Search found 59 matches

by MNTech
Wed Mar 20, 2019 6:20 pm
Forum: DSO138
Topic: No V- or AV- and U2 overheating
Replies: 1
Views: 2451

Re: No V- or AV- and U2 overheating

The schematic is on the last page of the assembly manual. The overheating of U2 and the short to ground on the output of U4 both say U2 is bad. A ChipQuik removal kit will help you safely remove ICs without damaging the PCB or the IC. video: https://www.youtube.com/watch?v=FTQqjggeklo Here is one pl...
by MNTech
Mon Mar 04, 2019 12:40 am
Forum: DSO Shell
Topic: C2 Capacitor value?
Replies: 2
Views: 2343

Re: C2 Capacitor value?

Here are two common ways capacitors values can be marked, EIA and ICE
In EIA 330 pF would be 331
In ICE 330 pF would be 330p

http://www.iequalscdvdt.com/Markings_and_Codes.html
by MNTech
Thu Apr 19, 2018 1:19 pm
Forum: DSO138
Topic: No Trace - High V2 Value
Replies: 1
Views: 2570

Re: No Trace - High V2 Value

Since the resistors values are correct there is little else to suspect besides the op amp. When the feedback on an op amp is working the plus and minus inputs will have the same voltage, zero in this case. Plus in is pin 10, minus in is pin 9 of U2. If the op amp is bad and outputting 3.44V pin 9 wi...
by MNTech
Fri Apr 13, 2018 4:21 am
Forum: DSO138
Topic: DSO138 troubleshooting - AV+ is negative (no trace)
Replies: 4
Views: 3803

Re: DSO138 troubleshooting - AV+ is negative (no trace)

You may have the same problem as in this post
https://www.jyetech.com/forum/viewtopic.php?f=18&t=1658

If not provide more details.
by MNTech
Wed Apr 11, 2018 12:17 pm
Forum: DSO138
Topic: DSO138 troubleshooting - AV+ is negative (no trace)
Replies: 4
Views: 3803

Re: DSO138 troubleshooting - AV+ is negative (no trace)

If the display works you have 3.3V and the 5 volts that feeds the 3.3V regulator.
The 5 volt supply is connected to +AV through L3.
Check L3 with your ohmmeter and resolder its connections.
by MNTech
Tue Apr 03, 2018 12:41 pm
Forum: DSO138
Topic: It works, but no trace
Replies: 2
Views: 3086

Re: It works, but no trace

With no input signal the voltage at test point V2 should be approximately 1.6V. I assume you have already done the Vpos Alignment. Do the Restore Factory Default procedure. Hold down [+] and [-] buttons simultaneously for 2 seconds. You will need to do the Vpos Alignment again after resetting the de...
by MNTech
Sun Mar 18, 2018 7:42 pm
Forum: DSO138
Topic: Trace line at the bottom of the screen, negative V2 voltage
Replies: 1
Views: 2527

Re: Trace line at the bottom of the screen, negative V2 volt

The voltage at V1 should be +1.6. The problem is at U2C or the surrounding components. Since V1 is 0 volts and is connected to U2 pin 10 you should have 0 volts there too. If the op amp is working U2 pin 9 will be driven to match pin 10. R10 and R11 try to pull pin 9 negative. The feedback through R...
by MNTech
Fri Mar 16, 2018 1:19 pm
Forum: DSO138
Topic: DSO-138 Calibration not possible
Replies: 2
Views: 4944

Re: DSO-138 Calibration not possible

The input of the scope uses basic resistor voltage dividers to set the range. However, like any real world, they are affected by stray capacitance. Extra capacitance is added in parallel to both the upper and lower resistors to compensate. The ratio of the impedances of the total value of stray and ...
by MNTech
Thu Mar 15, 2018 6:35 pm
Forum: DSO138
Topic: Faint/weak trace
Replies: 2
Views: 2511

Re: Faint/weak trace

Your resistance readings are consistent with a short to ground on the traces connected to V1 test point. I would first suspect a short at the switch. The trace to the switch passes under the corner of the metal frame of the switch. If the solder resist coating is damaged there that could be the site...
by MNTech
Sat Feb 10, 2018 11:21 pm
Forum: DSO138
Topic: Flat trace when calibrating probes
Replies: 14
Views: 8866

Re: Flat trace when calibrating probes

You can use power supplies with up to 12 volts output.