If you know what the output is supposed to be, look for a signal of the right frequency being generated by the ICs, then follow that signal to the link to the pads. At some point, the signal probably will vanish on that path. The path may go through ICs, Transistors, SCRs, etc. You'll need to look at the datasheets for the parts to determine what is input and what is output.

I use This site for datasheets, they have about everything and it is easy to navigate.

 

If you know what the output is supposed to be, look for a signal of the right frequency being generated by the ICs, then follow that signal to the link to the pads. At some point, the signal probably will vanish on that path. The path may go through ICs, Transistors, SCRs, etc. You'll need to look at the datasheets for the parts to determine what is input and what is output.

I use This site for datasheets, they have about everything and it is easy to navigate.

Thank you!

do you think i can follow the path with the DMM or a need an scope for that?

 

A DMM set on the right range (depends on what you are looking for, try DC and Hz) can get you through most things that run at lower frequencies (<20kHz), unless it is a very inexpensive one.

 

A DMM set on the right range (depends on what you are looking for, try DC and Hz) can get you through most things that run at lower frequencies (<20kHz), unless it is a very inexpensive one.

thank you for your help.
i'm following the path, and i'm not getting voltage at base of transistor NPN (pic attached).
The chip has Voltage at Vdd. it's a CD4068BE. sorry but i have no idea how that chip works.

 

It is an 8 input AND/NAND Gate So the output K (pin 1) is high when all 8 inputs are high (AND), output J (pin 13) is high when all 8 inputs are low (NAND)

Not sure which output is being used, or if both are.

 

It is an 8 input AND/NAND Gate So the output K (pin 1) is high when all 8 inputs are high (AND), output J (pin 13) is high when all 8 inputs are low (NAND)

Not sure which output is being used, or if both are.

i was checking again and, yes i'm getting voltage, the pin used is 1, i'm getting mV because of the 2.7K resistor next to the transistor base. now after that, i get lost. collector goes to pulse transformer

 

That's a single layer board. You should be able to draw the schematic in one or two days. From there on it will get much easier. Think you can do that? Starting with the power supply and the output part.

 

That's a single layer board. You should be able to draw the schematic in one or two days. From there on it will get much easier. Think you can do that? Starting with the power supply and the output part.

i can try...there is always a first time!

 

a friend in another forum drew a schematic of the output section pretty accurate.

 

i drew this mess, is helpfull in any way to find out why there is not signal at the SCR gate????
the pulse transformer drives the SCR gate. right corner down of pulse transformer is ground and left corner downgoes to gate.

 

Can you extend that schematic to include the Logic ICs, SCR, Transistors, and resistors?

 

Can you extend that schematic to include the Logic ICs, SCR, Transistors, and resistors?

i can try, but i dont know if you are gonna be able to see anything in that mess!
do you think the problem can be the pulse transformer? if i put DMM between base and collector of that big transistor i get voltage, but i dont get voltage between catode and gate of scr.

 

What are the Gate, Anode and Cathode of the SCR connected to? The photo is rather blurry, and I can't make out part numbers.

 

What are the Gate, Anode and Cathode of the SCR connected to? The photo is rather blurry, and I can't make out part numbers.

there you go!

 

Do you have a photo of the top side of the same area that is not blurry so that the top/bottom can be matched?

 

i'm taking more with no flash that way the traces can be seen trough

 

more

 

Is there a jumper wire soldered across both leads of the resistor in the upper left of this photo? Why is there such a clump of resistors/solder in that one area as well.

Also, The jumper on the bottom of the board (mentioned earlier), was that present when the unit last worked?

 

The resistors that are "standing" are in series, it looks like the guy run out of space there. those ones are also in parallel with the small one on the left. and the wire just below the resistor goes to the green cap.
about the jumper, i dont know if it was there when it was working,
but the other machine my friend has, it doesnt have that bridge there, so i took it off. it's shorting out a diode, it doesnt make any sense

 

Hi!

i've been working on the schematics, i have the output side already

Thank you in advance!