Time Electronics 609N

[mendip_discovery]

I have just had one come in for me to look at. Its got a burnt resistor. Dead battery. Plus a fuse that has lost its cap.

Anyone got one and is willing to open it up to get a resistor code for me? or a service manual?

[HighVoltage]

You should post some pictures of the unit and broken resistor.

[mendip_discovery]

Will do. I was at work so picture sending skills wasn't going to happen.

Is there a term for long term TEA sufferers who dislike other peoples test gear being binned just becuase it's old and no longer supported by the manufacturer.

[mendip_discovery]

The front of the unit.

The battery pack and charger. Some signs the battery is past its best.

One rather burnt resistor

This I suspect hasn't helped things, it was wedged in there but I fear its been wandering about for a while.

[mendip_discovery]

I found where its meant to go.

As I looked at this fuse the cap came off. I suspect its a F 250V 250mA fuse but a short dumpy thing at 15mm.

Most of the bits on this board look ok. But....

I fear that diode is past its best.

That would be another angle of the resistor.

The battery pack is made up of 11 cells, which I am going to guess were 1.5V so 16.5V. The battery is showing only a few mV so its dead. With it unplugged and running off the mains I am getting >22 V but with the battery in its getting some rather random number, 15 to 17V.

[George Edmonds]

Hi

This looks similar to the power supply for the later 2003N, I have a schematic for that power supply.

Don't waste your time asking Time Electronics, they will not help you in my experiance

G Edmonds

[BrokenYugo]

Battery is probably nicad, 1.2V nominal.

[George Edmonds]

Hi

Battery is made up of eleven NiCad's to be a nominal 15V.  Leaking electrolyte is normal after some time.

G Edmonds

[George Edmonds]

Hi

I have attached the drawings for the Time Electronics Ltd power supply.

The fuse is a 4.5mm X 15mm one. or 2AG type fuse  They were commonly known as a Belling Lee fuse and are available on that well known auction site.

There is currently a spare NiCad pack for sale on the same auction site, maybe search for 2003 battery pack.

I have been repairing and collecting kit for over sixty five years and continue to do so, it must be an addiction.

G Edmonds

[Dr. Frank]

Hello George,
do you also have the current source circuit to share with us, please?
Thank you.

I used these CC sources in 1989 at Aachen university, i.e. 10µA, 100µA or 1mA only for several kind of temperature sensors for low temperature experiments.
These Time Electronics sources were very expensive at that time, so I designed much cheaper fixed current sources with PWW resistors, FET and voltage reference, and calibrating them with the new 3458A. 

Frank

[HighVoltage]

I have a Time Electronics Model 1017 calibrator since 2015 but never opened it up.
Now for the first time.

It seems it still has the same PSU installed as yours.
Here are some pictures.

[HighVoltage]

And some more pictures

[tggzzz]

I have just had one come in for me to look at. Its got a burnt resistor. Dead battery. Plus a fuse that has lost its cap.

Anyone got one and is willing to open it up to get a resistor code for me? or a service manual?

No manual, but here are the equivalent photos from mine - without cells and without comment!

Marker pen "label" indicates cells were 13.2V 11*0.5Ah NiCd.

Fuse is 0.5/250V. External label indicates 1A.

[mendip_discovery]

Thanks for your replies. I have yet to get the go ahead to attempt the repair. I hope its just the battery unit (inc Resistor) and a fuse etc that needs fixing.

[tggzzz]

Thanks for your replies. I have yet to get the go ahead to attempt the repair. I hope its just the battery unit (inc Resistor) and a fuse etc that needs fixing.

That's easy enough to test. I operate mine from the mains without a battery; the voltage across the red/black leads is 17V with a 25mV ripple. I presume it would work with 11V (i.e. 1V/cell), but with a lower output compliance.

[mendip_discovery]

Some parts arrived and I brought the unit home to work on it in peace.

I tested the output voltage with no battery, 27V DC, measured the voltage from the transformer, 21V AC 50Hz. The back of the unit is marked up for 200/220 mains voltage.

The mains gets plumbed into a 6VA transformer, which happens to have 0 120 0 120 with the L and N connected to the first 0 and the last 120 on the transformer, the output has 0 7.5 0 7.5 and again that is connected to the first 0 and the last 7.5. Which to me seems connected up ok but odd that I am getting such high voltage out. But the 7818CSP Voltage Regulator is rated for 21-33V.

[George Edmonds]

Hi

If all is correct.

2 X 7.5VAC = 15VAC Multiply by 1.414 should give a maximum DC on C1 of 21.2VDC off load.

The schematic shows 2 X 12VAC windings in parallel.

I will open one of my PSU’s to check what is fitted.

On the face of it you have a faulty mains transformer, was this the original cause of the failure?

G Edmonds
 

[TaylorD93]

Check the Voltage at your mains inlet.

By your description, the transformer has 2x 120V windings in series, so equivalent to a 240VAC input, to 2x 7.5VAC secondary's in series.

A "standard" UK 230VAC supply can vary +10% -6%. So with a 253VAC input to a 240V transformer, your 7.5VAC (at full load) windings are now outputing 7.91VRMS, x2 (in series) 15.82VRMS, works out at 22.358Vpk.

If you are measuring 27VDC with no battery connected, there will be almost no load. 27VDC/22.358 = 1.207. (i.e. 20.7% load regulation)

A modern equiv Vigortronix 6VA 2x 7.5V transformer is quoted in its datasheet as having upto 24% load regulation.

So the math does add up. your measuring the output of the transformer likely after the bulk caps have charged and there is little to no load so the load regulation has increased, or that combined with a slightly higher line voltage. A variac would help clarify.

edit: so basically i suspect your transformer maybe fine.

[George Edmonds]

Hi

To provide a definitive answer, first if you want to take all the tolerances one way do not forget the 1.2V drop caused by the bridge rectifier.

I have two Time Electronics 2003 voltage standards which use the PU2 power supply as does the 509N.  When used in a 2003 the PU2 output fuse is 500ma and when used in a 509N it is 1A, this is the ONLY difference between the two uses.

I have previously provided the Time Electronics schematic for a PU2 supply, it clearly shows the secondary voltage of the mains transformer as 12VAC, both of my 2003’s have 6VA mains transformers with a 12VAC secondary output voltages.

It looks safe to assume that the correct mains transformer secondary voltage should be 12VAC NOT 2 X 7.5VAC in series giving 15VAC, has the mains transformer been replaced in the past with an incorrect one?

Off charge the NiCad pack gives exactly 14VDC,  with the mains supply in use the output of the PU2 is, as the test label indicates it should be, 16.4VDC.

A word of warning, be very careful when replacing the PU2 metal cover, it readily shorts out the power supply output.  Also keep in mind that switching the 509N off on the front panel leaves the mains applied to the PU2 supply.

G Edmonds

[mendip_discovery]

It has got me wondering what was the original fault. I will replace the resistor tonight and test again as that may be part of the switching circuit.

I will also attempt to measure the voltage coming off the regulator as that maybe the part that has failed.

For those wondering if it's my mains, I doubt it is the cause, I have good power stability here.

[George Edmonds]

Hi

I am sorry but I do not understand what is being said, “Switching circuit”?

This power supply consists of a simple transformer unregulated DC supply feeding a three terminal voltage regulator an MC78M18 the output of which goes via an isolation diode D3 to the output fuse, so when working you should never have more than a 17VDC output.

The unregulated DC is also used via TR1 to charge the NiCad pack.  A 741 is used as a control element for TR1.  It is possible without a battery pack fitted and a fault with TR1 or its control circuit for the unregulated DC supply to appear on the output fuse.

First you need to lift one end of D5 and check the output voltage at the fuse, this will check if the MC78M18 is working correctly.  I would suggest that say a 4K7 resistor is used as a power supply load for this test, checking the NiCad charging circuit is not quite so simple.

I also doubt that you have a mains voltage of 253VAC especially if you are not in a rural area.

G Edmonds

[mendip_discovery]

I noted a transistor on the board, guessed it was for switching of the charging current. Which with the battery disconnected and tested at the battery connection it's the same 27 volts dc.

I did try a diode test on a few that are on the board and they seem to be ok but I'm not that skilled at the repairs stuff yet.

[TaylorD93]

Sorry i meant check your voltage at your mains supply, i.e. 240V across the primary of the transformer, what is the actual figure?

[George Edmonds]

Hi

Under no circumstances should you have 27VDC on the output with a load on the supply.  There are three mechanisms by which you may have,

The MC78M18 has failed.
The leaking NiCad’s have caused the PCB to become conductive, needs cleaning anyway.
Shorted Diodes, mainly D3/D4 and D5

IC1 and TR1 along with the associated components form a charging circuit for the NiCad pack, it is both constant current visa R6 and D6 and has a cut off voltage controlled by the 741 with VR1 setting the cut off voltage.

Without a load on the power supply and a NiCad pack present R7 will up the output voltage above the designed 17VDC.

As to the failure mechanism, probably the 609N was left out of use for some time, at which point the NiCad’s became discharged and grew an internal short, this happens to NiCad’s.  When the 609N was next powered up the charging circuit was trying to work into a short and destroyed R6 and possibly other components.

Unless you understand the correct charging and behaviour of NiCad’s you will struggle with the repair and possibly setup the next early failure.  If I have to I will draw the current paths through this supply.

G Edmonds

[tggzzz]

With 10Mohm load and no internal NiCds, mine gives 15.6V on the output terminals.