KA 7300 resistor mismatches schematic

[zig2zag]

Hi All,

I embarked on restoring a garage sale (10$) ka7300 and this is my first ever posting. This puppy smells when plugged in and 1 weak channel and other is dead. Currently have power supply board out, replacing caps and diodes. Now looking at resistors.

Issue 1:R1 has a 270 ohm (2 watts?) but schematic wants 560 ohm-2 watts.

issue 2: R2 has 180 ohm 3 watts but schematic wants 330 ohm 2watts.

Any history I need to know of changes in this model or is this simply someone slammed whatever in there?

my guy feeling is to correct it. Thoughts ? thanks!
zig2zag

 

[rschweitzer]

Suggest you do a query here on AK to review what others have done with this amp in terms of issues, restoration, etc.

As for schematic values over what is installed, the first question is what does this impact? i.e., voltage/current. Are these values already correct?

I use the installed values unless there is an issue that is either known or I uncover. Example, in the KR-8050, I could not dial in the Bias to factory spec. After reading about the issue here on AK, the schematic called for the correct value, while the installed value was wrong. After some re-calculation, problem solved.

 

[avionic]

my gut feeling is to correct it.

Lots and lots of undocumented manufacturing upgrades and changes were made after the service manuals were published. Some service bulletins were issued to correct and document the changes in the service manuals. A lot were not.
I always go with " what is currently installed " over the schematic drawing and parts lists. Unless it is 100% obvious that the part in question is not OEM..
I suggest you do the same.

Key is to look at voltages at pins 12 and 15. Are they equal in value ? Like +/- 24vdc or within +/- 5 %..

 

[avionic]

but it looks like R11?

Voltage dropping resistor for the LED.. Carbon or metal film would suffice. Not a critical audio path.

 

[zig2zag]

Suggest you do a query here on AK to review what others have done with this amp in terms of issues, restoration, etc.

As for schematic values over what is installed, the first question is what does this impact? i.e., voltage/current. Are these values already correct?

I use the installed values unless there is an issue that is either known or I uncover. Example, in the KR-8050, I could not dial in the Bias to factory spec. After reading about the issue here on AK, the schematic called for the correct value, while the installed value was wrong. After some re-calculation, problem solved.

thank you, yes I’ve learned quite a lot from queries on this Model but at times it’s overwhelming (due to my lack of experience.) i decided to just dive in. Immediately saw the zener diode warnings to replace and sure enough one of ‘em looked like ate too many mashed potatoes. I hope to get some voltage readings in near future. Thanks for insights and reply!

 

[zig2zag]

Lots and lots of undocumented manufacturing upgrades and changes were made after the service manuals were published. Some service bulletins were issued to correct and document the changes in the service manuals. A lot were not.
I always go with " what is currently installed " over the schematic drawing and parts lists. Unless it is 100% obvious that the part in question is not OEM..
I suggest you do the same.

Key is to look at voltages at pins 12 and 15. Are they equal in value ? Like +/- 24vdc or within +/- 5 %..

Thank you! Im in for some more fun when I power this puppy up. Appreciate the key voltage insight!

 

[zig2zag]

To echo @rschweitzer and @avionic, there are isolated exceptions, but the general rule of thumb is whatever value you pull out of the board, you stuff back in.

That said, I'd replace all carbon composition resistors with metal film replacements because cc resistors can drift quite a bit over time. I can't see it because of glare, but it looks like R11? on that PS board is an example.

Thank you! Good tip to know!

 

[zig2zag]

Voltage dropping resistor for the LED.. Carbon or metal film would suffice. Not a critical audio path.

Thank you! Another good item to know!

 

[Semanon]

Do you have a dim bulb tester (DBT)? It will be helpful when starting up. Lot of threads available with a quick search.

 

[zig2zag]

Do you have a dim bulb tester (DBT)? It will be helpful when starting up. Lot of threads available with a quick search.

Thx! Not yet! Yes I saw many references to using one. That’s on my must have list to make before I plug this back in, especially being a newbie. I might have a fire extinguisher handy too!