Farnell L30-5

[evansgo]

Hey all,

Just found you from a quick internet search, nice find

I have a Farnell L30/5 PSU, that I have had for over 30 years (eek) and this morning it decided to stop working I opened it up to take a look and saw the two fuse holders on the bottom that I never even knew existed checked them and all was sadly OK. Symptoms are that the main LED lights up, but no O/P.

Before I dig back into my memory to remember my electronics theory and investigate this in earnest, can anyone point me to any likely culprits? I did a quick check on the O/P transistors and they looked ok, although I've not unsoldered any yet to be absolutely sure.
Thanks

[MrBungle]

Worth checking the output switch. I've seen one where that was duff.

Also were you charging batteries with it? That seems to kill Farnell stuff.

[woodchips]

My one just stopped working, when checked all the components on the PCB seemed to have corroded so none were in fact soldered.

Not fixed, attempts to clean the legs of the Rs and Cs achieved nothing.

I had been using my one to charge sealed LA batteries, though not certain why that should have caused the problem, no reverse current.

[MrBungle]

If you are charging batteries there’s no reverse protection diode so when the DC source collapses during a mains transient or power failure it’ll blow the pass transistor and driver up. Very common problem with Farnell supplies. The two I’ve had go through had diodes added.

[duncanlowe]

Originally Posted by MrBungle

If you are charging batteries there’s no reverse protection diode so when the DC source collapses during a mains transient or power failure it’ll blow the pass transistor and driver up. Very common problem with Farnell supplies. The two I’ve had go through had diodes added.

I've seen it happen on another supply, Glassman 50A SMPSU. This one had an overvoltage protection circuit with a crowbar and was charging a large capacity car battery. All was well until someone knocked out the plug on the back for remote settings, and with this plug out the OVP trip was reduced to 0V and tripped. The crowbar device would have coped with discharging the supplies own caps and the current from the supply itself. It couldn't cope with trying to pull the voltage of the battery down and expired spectacularly. A diode was added in the leads after that.

[Diabolical Artificer]

Mine came with no OP. Easy things to check - after checking series pass Q's check sense resistor and swap opamp for any sort you have in your stash as long as it's pin compatable.

Andy.

[mhennessy]

Originally Posted by MrBungle

If you are charging batteries there’s no reverse protection diode so when the DC source collapses during a mains transient or power failure it’ll blow the pass transistor and driver up. Very common problem with Farnell supplies. The two I’ve had go through had diodes added.

With the E series, definitely. However, the L series includes these diodes...

When faulty, the E series give high output because the driver leaks heavily or goes short (never had an issue with pass transistors). However, this one is giving no output.

To the OP: what voltage checks have you done? The manual gives plenty of readings, so that's a good start. There are no "stock faults" as such - you're going to have to dive in. If you don't already have it, the manual is here: https://www.vintage-radio.net/forum/...08&postcount=2

Mark

[cmjones01]

I have an L30/5 which gets used from time to time, and it has a recurring problem with the contacts in the white Molex connectors on to the PCB. The usual symptom on mine is that the ammeter swings over hard right and the current limit LED comes on even though there's nothing connected. Removing and reseating the connectors usually fixes it until the next time I take it off the shelf!

Chris

[short wave]

info here (and circuit with voltages) the "l series" had 3 different control pcbs over its production run

https://www.vintage-radio.net/forum/...d.php?t=142722

regards S-W

[evansgo]

Originally Posted by mhennessy

With the E series, definitely. However, the L series includes these diodes...

When faulty, the E series give high output because the driver leaks heavily or goes short (never had an issue with pass transistors). However, this one is giving no output.

To the OP: what voltage checks have you done? The manual gives plenty of readings, so that's a good start. There are no "stock faults" as such - you're going to have to dive in. If you don't already have it, the manual is here: https://www.vintage-radio.net/forum/...08&postcount=2

Mark

Thanks all, I've done very little as I've been too busy at work at the moment, but I'll probably get stuck into it tomorrow.