Altronics Dual Rail power supply - troubleshoot

[Tarvis]

Hi folks,

I am relatively new to electronics and have just finished building the Altronics 19v dual tracking power supply kit. Its been challenging at times but i've worked slowly and carefully through it.

I've gone to boot it up for the first time last night and to test it according to the instructions. The V+ channel seems fine but i am unable to adjust the voltage on V- using the potentiometers. I am also unable to adjust the voltage via the variable resistor that is part of the calibration stage - the displayed voltage just doesn't move.

I guess i am really just looking for pointers on how I would go about diagnosing the source of the problem. I'm sure it could be 100 things, but given this unit has mains voltage in it I am a little wary, and want a bit of a plan to problem solve.

Thanks in advance. Pls reach out if you have other questions.

Trav

[floobydust]

Welcome to the forums    It's an ambitious project for a first go, but something we can help you sort out.

The original project I think is from Silicon Chip Magazine, Dual Tracking Power Supply, June&July 2010. I don't have access to it, it's behind their paywall. I found this schematic and repost it here. Is it what you have?

Repairing/troubleshooting electronics, the first thing you do is use your eyes. Look around for poor soldering, wiring mistakes, missing parts, burnt parts etc.
Because you are having problems with the -ve output, I would look there first. Is the transformer secondary is connected right (not mixed up center tap), jumper LK1 is out, rectifier diodes D1-D4 are in right and test OK. NO electrolytic capacitors or IC's in backwards 
Double check the resistors are the right value (you can use a multimeter if the colour codes are hard to read). In-circuit some places you cannot read a resistor's value due to nearby connected parts, and one leg needs to be lifted up.

Second thing when repairing/troubleshooting electronics, is to check the power supply (internal) voltages are present and OK.  Do you have the + and - 15V rails up from REG3 and REG4. The + and - 1.3VDC rails are working? The panel meter is a separate issue I would leave until later unless it's wired wrong and shorting the -V output ore something.
If you are worried about taking measurements while it's powered up, you can put black electrician's tape over the exposed mains connections. An isolation transformer is ideal but you might not have one. I go in just extra careful, that I am not touching grounded metal, use one hand, or cover the mains connections with a piece of wood or something so it's not so scary. I connect my multimeter (-) to the output common and then just move one probe and poke around, it's easier than two hands and two probes. Write down what you get for readings.

I'm not sure what Altronics K3218 gives for assembly instructions etc. or it's just the PC boards. There was an errata, not sure if it's fixed for your build.

Code: [Select]

Errata Dual Tracking Power Supply, June-July 2010:
(1) The labels for V± and Ilim were swapped on the front panel artwork. Updated front panel artwork has been provided to the kit suppliers and is now available on the SILICON CHIP website. In addition, some constructors have found that VR7 has insufficient range to properly trim the V± reading. In this case, increase the value of its 68 ohms shunt resistor or remove the shunt resistor entirely. (08/10)

(2) There are two errors in the circuit diagram of Fig.2 in the June issue. The 820 ohms resistor connected to pin 1 of IC4a should be 68 ohms while the 100k resistor from Vout- to the top of VR7 should be 10k. The layout diagram (Fig.8) in the July 2010 issue is correct. In addition, the wiring diagram (Fig.11) shows the top and bottom connections to the VOLT ADJ header (CON6) transposed. Also, the leads to pins 5 & 6 on the panel meter must be transposed for the Altronics display. (09/10)

(3) Under some conditions, if the supply is switched off then on again soon after, the negative output current sense display may not operate correctly. To solve this, a 1N4148 or 1N4004 diode can be soldered between the output of IC2a and ground, with the anode to ground. This can either be soldered to the underside of the main PC board or to the electrically connected pads on the rear of the front panel board. (01/11)

(4) The circuit diagram on pages 70-71 of the June 2010 issue shows the wiper of VR2 connected to one end of the track when it should not be. The circuit board and overlays are correct. In addition, the two wires from the “LED PWR” connector on the main board to the front panel board should be swapped on the wiring diagram on page 84, July 2010.

Finally, the wiring for the Jaycar LED panel meter shown is correct according to the manufacturer’s data sheet but we have found that the connections to its pin 7 & 8 (or pins 5 & 6 on the front panel board) must be swapped for it to work correctly. In practice, this simply involves swapping the yellow and red wires to the display connector. (08/11)"

[Tarvis]

Thanks Floobydust,

That is the schematic and project I'm talking about.

I've booted it up again this morning and for clarification, i think I have no voltage at V- rather than just being unable to vary it. The panel meter is reading 0.25v but I'm wondering if this is just calibration and its actually zero. A multimeter shows almost no voltage present at V-.

My kit is relatively new so I don't think would have those issues you mention below in the errata, but I'll check regardless.

Thanks for the tips below, I will work through this list. Power looks to be wired up correctly. I've checked the electrolytics, I'll move on to the diodes next.

[CJay]

The first thing I would do would be to very carefully inspect the soldering again, then print out a copy of the parts list and PCB layout, cross check the parts values on your board against both and tick them off on the printouts.

Even now with a few decades of experience, I still occasionally make mistakes, it happens.

Once I'd done that if I hadn't found a problem I'd start digging out the multimeter and checking supply voltages to chips.

[timenutgoblin]

Check the wiring of the 'METER FUNCTION' switch S1 against the schematic. Start at the Digital Panel Meter and check DPC, DP1, DP2 and DP3 going to S1b. S1a is wired differently.

DPC is connected to the common terminal on the switch S1b.

DP1 is connected to the following:

I_LIM, -I_O and +I_O are connected together at the switch.

DP2 is connected to the following:

-V_O and +V_O are connected together at the switch.

DP3 is connected to the following:

+/-V_O is independent on the switch.


Fortunately, you have access to a schematic. Also, there is a discussion thread relating to this PSU:

https://www.eevblog.com/forum/beginners/adding-digital-control-to-dual-tracking-lm317-lm337-bench-supply/

[Soundev]

Have also had difficulty with this kit and many of the assembly instructions are not clear.
It is possible you have a short from the regulator mounting tabs to the heatsink like I had
The mounting holes in the rear panel are too small to fit the insulation bush.
Drill out from 3mm to 3.5mm.
Re meter issues have solved this problem.
How are you connecting the main board to the front panel board?
Are you using header sockets at both ends of the ribbon cable or header socket and solder connections?
Let me know
Thanks Ross