G7 PSU Help Needed

Hello,

now I just finished building my G7 mic and the psu, unfortunately they don´t work yet ;-((
I suspect the psu because I could not measure any 9VAC or 6V DC for the heater, nor the 120 VAC. I measured the Voltage where it goes to the pcb from the transformers, being a newbie, I put one wire from the Multimeter to one of the 9VAC solderpoints, the other one to the chassis, I hope I measured that right? I guess I should get 9VAC from each of those points? And 120 VAC from each of the other 2 points?

So I think I made a mistake wiring the connections of the 2 transformers, I tried all different combinations, but could not get it to work (I am using two of those blue print transformers, I hope I got the right ones?).

I made a little picture, looking at them from the top, I´m sure any of you experts could tell me the right way to connect them.

http://www.3dmedicalanimation.com/downloads/TransformerG7_Psu.jpg


thanks for any newbie help,
reggie

please, can anyone help?

I tried countless variations how to hook up those 2 transformers, but it never works. Sometimes I can measure 10 V on either 1 or 3 of the pins, I never got 160 VAC anywhere. Could I possibly have destroyed them?

thanks for any clues,
reggie

You should not measure from chassis to the transformer AC, as there is a bridge rectifier between these points.

Measure across the transformer in stead.

Jakob E.

thanks for the info!

could it be, that I bought the wrong transformer for the first one, it has only ONE secondary of 9V (although there are 4 pins, maybe that´s where I went wrong in the first place and 2 sec are needed)?

reggie

Make sure you check the specification sheet on your transformer. Four pins probably means two sections.

I checked the transformer but there is definetely only 1 secondary there. So I do need 2 secondaries?

No, you don't need 2 secondaries. When you checked the transformer, how did you do it? If you have 4 pins, they must be connected to something. Every transformer I have like this, they are connected to a split secondary (two seperate ones). You could try looking at the spec sheet, or if you don't have one, measure resistance between all the secondary pins. You will have low resistance (a few ohms) between each end of a winding and infinite ohms between unconnected pins. This will tell you what you have for certain.

I only get resistance between the inner 2 pins. Any other way I measure there is nothing (infinite).
The writing on the transformer says: VC 5,0 / 1 / 9
And above (where the pins are) it is written: dot / zero (0) / 9V / dot

Well, I'm not sure what the writing means. Usually a dot means phase but I am not the transformer expert. This is a 9v to 230v transformer like your drawing? If your drawing is how you have it connected, you should change to the inner pins where you measured resistance.

yes the 9V transformer on my drawing is the one I´m talking about.
I already tried only with the inner pins, but didn´t work. I don´t know how many possibilities there are, but I guess many (I soldered/de-soldered many times). But then I guess I have to try again ...

I just wanted to make sure, that I definetely do not need a transformer with 2 seperate secondaries, otherwise I might be trying forever ...

thanks,
reggie

connected like that should work.

I put one wire from the Multimeter to one of the 9VAC solderpoints, the other one to the chassis,

Click to expand...

You should check the AC performance first across the transformer pins, not
referenced to the chassis.

Make sure your meter is set to AC

Do you have 9V AC across the 0/9V? pins? If so, the first xformer is OK.

Now check across the'120V' pins. You should have 120V or possibly a bit higher.

Be careful and don't electrocute yourself. Remember these are high voltages.

Stewart

Hi Stewart,

thanks a lot for your reply!
I measured across the 0/9V pins (I set the meter to AC) and there is nothing, shows only zero.

The same thing with the 120 V pins.

I have 230V going into the first transformer though.

I also hooked up the wires as in the drawing, doesn´t work. With the microphone connected I do not even get a buzz or anything.

So maybe I destroyed both transformers. I might have to go and get new ones ;-((

thanks,
reggie

Check your connections again on the first transformer. If I read this right the 120vAC should be going to your 230vAC primary on the first transformer. This will give your 9vAC output for the second transformer.

Question:

1.Do you have 120vAC at primary of transformer 1?

If yes, do you have 9VAC on secondary of transformer 1?

thanks again for your help!

I just went out and bought 2 new transformers because I thought maybe I damaged the first ones. But these do not work either! Maybe I´m really doing something very stupid wrong here (so far I only built guitar stompboxes, which are a bit easier to start with, for a newbie).

This is how I understood that I should measure the voltages: set the Multimeter to AC (600 V or 200 V) and then put one of the wires to one pin of the secondary and the other wire to the other pin of the secondary (the unit is turned on). Doing this I ALWAYS get a zero reading, on each pair of pins of each transformer.
I can only see 230V on the primary of the transformer that is connected to the mains power by holding one wire to the pin and the other wire to the chassis ground.

Now the new transformer that I bought today (the 230V / 9V) only has 2 pins on the secondary, so that should make things easier ...

I only have 230V on the primary of transformer 1 (that´s how I can read it on the Gyraf schematic), nothing else I could measure, only zero.

Sorry for all those stupid newbie questions, I only ask when I really don´t know any other way anymore ...but this is really getting soo frustrating ...I spent a lot of time (and money) building this ....

thanks,
reggie

Looking at your picture modified by Zebra 50, the 120vAC from the PCB hooks to your pin 0 and pin 230v on the primary of transformer 1. Now, don't wory about anything else being connected yet.

Turn off power between steps!

Set multimeter to ACV and measure the 120v pins on the PCB. Red lead on one and black lead on the other, dosen't matter which one with AC. You should read 120V (or 230V depending on your mains voltage). If this is OK you have power to the board, go to next step.

Measure AC voltage at pins of primary, again, red on one, black on the other. If this is OH you have power to the transformer, go to next step.

With nothing else hooked to it, measure ACV on secondary of transformer 1. You should have 9VAC with red lead on one pin and black lead on the other. If this measures OK your first transformer is OK.

Hook up wire from secondary of transformer 1 to the board marked 9vAC. Measure here to see if you have 9VAC on the board. If you do go to next step.

Hook up secondary of transformer 2 to 9VAC pins of board. Measure for 9VAC at transformer 2 secondary red lead on one pin, black on the other. If you have it, measure primary of transformer 2 with nothing hooked up to it. If it is OK your transformers are OK.

You measure step by step hooking up ine component at a time to eliminate the possibility of a bad component fowling up the whole circuit. It is much easier to troubleshoot like this. Make sure your transformers are not hooled into the circuit untill you test each side as above.

Hope this helps.

Check the things that Thomas and Viitalahde said.

I'm worried about the 230V AC to the chassis, but not between the xformer pins. Check your wiring all the way back to the mains supply. Make sure you

Is it the live or neutral side that reads 230V?

Check your fuse(s).

thanks again for all the info!

In the meantime I checked the fuse and it was blown, so no wonder nothing got through anymore. I replaced it (actually I´m using 2 fuses on the IEC inlet). Then I hooked up the transformers, step by step, first without the board connections, and I got 8 V and about 40 V measuring between pins. Then I connected to the board (the microphone was also plugged in) and I only got 7 V and 30 V.

So I figured my transformers were too weak, so I went out and this time I got 2 toroid transformers, since I read that they were better anyway. Just to be sure, I asked the guy at the shop to measure them, which he did, and he got the same weak voltages. Finally I bought one 10V / 5VA and for the other one a 2 x 15 V / 50VA (instead of 5 VA, as it says on the schematic), this combination got the right voltages at the shop.
Now I just connected them (not to the pcb yet) and I got 11 V and about 150 V. Next thing I did, was connecting the 9VAC board leads and it immediately blew my fuses. Same thing, when I connected to the 120 VAC board leads. Now I´m out of fuses, have to get new ones tomorrow ....

Yesterday I got 230V from the live side AND the neutral side. I did not check that anymore.

Could it be, that the microphone itself is not grounded properly and when it´s hooked up to the psu, that the fuse blows?

thanks for help,
reggie

The 50VA transformer is HUGE! The heater only draws about 200mA and the plate current is about 1mA. That is why the small transformers were used. If they sag a lot, that may mean there is something else dragging down the circuit, like a bad component or a ground/short somewhere.

While you are waiting for fuses, take another close look at your boards. Make sure no solder got across a trace or in a spot it should not be. Look at components again to make doubly sure the right values are in the right spot and solder connections are good. Use the OHM meter function for most of these checks, and make sure power is OFF.

Make sure capacitor polarity is correct. Make certain regulator terminals are correct.

On the mike board, make the same sort of checks. The tube pins are marked looking at the top of the socket, so make sure this is correctly hooked up. Make sure no bare wires are touching.

Now, I think your fuses blew because of the big transformer. Generally you can size the fuse by taking the total VA of all secondaries, divide totla VA by mains voltage to get amperage drawn, then multiply this result by 1.25 to get the correct fuse size. Just use the next higher value available, slo-blo for mains.

thanks for help!
So I will try again with the smaller transformers, if this is too huge (I can´t return them though, I already soldered, maybe use them for another project sometime ...)
But since I had blown fuses before, it makes sense to me now that something else is wrong too.

Now I just checked and saw that I probably put in the rectifiers the wrong way (I just soldered them in according to the white circle and the "straight side" on the pcb, without checking the polarity ;-((

I have to go out and get new fuses now and check again.

thanks for the info on how to calculate the fuse, very helpful.

reggie

first of all, the transformers are working now, so this part of the problem seems to be solved.

now I put in the bridge rectifiers the right way and I got 120V DC on one of them, the other one did not put out any DC, though I can measure 11V AC going in.

Then I had a closer look at the rectifiers and saw that they have written on them 125 and 1500R, so they´re for 125V?
I went and bought 2 new rectifiers for 250V / 1500 . I hooked them up, there´s the right AC going into both but absolutely no DC coming out of both of them.

I doublechecked all the caps, they´re soldered in the right way.
I have no clue what it can be now ;-((( maybe a wrong ground connection somewhere? The microphone was not hooked up while testing this.