Help needed troubleshooting KA-405

pcxmbfj

Active Member
I'm hoping to bring this integrated amp back to life to pair with a KT-8005 tuner bought in '72.

Working with a hifiengine service manual until I can get one from StereoManuals whose website is being reworked.

Using Electronic Troubleshooting by Jerome Oleksy as my guide I'm ready to put the DMM on unit to isolate a fault indicated by DLB with 40w bulb.

Will testing voltage at the unswitched 120v outlet of the unit prove anything?

If I'm reading correctly only test points I've identified so far is on the PC Board schematic labeled "TP" numbers 31, 32, and 33.

Tried to attach page but between Win 10, Adobe Reader and AK limit on file size maybe later..

And see no voltage for TP.

So how do I proceed?
 
This is my unit opened.
Adobe Reader will not let me extract a page because they are password protected.
Suggestions as to where to start to isolate the short?
 

Attachments

  • IMG_0131.JPG
    IMG_0131.JPG
    128.4 KB · Views: 32
Yes, 40w bulb stays bright for several seconds. I then switch power off at the DBT then UBT.
 
i take it the relay never clicks in ?
if that's the case start by measuring voltages reference chassis ground at where the outputs emitter resistors join together ..the 0.47 ohm ones ..
 
Would those be one of the Sanken C2580 or A1105 on the heat sinks, Q19.20 or Q21.22 on PC Board?
 
yes them are the outputs ..
now find the emitter resistors ..
r47 r49 left channel
r48 r50 right channel ..
 
ph347, glad you are here.

Always admired the insight and knowledge in your posts.

I can only get a full reduced print of Power Amp PCB Foil side.

That schematic shows

Q22 has B -.59v, C -42.9v, E (no value)
Q19 has B .59v, C 42.7v, E(no value)

Are the polarities correct?

I can't get the other side to print.

Is that where I find r47, r49, r48, and r50 and where I where to place DMM probes?
 
it is the emitter values i am mainly interested in .. they should be in the mv region and ideally zero volts but that is a rare occurrence . .
the resistors are the large 0.47 ohm ones next to the output transistors ..2 for each channel .. each pair connect together in the middle . this is the place to measure the voltage in mv .
better known as dc offset .
am trying to determine if the dc offset is high as this will stop the relay clicking in .
if they are reading in voltages similar to the outputs collectors it has what is known as railed ..
hopefully this will narrow it down to one channel .or maybe the power supply .
the other readings will also be helpful .
 
Thanks so much for the guidance.

Should have a good schematic soon.

Need to study the layout further.

Got a lot to digest.
 
I've located R47..R50 and the see desired .47v, can't tell polarity though.
Are they NPN or PNP?
What is the "TP" pointed at 32 and 33?
When I test should I leave on DBT?
 
Another question, should I clean the board before testing to eliminate the effects of dust and grime buildup to DMM measurements?
CRC spray, air can, and dry.
 
leave on dbt until its fixed .
wont harm to clean it if dirty .
resistors are not polarised
tp points 31 and 33 ..are the same as where i was sending you ..so check voltages there if you like .
31 left channel
33 right channel
 
Last edited:
There's two test point on each channel if I'm reading schematic so DMM probes at TP's 33 and 32, next at 30 and 31 hoping 47V DC?

Post results here?
 
ok the problem seems to be in the left channel .
now get the voltages across each of the 0.47 emitter resistors .4 readings
 
To orient,
Left as in left on schematic? TP 30,31, 2.0-2.1V?
Does that equate as left listening channel?
 
Thanks. Sorry to be so slow-witted but I rode trails today. I was thinking the low voltage was bad but understand now.
ph347,you deserve a mentoring award.
I've located the resisters between the heat sink rails and will try to figure out how to get the DMM on them tomorrow.
Thanks for your patience.
 
Back
Top Bottom