allows ...
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2answers
190 views

Multimeter question [closed]

I was trying to measure some voltage on cables going to ECU (car computer) and I had my multimeter in wrong configuration. It was set for 10 sec max 10A fused. When I touched the cables there was a ...
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2answers
170 views

Likely to fail components in amplifier board [closed]

I'm troubleshooting a car audio amplifier that has no life except for power led. I'd like to avoid having to pull it in a million pieces to find the broken component(s), so: What are the most likely ...
6
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2answers
2k views

My serial receiver verilog implementation does not act as expected

I have coded my own implementation of a serial receiver. It will work for incoming data at a baud rate of 115200. Here's my code: ...
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2answers
635 views

Why is my simple relay circuit only half working?

I am new to electronics and I am following the book "Make: Electronics" by Charles Platt. I have built a circuit with a 12V DC power supply, a 1K resistor, a relay, two LEDs, and a momentary-on ...
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2answers
1k views

Heating element as resistor for motor fan assembly in heat gun

Repairing the heat gun is not an option at this point, but out of curiosity I want to dig deeper into the problem: There are four wires associated with the heating element assembly, two of which ...
1
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2answers
194 views

Weird Behaviour with Bootstrapping Circuit

I'm trying to make a 3 phase BLDC driver and picked up some FAN7888s since they're inexpensive gate drives with all 3 phases on one chip. I read the relevant datasheets and application notes and ...
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0answers
502 views

L7805C/L7812C Voltage Regulator with 22V Solar Panel Not Outputting a Constant Voltage

First, here is my solar panel: http://www.amazon.com/Instapark%C2%AE-Black-Mono-crystalline-Charge-Controller/dp/B005LR9IOG And the regulator: ...
3
votes
2answers
275 views

Oscilloscope sweeps only once with DC sources and shows nothing on GND setting

I got an old CRT oscilloscope someone had laying around unused in his garage (an ATAIO AI 751A which seems pretty obscure, not getting any meaningful Google results). Unfortunately the user manual is ...
2
votes
2answers
694 views

Arduino: Only reads serial input when Serial Monitor is open. Fails when it's closed

I feel like maybe I'm having a brainfart, but I've been searching around a lot. Setup: I have a Python script using pySerial that connects to the device and writes a line to the serial port @ 4800. ...
6
votes
6answers
793 views

How do I find a short in an unpopulated 4-layer PCB?

I have a 4-layer PCB, designed in Eagle CAD 6.5. The stack-up is: Signal GND (ground) DVDD (digital power) Signal GND and DVDD are solid planes, with vias connecting them to layers 1 and 4. I ...
3
votes
1answer
782 views

ATtiny45 Timer1 clock misconfiguration

I am overlooking something with a very simple program for my ATtiny45. A program that divides the 16MHz system clock by 16 and outputs that on pin 5 (OC0A) using Timer0 and on pin 6 (OC1A) using ...
3
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0answers
99 views

Horrible noise after plugins power to my laptop plugged into effects chain [closed]

I'm using some stompbox effects with my guitar. I'm comparing them with my laptop where I have few VST effects. Everything sound clearly until I plugged power supply to the laptop. Then horrible noise ...
1
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1answer
262 views

Omron G5V-2 relay NO pins not working

I could swear that it was working for a while. I got back to my desk, tried it again, and it's no longer working. Could I have fried the NO pins on both sides? This is a DPDT relay. Everything works ...
5
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4answers
8k views

How do I check a BJT transistor if it is still functional?

Is there a simple method to do a sanity check on a bipolar junction transistor whether it is still functional or defective? simulate this circuit – Schematic created using CircuitLab Say ...
4
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1answer
1k views

Switching Boost Converter only works while probing with o'scope?

/See Edit below/: Why was the collector drive current not sufficient? I'm trying to improve a 4S LiPo (14.4V nominal) to 19V/3.5A boost converter based on the MC34063 PWM switch controller. I ...