I am a diy'er. I am trying to rule out a 110v/50w ac power transformer as the source of my problems. One of the secondary outputs is 35v instead of 45v, regardless of the load. The vcr powers up but has issues. Also, I noticed the STK regulator has missing outputs. STK input is ok. Anyhow, is it safe to substitute the 45v line (now reading 35v), for a variac. My intention is to inject 45VAC into the circuit and observe the effect.
110v/50w AC Power transformer testing and diagnosis
- Thread starter oedipus1
- Start date
Are you absolutely sure the secordary voltage should be 45VAC? Service manuals etc... change without notice.
As you know, the secondary voltage is derived from the turns ratio between primary and secondary, this is fixed.
Assuming the transformer is reasonably healthy with no loud noises it might be ok.
If you replace the transformer with a variac you may run into earthing/grounding issues, need to check schematic.
I'd be more inclined to check voltages on power rails and at key locations (cpu???) to check they are reasonable
before considering the variac.
As you know, the secondary voltage is derived from the turns ratio between primary and secondary, this is fixed.
Assuming the transformer is reasonably healthy with no loud noises it might be ok.
If you replace the transformer with a variac you may run into earthing/grounding issues, need to check schematic.
I'd be more inclined to check voltages on power rails and at key locations (cpu???) to check they are reasonable
before considering the variac.
Yes sir. I have the service manual. The transformer has 4 different outputs. The remaining 3 outputs are ok. That is how I found out one of the secondary voltages are low. I know is rare for a transformer to fail, but not impossible. As I have replaced bad transformers, in the vcrs, in the past. When I said variac, I meant to use an automatic transformer variac that would enable me to adjust the ac voltage, for testing purposes. But, I don't know if bringing my own ac voltage into the circuit will hurt the circuit. Otherwise, no noise from the transformer. The transformer is about 35 years old.
whoaru99
Epic Member
The part about the variac is that they are autoformers so the output is not isolated from the AC power mains like the secondary winding on conventional transformer.
This can create serious problem for the gear and or for your safety as mbz eluded to with the remarks about earthing/grounding.
This can create serious problem for the gear and or for your safety as mbz eluded to with the remarks about earthing/grounding.
whoaru99
Epic Member
Not personally, but in reading here on AK the consensus seems to be (or at least my impression of it) is that pretty much any "new" STK module will be a fake. Real ones have to come from working pulls.
As well, my understanding is that some of the fakes work but usually are less robust and less reliable than the originals. Again, that's just my take on what I've read here.
As well, my understanding is that some of the fakes work but usually are less robust and less reliable than the originals. Again, that's just my take on what I've read here.
elnaldo
Lunatic Member
Yes, me, all the time. I had problem with one that oscillated at the output, but got another one and it worked OK. I've used Chinese replacements all the time and they worked fine (I mean, they didn't burn in 10 minutes, but I didn't do laboratory performance tests), and never a unit came back.
If possible, I choose the next model in the series, which usually works with higher supply voltage. But many people complains about this "copies" blowing if you crank up the volume.
For me, that's your problem. A high pin 13, 3V and above, is used to disable the voltage regulators so no 9,12V output.
Suggest you try and track down reason for high pin 13.
Also, here is a copy of the service manual. I couldn't uploaded it because the file was too big. So i am using the dropbox.
https://www.dropbox.com/s/35recbgxd5mvvoi/SLHF900 ocr.pdf?dl=0
https://www.dropbox.com/s/35recbgxd5mvvoi/SLHF900 ocr.pdf?dl=0
Apology, I've got pin 13 the wrong way around, needs to be high, fact that you have voltage out on Pin 9 indicates part of the chip is working.
Looking at the chip datasheet, equivalent circuit, voltage on Pin 9 ok, pin 8&9 connected, TR5 does not appear to be on (pin11 voltage) so no
voltage at pin 10 then pin 6. Will check the SM...
Looking at the chip datasheet, equivalent circuit, voltage on Pin 9 ok, pin 8&9 connected, TR5 does not appear to be on (pin11 voltage) so no
voltage at pin 10 then pin 6. Will check the SM...
