Kenwood KAF-3030R troubleshooting. No power at all.

[StewartH83]

Hello people.

I got given a dead Kenwood KAF-3030R for free.

The unit has no standby power or anything so I've suspected its a standby board issue. It had the mains cable half cut, damaged, the natural wire cut only. Not sure if that created the problem or was damaged afterwards.

So far I have cut the mains lead down and soldered it to the pins, it gets the voltage to it. I downloaded the schematics from Hifi Engine, tried the hold source direct and press power button to no avail. I checked the voltage before the relay on the standby board which should be 13v yet only 2.6v. This makes me think its a problem before the relay. I checked the resistors, measured in tolerances, pulled out the diodes, measured good both ways. This makes me think its the standby transformer being faulty. I'm presuming the ceramic caps are fine.

I have a working Kenwood kaf-1030 yet its not remote controlled so no standby board to swap over.

I have spare standby transformers from other equipment and wondered if I could try them? I'm guessing not.
It has a microcontroller to control the input but Im guessing it's not a problem with that?

I have reflowed all suspect joints and all joints in standby board and switch board. Swapped the electrolytic 470uF cap for a working one. All fuses had continuity.

Any advice will be greatly appreciated indeed, as always, thanks for reading.

 

[Mooly]

Voltage across C551? Should be 13V ish.

Is the 47 ohm OK.

If the voltage across the cap is low then check the small standby transformer. Is the primary open circuit (thermal fuse open)?

 

[StewartH83]

Thanks for reply Mooly.

The 47 resistor measures well, the voltage before and after that resistor is low.

I'm not sure how to check the transformer. I've always respected the big transformers can kill but Im thinking the small standby transformer will be OK for me check if you can guide me please

 

[StewartH83]

I just checked for continuity on the transformer primary. Nothing. What is the chances of getting a replacement transformer for this?

 

[ubergeeknz]

Appears to be a 9v transformer, should be easy to find one in the required footprint.

Do you have a bench supply? Supply 13vdc at the point it reads 13v on the diagram, see if the rest of it works before shelling out. A 12v "wall wart" should do at a push for testing purposes.

 

[StewartH83]

Thanks for your reply and great advice.

It says 23v on the transformer

I need to get a power supply, as well as other testing equipment. I only have a DMM, DBT and hand tools atm so a PS will be needed anyway. I'll take a look for one.

Least I know there's a chance I can get a replacement and find a way to check if the rest of the unit will work. Thanks again

 

[ubergeeknz]

It says 23v on the transformer

Interesting. Perhaps just a (confusing) model / batch number or it's not the one in the diagram?

 

[StewartH83]

Yes, I was thinking it was a bit high.

A 12v supply should get it going won't it?

 

[ubergeeknz]

A 12v supply should get it going won't it?

Yeah should do, just has to pull in a relay

DC tho not AC (12VAC will make for a rather too high DC voltage)

 

[StewartH83]

REGULATED POWER SUPPLY | eBay

Will this one do? 13. 8 DCV

 

[Mooly]

Something like a small 9 volt transformer should be fine electrically and easily mountable given a little ingenuity. I would replace the 470uF cap and also the diodes, for an extra £1 or so its just not worth second guessing whether the transformer failed because of a problem with these.

https://cpc.farnell.com/block/vb2-3-2-9/transformer-2-3va-2-x-9v/dp/TF01245

 

[Mooly]

REGULATED POWER SUPPLY | eBay

Will this one do? 13. 8 DCV

Errr... really

That is massive overkill and well tbh just plain ungainly.

 

[ubergeeknz]

For testing just find the power supply off a WiFi router or similar... 12vdc

 

[StewartH83]

Great advice you two again. I can feel foolish when it comes to test equipment 🤗

I did change the 470uF cap for a used one which came from a working unit. I have a new Panasonic FR that I'll throw in it and order some new diodes from RS.

I'll look for a power supply I have and ask here if it's suitable to test this.

 

[StewartH83]

Just to be sure these are the correct diodes to order. Please excuse my ignorance as I'm learning. I've only ever ordered caps, resistors and output transistors/paste/micas previously.

6289029 item number, can't seem to share the link.

Schematic says IN4004A

 

[ubergeeknz]

They'll be fine, just common garden variety rectifier diodes

 

[Mooly]

Those are perfect. The 1N series are universally used in much equipment. Are those £0.20 each, if so then that is dear.

https://cpc.farnell.com/multicomp/1n4004/rectifier-single-400v-1a-do-204al/dp/SC14953?st=IN4004

 

[StewartH83]

Much appreciate your quick reply.

 

[StewartH83]

Thanks for that Mooly. I just registered with them yet with the charge for delivery it worked out almost £5. It's free delivery from RS. Not sure if it's because one is up the road from me in Stockport or not. I like ordering from them as I could pick orders up when needed same day.

They will be delivered quick enough and only cost £2.40 altogether for 10

 

[StewartH83]

The diodes arrived, swapped them over and put a new 470uF 25v cap in. Still dead.

I'll replace the resistors later, just to be clear and check voltages