Embarking on a repair - Yamaha amp power board

[oldNslo]

I'm reviewing some caps on the power board as culprit to my issue. Yamaha AV calls it a poly cap, and I see other cap constructions (like ceramic) on sites with the part I am seeking.

The service manual calls for .047mf / 630v and is noted as polypropylene.

Q1 - should I be surprised that the needed values found in the service manual are not on this (seemingly unmolested) board? I see other cap examples on this board as well.
Q2 - is there interchangeability between film, poly, ceramic (perhaps others) cap types? Or is construction type, not a concern.

Thx

 

[painttoad]

q1-no
q2-it depends (and "poly" can be interpreted as polyester or polypropylene)

i would be more likely to suggest a ceramic cap over a polyester cap as a miller cap. a polypropylene cap could be used but would be more expensive and larger.

i would be more likely to suggest a polyester cap over a ceramic cap in the signal path but would ultimately suggest polypropylene if size allows.

you also have different classes of ceramics

they aren't generally going to use polypropylene where a ceramic will do the job simply because of cost. if they used polypropylene, it's for a reason.

the model number/schematic/ location are all required for the best answer.

 

[oldNslo]

Thanks @painttoad , they are used in the power pcb, components C4, C6, C7. Parts and schema attached if helpful. Yamaha RX-V1800

 

[painttoad]

schema attached if helpful

thats not a schematic, that's board view. this is a schematic:



i can not zoom that schematic any more to clearly see the code next to c7 but the other 2 are clearly marked as polyester.

here are the codes



your parts list snip





being in arizona, i am assuming that you have the usa version.

they seem pretty specific on what they want and where depending on the electrical system.

weird how they are so specific yet do not specifically list metallized polyester. ( i am assuming metallized polyester. it COULD be metalized polypropylene but i'd bet they would call that pp.met)



mylar is a brand name of polyester so that's odd that there are 2 listings.

go with the value/voltage/tolerance that is installed in the board.

metallized polyester for c4 and c7 and mylar for c6 are what's called for.

c6 is filtering a microcontroller that is controlling power sequencing.. . personally, i'd stick to what they used because i really know next to nothing about microcontroller circuits..

i'm no e.e. so it's gonna take someone smarter than i to second guess the designer.

that's just a long way of explaining that i don't know.

but now the next person that comes along that actually knows the answer has all the info in front of them.

 

[PE9ZZ]

It's not a microcontroller but a dual CMOS flipflop. They way it is drawn (as an IC) is not very helpful in understanding what this circuit is supposed to do. What's wrong with it anyway? Stuck in standby? Happens a lot with these obscure circuits (and switchmode PSUs).

 

[oldNslo]

Thanks @painttoad , that was beyond helpful. Appreciated the boost up on the background information too. Responding to @PE9ZZ , the unit wont power up. Zero life, even after a reset attempt. I'll post a thread on this unit, as I am just starting this repair, but there are a number of these units with the capacitors in the power board being the culprit to not powering up.

 

[Hamish119]

If it's "as dead as fried chicken", C4 (22nF/630V) is the most likely cause of the issue.
See the following (he's not new to electronics);

Dailymotion

www.google.com

 

[painttoad]

CMOS flipflop

i knew that

It's not a microcontroller

i knew that too. stupid 2am fingers typing microcontroller when the brain was saying integrated circuit.

the unit wont power up.

If it's "as dead as fried chicken", C4 (22nF/630V) is the most likely cause of the issue.

if it is c4 causing the problem it SHOULD be as simple as removing it and trying to power up without it. if that's the problem, it will power up. but don't use it that way. just check for power. it'd be much safer to just test the part but i don't see how removing a shorted cap would cause it to explode.

you've got all the pretend knowledge that i have on something this new. good luck.

 

[oldNslo]

Thanks all, I especially enjoyed the Aussie accent (and regional humor), in the Yamaha vid. Just yesterday, I must have watch one (then YouTube served up 5 more) vids all on this common Yamaha AV fault in the past 2 days. All these vids had the same outcome (yaaa), but with each one, I picked up even more tips, knowledge and in some cases, a reminder to not have a messy workbench/garage (which I do) and then post on YT.

I dared not to post my "how do I fix this Yamaha" thread without fully understanding the Service Manual, review similar threads, and of course let YT guide me to what others have blazed the trail on already. Thus this "dip my toe in the water" thread about non-electrolytic caps. I have the electrolytic topic pretty well in hand, and thanks to this group, fixed my Kenwood a few months ago.

I continue to have a growing knowledge base of stereo operations, electronics, diagnostics, and can only hope this area can catch up with my 40 years of automotive repair, so to this group, I thank you for letting me learn, and coaching me along the way.

I'm off to do some component shopping after lunch today, and will update this thread with the results.

 

[PE9ZZ]

A propos Aussie accent: I read "Onslow" for your forum handle. Of "Keeping up appearances" fame...

 

[oldNslo]

Semi-familiar with the show, I only skipped past it and onto others. Mine is reference to my age, and the fact that I collect/restore vintage (crawler) tractors. If you ask me how many, I would have to ask you how many pieces of audio gear that you own.

Old n Slow.

 

[oldNslo]

Well, I'm sure all of you were rooting for C4 being the culprit, and long story short....no joy. The 3 smaller caps in scope, C4, C6, C7 all tested in spec, and none were able to bring life to the power circuit and power it on.

If this thread has run its course, then I will close this down, and open a more general, "Help me get power restored" thread that will link to this finding or if the group feels this thread should grow (but not have scope creep), I'll keep posting here.

2 groups of pics. One for C4 (widely touted as the cause), and one for C7. Separately, C6 does test in spec. Old and new parts are shown. New parts were installed. I somehow got the larger form factor caps, but can re-order if needed.

Have I missed anything in this testing segment?

 

[PE9ZZ]

Don't focus on components but on the function of the circuit. Figure out what it's supposed to do and why that doesn't happen. I am too lazy right now to do that, maybe someone else will pick up the glove. Maybe that flipflop's gone phut. CMOS and line voltage usually don't mix well.