troubleshoot Phillips PE1509 power supply

[tonydix]

Ac volts from disconnected transformer 14.9 and 17
dc volts after rectification under load 21 and 25

I have made no change to the input voltage tap, we use an inverter to produce our mains voltage it about 112 volts. All the above have been checked with 2 meters and readings are close.

I did notice that s2 and s3 are connected so there is an ac voltage across both windings of 31 volts.

I am unclear about how you predict the voltages you suggest ie 25VAC or more across S2, and 21VAC or more across S3. Have you got access to data that I dont have ?

Many thanks

[pebe]

In answer to your last question. No, I don't know any more about the unit than is given in the manual and the circuit. I thought I had explained in earlier posts how I arrived at voltages required, but for the sake of continuity I'll repeat it here.

It is a 30V supply so the absolute minimum voltage required at TS29 emitter is 30V + the c-e drop of the TS29, So probably about 31V min allowing for some ripple on C30/C31.
The absolute minimum voltage on C26 must be (3 x 6.2) for the 3 zeners in series + 4.5V across R27 + about .5V (for TS26 with c-e saturated) = 23.6V. Those are the DC voltages.

Now for the AC voltage requirements. A rectified AC voltage from a bridge feeding into a reservoir capacitor with no load would theoretically charge it to the peak of the AC waveform (1.4 x its RMS value). In practice, the capacitor would draw heavy current from the AC when the diodes conduct during the peaks of the waveform, and so would 'flatten' them. So the peak rectified figure is nearer RMS x 1.25 or x 1.3. Then there is the voltage drop across 2 diodes in series of the bridge rectifier ( = 1.4V which I left out of my earlier calculations), so the formula simplifies to the minimum AC input voltage to rectifier = 1.4V + Peak voltage/1.4
In the two cases it would be:
For S2: 1.3V + 31/1.4 = 23.54VAC
For S3: 1.3V + 23.6/1.4 = 18.26VAC
And these needs are higher than the 17V and 14.9V voltages you read.
I hope that all makes sense.

So you run on an inverter. You have just added another unknown into the puzzle. So that I can get my head around all the possibilities, could you tell me:
1. Is the output waveform of your converter a square wave or a sine wave?
2. What voltage have you set the input taps for?
3. Is the converter the same one you were using when the power supply was working OK, or has it been changed?
4. Does your voltmeter calculate true RMS voltage (as distinct from one that derives a voltage from the average rectified DC level)?

[tonydix]

Thanks for your explanation. To answer your questions :-
1. Is the output waveform of your converter a square wave or a sine wave? sine wave
2. What voltage have you set the input taps for? 220 volts
3. Is the converter the same one you were using when the power supply was working OK, or has it been changed?. The inverter and the power supply on its present 220 volt setting was working perfectly. Nothing has changed but the PE1509
4. Does your voltmeter calculate true RMS voltage (as distinct from one that derives a voltage from the average rectified DC level)? neither voltmeter are true rms

Many thanks for all this help

[pebe]

If your mains supply is only 112V, why are you using the 220V tapping on the transformer?

[tonydix]

The unit is used in the UK and Panama to recharge drill batteries of 18 and 21,5 volts. It worked fine in both locations on the 220 volt setting. I will rewire for 110 volts (and try to remember to change when I go back to the UK) and let you know what happens. It used to work here on the 220 volt setting.
Thanks
Tony

[tonydix]

OK so here is the latest. Rewired for 120 volts. DC voltages increase to c30 60volts and c26 26 volts.
Unit operates partially ie connect a 12 volt light bulb as load we get a patially glowing bulb and 6 volts at the output. Increasing the voltage control (which is at about 15%) even up to max has no further effect.

So encouraged I reinstall bc179 and the unit stops working so we are back to the same problem as last sunday
Its a mystery !!
best wishes

Tony

[pebe]

It's looking better. How many supply volts to the TAA243? Should be very close to 18.6V.

[tonydix]

Only 17,5 volts on TAA243 AND with the 120 volt setting the chassis holding BDY20 gets uncomfortably hot while driving the 12 volt bulb as described previously (bc179 uninstalled). Perhaps a short ?

Thanks

Tony

[pebe]

17.5V for the TAA243 supply is too low. The three 6.2V zeners have insufficient voltage on them to conduct properly and that will upset the biasing of TS28 and TS30.

With a 26V supply across C26 there will be 5.1 V from TS26 base to +26V so there will be 4.4V across R27. That means it is passing a fixed current of 27.5mA, so TS26 acts as a constant current generator supplying 27.5mA. The TAA243 and the other transistors and resistors will take what current they need, and the remaining current will bleed off into the zeners to maintain 18.2V on TS26 collector.

To check that TS26 is working correctly, connect a milliameter (NOT a voltmeter) between TS26 collector and TAA243 pin4. It should read about 27.5mA. If it doesn't, then TS26, Z1 or R27 are faulty. If it does then more checks need to be done to find out where the problem lies.

Regarding the BDY20 getting hot, and the fact that you cannot get the voltage for it above 6V, it depends on the wattage of the bulb. You did not say what type it was, but if it is was car headlamp there is no way you can light it to full brilliance because it will take about 3A and your power supply just hasn't got that sort of power.

[tonydix]

Sorry if I am being dense :-
"connect a milliameter (NOT a voltmeter) between TS26 collector and TAA243 pin4"
Are we connecting directly as you suggest above,(and therefore possibly damaging something) or am I breaking a track somewhere to measure the current.
I am puzzled because ts26 collector is connected to pin 8 and ts26 base is connected via r26 to pin 4.
Perhaps I am getting too old for this !!
Thanks
Tony

[pebe]

I thought I had explained in the second para of my last post, how TS26 collector would supply a constant current of 27.5mA to its load - whether the load was the TAA243 supply or the zeners. The load could be anything from zero ohms to about 650ohms - any value in that range would have 27.5mA passing through it. If I didn't explain it well enough then I am sorry. But please take my word for it.

So if we want to know if TS26 is delivering that current then we can connect an ammeter in place of the load and measure the current. The 'current' ranges on a digital meter will measure the voltage across an internal shunt resistor and that will probably be 50-100mV. With only that low voltage available at TS26 collector (almost a short circuit), the zeners and the TAA243 would cut off, and the current through the resistor network to the right of the TAA243 would be negligible. So we don't need to disconnect those items to measure the current - it would all be going through the meter.

I hope that explains it.

[tonydix]

Thanks for your further explanation. The small 12 volt load bulb goes out and the meter shows 0.1 milliamps when the probes are connected so not passing 27ma.
I then checked r27 seemed fine but the byz88 zener did not. It passes a small current in both directions. I will have to seek out a replacement which may take a few days. Thanks for your help, it is much appreciated. Tony