# Thread: PET 4016 power in from transformer to Jumper 8

1. The schematic on Zimmers shows different pins on connector 8. I'm using the schematic that ( I think it was ) Dave_m posted.
It shows the center tap going to pin 4 and not pin 3.
See http://www.zimmers.net/anonftp/pub/c...8032087-11.gif
Note when we were talking about a floating center tap?
Dwight

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Originally Posted by daver2

Again, 18.4 Volts from 1-5 looks a little bit low?

Unfortunately, I had a tidy up over Christmas, and a key piece of paper (the transformer voltage readings from my system) have been stored away safely...

Dave
Thanks for your input on my dilemma!

1-3 =9.2, 3-5 = 9.2, 1-5 = 18.4.

3. >>> It shows the center tap going to pin 4 and not pin 3.

Which takes me back to my post #2 where something 'needled' me about pin 4...

I need to find my bit of paper that had all of this on...

I think pin s3 and pin 4 are swapped in some diagrams - either that or some PETs used pin 4 for the centre tap and others used pin 3...

>>> 1-3 =9.2, 3-5 = 9.2, 1-5 = 18.4.

So, you have Volts there - and both halves of the winding look OK.

Dave

4. I have just had a look at my PET.

The centre tap goes to pin 3 on J8.

Pin 4 on J8 has a red wire which goes to the capacitor positive terminal (as does J8 pin 2).

Pins 1 and 5 on J8 should have brown wires - these are the two ends of the double winding; and pin 3 of J8 should have a black wire - which is the centre tap.

J8 pin 4 is the positive output from the bridge rectifier 'going to' the capacitor which then 'comes back in' on J8 pin 2 to the +5V regulator.

It's getting a bit late in the UK, so I will measure my transformer voltages tomorrow - but Dave has posted his and your ac voltages look a little bit low when compared to his (18.4 Volts on yours and 22 Volts on his).

Dave

5. Originally Posted by Dwight Elvey
The schematic on Zimmers shows different pins on connector 8. I'm using the schematic that ( I think it was ) Dave_m posted.
It shows the center tap going to pin 4 and not pin 3.
See http://www.zimmers.net/anonftp/pub/c...8032087-11.gif
Note when we were talking about a floating center tap?
No, The center tap from the transformer is a black wire and goes to the negative terminal on the big C1 capacitor. From there, two black wires go to J8 pins 3 and 6. Both are grounded on the mainboard.

J8 pins 2 and 4 are red wires that go to the positive terminal of C1, The voltage there is the unregulated +9 VDC.

-Dave

6. Here is power supply circuit diagram.

PET PS copy.jpg

7. Hi Dave_m
Thanks for the clarification. The wiring makes sense now. I didn't look at the way they'd used the diode bridge.
Dwight

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xformersmall Webp.net-resizeimage.png

for reference, my readings (the image size restrictions on this forum are harsh).

so, where should i go next with this?

9. Please tell me you haven't got 17.2 Volts across J8 pins 2 and 6 though!!!

Ah, found my paperwork! I had put it somewhere safe after all!

I read approximately 8V AC from the centre tap (black wire) to each of the brown wires; and approximately 16.3V AC between the two brown wires. So I read less than yours (with no load).

It's all coming back to me now! J8 pin 4 is missing from the schematic in post #39 - which is why it is difficult to see how things work when you marry up the transformer/capacitor/J8 schematic with the main board regulator schematic. There is a wire missing from the schematic!

Dave
Last edited by daver2; February 20th, 2020 at 02:22 PM.

10. Connect things up again and remeasure. Make sure when doing DC measurements that the meter is set to DC.
Those reading that you have look correct.
Dwight

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