FET "Grinder"

[dipfrik]

Could you tell us more about the psu transformer you are using?

Sven

 

[castaeplacpa]

it's the RKT 30.30 i ordered at pcbgrinder.
primary 240V
secondaries 30V

 

[Harpo]

here is my problem: the secondary of the transfomer is only providing +4,75V and + 1,5V. far from the 30V.

A transformer is AC voltage.

the primary wires are the two black ones, and the secondary are a green one, a red one, and a yellow one and a blue one stripped together. and i got these values directly from the wires of the secondaries..

measured in respect to the transformers other winding end? IE between red/yellow, between green/blue or between green/red with yellow+blue joined together ? (you measure AC voltage between the winding ends, not in reference to whatever ground,...)

 

[dipfrik]

What DC values you are measuring at the output of the psu board?
-10/+30 VDC as stated in the documentation? (see my pic)

You should never bet on psu wiring , but if i could i would bet for the secondaries:
(blue) - (red/green) - (yellow)

btw. it should be labeled clearly on the transformer outside.

 

[castaeplacpa]

problem solved, in a way, but i have 45V instead of 30.and a resistor of the PSU board apparently didn't like it, she said goodbye with little smoke.
yes i followed what's labelled on the transformer, but a wire was cutted, and well hidden..
i keep looking for mistakes.
thanks

 

[Gustav]

problem solved, in a way, but i have 45V instead of 30.and a resistor of the PSU board apparently didn't like it, she said goodbye with little smoke.
yes i followed what's labelled on the transformer, but a wire was cutted, and well hidden..
i keep looking for mistakes.
thanks

First of all - A wire was cut on the transformer?

Second - I don't see how 45V would fry a resistor here (I may be wrong), and the regulator for the positive rail is programmed to put out 30V, so there would have to be an error for it to put out more. So, I suspect something else is wrong, but just to be clear.

Are you getting +45VDC on the positive supply rail in the circuit? or are you getting a 45VAC reading off the transformer? And if its the latter, did you wire it in series with a center tap?, and what taps are you measuring the 45VAC on?

Gustav

 

[castaeplacpa]

yes a wire (the blue one) was cut inside his insulated coat. i don't know if my english is right..
anyway, i have 45V AC direcltly from the secondary of the transformer (from green and red wire, center tap with blue and yellow wires. )
i have -10V DC and + 30 DC on the output of the PSU which is ok.
for the moment i don't know why this resistor fried, i don't think it's related to the tension but there is no short-circuit on the board, so i keep troubleshooting.
the fried resistor is the one of the two located aside the diode bridge, the closest to the 4 caps.
thanks for the concern

 

[Gustav]

yes a wire (the blue one) was cut inside his insulated coat. i don't know if my english is right..
anyway, i have 45V AC direcltly from the secondary of the transformer (from green and red wire, center tap with blue and yellow wires. )
i have -10V DC and + 30 DC on the output of the PSU which is ok.
for the moment i don't know why this resistor fried, i don't think it's related to the tension but there is no short-circuit on the board, so i keep troubleshooting.
the fried resistor is the one of the two located aside the diode bridge, the closest to the 4 caps.
thanks for the concern

Maybe a picture would make it easier to follow!? The 45VAC reading makes no sense to me.

You should get around 60VAC across in series, 30VAC to each center tap. I use the term "around" loosely, and it will vary with transformers, load etc. I don't see how you are getting 45VAC, and the thoughts that come into my head are -  maybe you are measuring something else, maybe the transformer is faulty, maybe you have it wired up in an exotic way I can't think of, and maybe its a combination. In parallel, connected incorrectly, not actually measuring AC?

It would also be helpful to know which of the two resistors fried, and wether you connected the PSU board to the circuit.

We have to get this thing compressing!

Gustav

 

[castaeplacpa]

thank you for your answer
i did not connect the psu to the mainboard, i want to be shure that my power is ok before that.
the fried resistor is one of the two 100R, the closest to the caps.
here is a picture if it could help.

 

[castaeplacpa]

and there is a picture of what i get.
the two secondaries are labelled as : sek I : 30V  rt-ge                sek II : 30V  bl-gn.
so.
from red to yellow i get 38V AC
from blue to green i get 38V AC
with yellow and blue  stripped together and measured from red to green i also get 38V AC. (picture) instead of  "around" 60V AC..

 

[mus1k_freak]

Make sure you have the windings in series and not parallel 

 

[castaeplacpa]

in parallel it should be red and blue stripped together,  yellow and green stripped together.

 

[Harpo]

and there is a picture of what i get.
the two secondaries are labelled as : sek I : 30V  rt-ge                sek II : 30V  bl-gn.
so.
from red to yellow i get 38V AC
from blue to green i get 38V AC
with yellow and blue  stripped together and measured from red to green i also get 38V AC. (picture) instead of  "around" 60V AC..

Maybe your multimeters battery is low, giving maybe false readouts.
What is your (probably higher than nominal european 230VAC) local AC mains voltage for this 38.7VAC secondary readout ?

@Gustav, your PM box is full ...

 

[Gustav]

and there is a picture of what i get.
the two secondaries are labelled as : sek I : 30V  rt-ge                sek II : 30V  bl-gn.
so.
from red to yellow i get 38V AC
from blue to green i get 38V AC
with yellow and blue  stripped together and measured from red to green i also get 38V AC. (picture) instead of  "around" 60V AC..

Try checking the meter, like Harpo suggested. The secondaries seem high (I am also curious in relation to Harpos comment about your mains power), but when you get your reported readings on the separate secondaries, I wouldnt know what could be wrong to give that low a reading in the series configuration (which seems to be correct)

here is a picture if it could help.

Please check the programming resistors. It is not the cause of your resistor frying, but 330/390R seems to be swapped.

@Gustav, your PM box is full ...

It fills up fast, so I left it full. Mail is better.

Gustav

 

[castaeplacpa]

thank you
i fixed it, it was a bad contact..
now the psu works fine.
the unit is not compressing, only the dry signal with hum, increasing with the dirt pot.
so i'll stop bothering you and check my groung wiring, and study the schematic carefully.
i have a few diy projects working fine, so i'll check if i have done mistakes (grounding, wiring..)

thank you again

 

[Gustav]

thank you
i fixed it, it was a bad contact..
now the psu works fine.
the unit is not compressing, only the dry signal with hum, increasing with the dirt pot.
so i'll stop bothering you and check my groung wiring, and study the schematic carefully.
i have a few diy projects working fine, so i'll check if i have done mistakes (grounding, wiring..)

thank you again

Bad solder point, or? (Would be nice to know for future instances of the same problem)

Even with a working unit, the secondaries on the transformer seemed high. Could you give a figure "in circuit" on AC before rectification and DC before regulation? Also, check if your regulators are getting too hot to run the shop, and your previously boiled resistor.

For the circuit. So many possible problems with no further description. If you go to Gyraf's site, you will be able to find a schematic with voltages pencilled in on all transistor legs to see if the engine is running as expected.

Gustav

 

[castaeplacpa]

the wires of the secondaries are so thin that the blue one was cutted again. so even if i thought it was stripped with the yellow one, it was not the case.
yes i find the voltages a bit high, i'm closer to 71 VAC than 60 VAC.
the regulators are not that hot, i keep survey that.
the DC after regulation: -11,2 V DC and + 25 VDC (?). i'll check before regulation in a moment.

i fixed my hum trouble, got a clean signal and compression as expected, but i'll check all the voltages.

thank you

 

[Gustav]

the DC after regulation: -11,2 V DC and + 25 VDC (?). i'll check before regulation in a moment.

Check back a few posts for tighter DC values.

Gustav

 

[Gustav]

the wires of the secondaries are so thin that the blue one was cutted again. so even if i thought it was stripped with the yellow one, it was not the case.
yes i find the voltages a bit high, i'm closer to 71 VAC than 60 VAC.
the regulators are not that hot, i keep survey that.
the DC after regulation: -11,2 V DC and + 25 VDC (?). i'll check before regulation in a moment.

i fixed my hum trouble, got a clean signal and compression as expected, but i'll check all the voltages.

thank you

Any progress? And did you get those swapped resistors corrected?

Gustav

 

[castaeplacpa]

yes, i changed all the psu resistors,
everything is fine.

thank you,

next, gssl!