Wanted: Kenwood PD18-20 circuit diagram

[PM3295]

People, I am in need of a circuit diagram for this power supply. The output just suddenly died. All checks around the fuses, diodes, etc. seems to be ok. This design uses a pre-regulator by phase control of two SCR's in the bridge rectifier arrangement. I scoped the control signals to the SCRs and  found that there  are trigger pulses present but no changes in firing angle by adjusting the voltage control. It appears that it stays at a firing angle to produce minimum output. The control board looks quite complex, and I would appreciate if anyone can help with a circuit for it. The front digital readouts comes on but voltage stay at zero.

I did a lot of searching on the web and found one or two links to download, but turned out to be non-functional or outdated.

Thanks in advance.

[Crackn]

just suddenly died is too vague to help diagnose it. Try to minimalize the source of the problem.. Variatuon of the mains, power surge, plugged in wrong mains voltage, some short in the output, lose wires,... After that, check for the commom parts that can fail, like capacitors, small signal diodes, small value resistors,... Check for broken solder points near heavy parts like transformers and big inductors.

Hope those tips can help.

Good luck

[PM3295]

Well, it was working the day before and the next day, there was no output at all. All the indicators on the front light up but there is no voltage output. When it was working it was not even operating near its maximum current rating of 20A. I was operating it at about 12V @ 6A, and it was fine until I turned it off at the end of the evening. There is no sign or smell of burned or overloaded components at all.

[CocaCola]

First thing pop the lid and give it the smell test, and the visual for 'burnt' or discolored areas...  Next look at ALL electrolytic caps for any visible signs of bulging, leaking or ones that just plain look 'off'...  Replace all electrolytic caps that show any signs of failure, and replace the rest that are of the same brand, especially those of the same value...

It's no secret that electrolytic caps are are pretty much the number one failure across the board in modern electronics...

[CocaCola]

I see you added some pictures, if it was me I would pull that green board up front and replace all the caps, for good measure with high end high temp equivalents...

[LzEn]

I would do the same thing as @CocaCola, even if they do not look bulged. Many times I had a similar problem with these caps looking normal but causing malfunction. It happend to me with 3 TV sets and one Audio set. So the first thing I do now when something malfunctions is aiming at the EC.

[Crackn]

Yes agree, dry electrolytic capacitors are the #1 cause for modern electronics failure...
check the pots too specially the current adjust one.

check if this manual would help you troubleshooting it.
https://www.sendspace.com/file/2n8es9

btw. avoid any setup.exe that sendspace site would send to you together with manual download.
the manual file name is: Kenwood_PD-A_manual.pdf

edit:
there is a service manual to buy. i found it when searching for pd1820 info.


good luck

[PM3295]

I am going to purchase the manual as suggested. I will post an update on my troubleshooting progress. Thanks all!

UPDATE:
It is fixed. When I pulled the control board out, I noticed a wire that broke loose from the control board edge connector to the front panel. That wire goes to the V/I check button. It appears that it was pulled or stretched by some previous work (not me) on the PSU. I re-soldered the wire and  it came back to life again. It must have been just touching there to make contact. I am also a bit disappointed; I was looking forward to some interesting faultfinding exercise.   

[Crackn]

Good to know its fixed
and don't worry, It happens to me every time.

[Gallymimu]

Yes agree, dry electrolytic capacitors are the #1 cause for modern electronics failure...
check the pots too specially the current adjust one.

You mean WET electrolytic caps?  Dry caps last forever.

I've not seen many cap failures over the years except for a brief period when bad electrolyte was ALL over the market in the 2000s which lead to a lot of consumer products failing.

I have had some audio amps from the 60s which benefited from some cap replacements though.

[Crackn]

I meant dry capacitors because of a fault and not the technology used in the production of dry capacitors.

i see a lot of problematic capacitors in many electronic devices. the market still have a lot of poor capacitor brands that fails after a couple of months.