Bench Power Supply (Identified as a Coutant).

[Radio Tech]

Hi folks

This is another project I have set out to complete I hope, trouble is I do not know the manufacturer of this power supply, all I do know is it has variable Voltage and Current controls, perhaps a 5V output and 0 to 15V and 0 to 10A marked on the meters, I have no idea of the circuit especially the small PCB which I think is the root of the trouble as there is no current or voltage output at the terminals. Does anyone recognise the PSU from the pictures and if so has anyone got a service manual / circuit diagram of this. There is 27V DC sitting across those huge capacitors rated at 9000uF 50V working.

Best wishes

Ken

[Herald1360]

Looks like a Coutant job.

Can you make out anything at the bottom of the stripe down the right of the front?

Edit: LB series? Perhaps from meter FSD something like LB1000-2?

Try here: https://www.vintage-radio.net/forum/...ad.php?t=93028

[Station X]

Looks similar to a Coutant I have. However mine has a single meter and a switch to set it to read V or A. You can also set a current limit.

[WME_bill]

Looks like a Coutant. I attach a picture,. I see I posted the full manual for the series L2A, LA2B, which go up to 15V 10A in January 2013, under thread Coutant LB1000-2. Have you searched.
The control circuitry is effectively the same for all versions, and just the number of pass transistors changed.
There is another version of LB2 which uses two SCR as part of the rectifier bridge. I attach the circuit of this as well to help identify which one you have. If this is your version, let me know.
Incidentally, I have a spare LB500-2, giving 30V5A, working well, as in the photo which I am selling.
wme_bill

[Refugee]

Cheers for the circuit diagrams. They will be helpful.
I have got a Belix one with pre-regulator to look at.
There is no chance of a circuit diagram.
The rest of the circuit is basically a DC coupled amplifier with loads of gain and negative feedback.

[threeseven]

That is a very sorry looking Coutant! Has obviously been stored in very damp conditions for some time. I'd check from the mains input forwards, there is a good chance the switch has suffered and is O/C or high resistance, or even the TX has died.

[Radio Tech]

Yes BIll, it is the same version as yours will PM you about the other one you have, and many thanks for the info, and oOK about the mains transformer Threeseven, it seems OK in this, and I agree it has been stored in damp conditions and suffered a bit but with a little TLC I think I can get it back into life. And thank you everyone else for their input.

Best wishes

Ken

[Radio Tech]

Hi Folks

Have checked some voltages between base and emitter on most of the transistors which read between 0.6 and 0.7V and all reference zener diodes seem to have their correct voltages but nothing on the output terminals. Any suggestions would be very much appreciated.

Ken

[threeseven]

I would check the voltage on the main power rail, across the reservoir cap. It that is present and correct at least you know the issue is in the control circuitry.

[Radio Tech]

Thanks threeseven, I am pretty sure the voltages across the reservoir capacitor are present and yes I think your right about an issue on the control PCB somewhere, I just wonder if there is some way of isolating the current and voltage sections so each can be checked through.

Ken

[threeseven]

Do you have the circuit description? Have you measured the auxiliary supply rail to the control board? It's supplied by a separate winding on the TX.

[Radio Tech]

Hi threeseven

I do have the circuit description and have measured the aux supply rail, they seem ok but I am a little confused over VT5 is it a pnp type or npn? the circuit isn't clear enough to define this and as Hammonds (Dave) listed VT5 as a BC107. I removed VT8 as this seemed to be getting too hot and the type that was on the board is a 2N2990 npn but I have only got a 2N3439 to replace it with.

Best wishes

Ken

[threeseven]

My circuit is also indistinct in the actual manual, but comparing the symbol with others it looks like NPN, so BC107 would be correct in that case. VT8 does run hot, hot enough for me to slip a small heatsink over it on other Coutant units I have of the same series, in fully working order!
Check the current sense resistor, R36, if that was o/c it would stop play.

[Radio Tech]

Thank you threeseven, I will check R36 and fit a heat sink on VT8, incidentally, I found VT1 to VT4 with BC557 transistor which are pnp types, on the circuit it states these as BC108 so I have fitted as per circuit. will update as I progress.

best wishes

Ken

[Radio Tech]

Hi folks

Thought everyone who contributed to this post would like to know the power supply is fully working. In VT5 I found a PNP type transistor now fitted with a BC108, there were in VT1 to VT4 PNP type transistors these change to BC108 types and a heat sink fitted to VT8, I might at some stage clean the front panel up but of course this will require the parts removed. Once again, thanks to those who helped and I will try and re draw the circuit diagram to make things a little clearer.

Best wishes

Ken

[threeseven]

Well done Ken! So, if I understand correctly, incorrect transistors were fitted in VT1 - 5?