1. How does it measure at its input pin I and its output O? Volts and Ohms in powered off state.
2. Where does it gets its power from?
3. What about the 120V input to the meter circuit!? Low ohmic?
If the circuits are separate the backlight of the meter should work isn’t it?
Post #1: “Elsewhere, this unit has six always-on receptacles that are powered, and four switched receptacles that are not. That issue looks unrelated to the voltmeter though, so that's one for another day”
Please re-evaluate that when checking out what the functionality of the device should be and how it is now. Possibly the errors are related. Since the answers appear a bit short/incomplete/uninterested/lazy (yup multiple choice 🙂) to me I wish you good luck with the repair.
Attachments
Last edited:
1. 0.74Vdc; 3.25 kΩ
2. I need to delve into that deeper, but at first blush it's coming from the circuitry that controls outlet switching / timing on the main board. And the switched / timed outlets are not currently working...
3. 210 Ω
OK, MFRD sent me a PM that he is not a lazy bum, he is just clumsy. Let’s solve this riddle.
First: there must be a pretty high current running somewhere that has PCB tracks melting/burning. Apparently there is not a fuse protecting catastrophe. That can be a too low ohmic value or short circuit.
So a solver wants to know where that current is flowing and why?
1. It has no voltage/is powered off. Why?
2. Measure that part of the circuit for low ohmic situations/short circuit. Maybe an onboard fuse blew and now some functionality is gone and no short appears anymore also possibly as the PCB tracks are now shot. The short circuit at the end should still be there normally. Pictures may help.
*just suppose things are interconnected (they are, the device runs on and switches 120V) and that circuit is a short circuit and has caused overcurrent. Now find it 😀
3. 210 Ohm on that pins or 210 Ohm at the point supplying 120V and the meter circuit disconnected?
Last edited:
MFRD, just a hint. You could reconnect the broken PCB tracks with crocodile clips and wires temporarily and NOT connect the device to mains but start measuring it for shorts.
Agreed! As you pointed out, an analog voltmeter in and of itself is unlikely to set stuff on fire, especially when it measures 70 Ω across so it's not shorted or anything. The PCB - well, nothing on it looks dodgy; there are no signs of overheating, no smells, all the components on it test OK. What's more, the 120 Vac path that feeds it is a straight shot from the main board's AC bus. No circuitry there between the AC bus and the PCB.
Which almost makes me wonder if those burned traces have anything to do with the voltmeter and its PCB? Someone has been in this unit before, trying to fix it - I assume to fix the 4 switched outlets that are dead. Could they have caused a short that blew the traces? I admit I would be more comfortable with this theory if there had only been one occurrence of burned traces - but they burned again after having been fixed once, so the person would have had to cause two shorts.
There is in fact no objective reason why the A-B circuit and the meter shouldn't work. I didn't want to power the unit with the meter connected because I was hesitant / afraid to feed 13.7V into a meter movement that overloaded on 1.5V.
Is my concern with powering the unit with the meter connected to the PCB misplaced?
The C-D circuit is another story. At 0.74V it's obviously not getting the voltage it should to power any kind of lamp, and I now believe you are correct when you suggest that the meter backlight problem may be related to the non-functioning switched outlets problem after all.
Since I am in 230V heaven I can only tell that 230V 16A home installations can make PCB tracks of a few millimeters (millifoot, micro thumb?!) width to powder/gas in milliseconds.
There are relays in that device, Chinese relays probably. Communist stuff! I would start there to check for shorts. No pics = no good hints. YOU are our eyes!
There are relays in that device, Chinese relays probably. Communist stuff! I would start there to check for shorts. No pics = no good hints. YOU are our eyes!
To clarify, I fixed the burned traces and powered up the unit. That was before starting this thread. I did not observe any issues. I scanned the components with my Fluke laser thermometer and temperatures were normal. I have turned it on a number of times since then and everything looks OK each time. What I have NOT done is power it up with the meter connected to the PCB. Hence my wondering about giving that a try.
You did not observe any issue except 4 outlets not functioning...
Anyway I suggest powering the meter circuit with meter safely outside of the device preferably with a TR5 fuse of any value till 5A in series with it. You'll likely see +/- 120V AC indicated.
Your problem is highly likely related to the non-functioning switched outputs. You buy me a beer when I am right OK?
Anyway I suggest powering the meter circuit with meter safely outside of the device preferably with a TR5 fuse of any value till 5A in series with it. You'll likely see +/- 120V AC indicated.
Your problem is highly likely related to the non-functioning switched outputs. You buy me a beer when I am right OK?
Last edited:
I connected the meter to the PCB, powered on the unit, and the meter works! Reading pretty much right on the money too, my house mains are 121.7V
Again, there were no signs of overheating while under power. Components read at or close to room temperature.
This supports the theory that the traces did not necessarily burn because of a fault in the meter or its circuitry, but because of some other factor that does not appear to be present at this moment but needs to be understood.
Other than that, issues left to solve:
The meter is not lit for at least 2 reasons:
@jean-paul is most likely correct that the insufficient voltage is related to the non-functioning outlets. I'll delve into that and post pics of the main board later.... If anyone had a line on some schematics, that would be super helpful!
Again, there were no signs of overheating while under power. Components read at or close to room temperature.
This supports the theory that the traces did not necessarily burn because of a fault in the meter or its circuitry, but because of some other factor that does not appear to be present at this moment but needs to be understood.
Other than that, issues left to solve:
- Four switched outlets are not working
- Meter backlight is not working
The meter is not lit for at least 2 reasons:
- No lamp (unless the dial itself is luminescent, which I doubt since the C-D pins read infinite resistance).
- Insufficient voltage (0.74V)
@jean-paul is most likely correct that the insufficient voltage is related to the non-functioning outlets. I'll delve into that and post pics of the main board later.... If anyone had a line on some schematics, that would be super helpful!
Another forum in the net has a post showing it to be axial 12V bulb allegedly dipped into blue paint by the device manufacturer.
https://forums.stevehoffman.tv/threads/replacement-light-bulb.900907/
But the backlight can (according to internet) also be turned off.
Does this device have a controller chip steering the receptacle relays and potentially the backlight?
I have been finding inadequate DC voltages all over the main board. There is one HA17339 IC that should get 12V and three relays with 12V coils that all get only 2.5V. The traces on the pic below marked "12V" and "GND" also read 2.5V across.
Bringing the DC voltage to spec will probably help with a lot of things. Also, the 2.5V is not stable; I've read as low as 1.9V and as high as 3.6V at different times.
The power supply consists of:
This is the point where I could use a little nudge in the right direction, guys... Does the low voltage mean the transistor(s) are bad, or could it be that the transistors are good but a faulty component or some other condition is causing them to misbehave?
The transistors can't be tested in the PCB, and I wish I could have a better understanding of the situation before I start de-soldering, testing, and re-soldering components (and risk damaging them in the process).
Here is the main board, top and bottom. Thanks in advance!
![main board [top].jpg](https://www.diyaudio.com/community/attachments/main-board-top-jpg.1339104/ "main board [top].jpg")
![main board [bottom]2.jpg](https://www.diyaudio.com/community/attachments/main-board-bottom-2-jpg.1339105/ "main board [bottom]2.jpg")
Bringing the DC voltage to spec will probably help with a lot of things. Also, the 2.5V is not stable; I've read as low as 1.9V and as high as 3.6V at different times.
The power supply consists of:
- Transformer with 120V primary and 12-0-12 secondaries (actual 12.75V)
- Center-tap rectifier with 2 diodes and a cap (reads 16.5Vdc across the cap)
- So far so good
- Next are two transistors (C945 and C1384) connected in a Darlington pair. And there is a problem, only 2.5V at the emitter of C1384 (which is essentially the emitter for the pair), instead of the 12V I'm pretty sure should be there. The pair of transistors is intended to control the amount of current that flows, and therefore the output voltage, correct?
This is the point where I could use a little nudge in the right direction, guys... Does the low voltage mean the transistor(s) are bad, or could it be that the transistors are good but a faulty component or some other condition is causing them to misbehave?
The transistors can't be tested in the PCB, and I wish I could have a better understanding of the situation before I start de-soldering, testing, and re-soldering components (and risk damaging them in the process).
Here is the main board, top and bottom. Thanks in advance!
Designed by Maradonna but chinese contract work as expected. Which are the wires/PCB tracks that burned? If it are short PCB tracks to the brown and black wire the suspicion is a short somewhere. Did you check the wires, their routing and their insulation? Do they measure continuity to either L, N or chassis (without the meter circuit connected)? Putting mains voltage on 2.54 mm pitched PCB connector pads is probably UL listed creepage/clearance blah blah but would not be seen as normal design practice here. The next PCB pad carries 12V DC....just 2.54 mm. There is not much needed for catastrophic failure so to speak.
Please check if the red and the orange wiring should have 12V so the regulator and backlight can be externally tested with 12V. It seems you mirror the pictures as I have a problem with the usual trouble free thinking in mirror.
Functionality of the device is severely hampered, one sees that assumptions that issues don't have anything to do with eachother don't lead to desired results.
Please check if the red and the orange wiring should have 12V so the regulator and backlight can be externally tested with 12V. It seems you mirror the pictures as I have a problem with the usual trouble free thinking in mirror.
Functionality of the device is severely hampered, one sees that assumptions that issues don't have anything to do with eachother don't lead to desired results.
Last edited: