Yamaha RX-730

[ve ze]

Yes, it should be. The rectifies are down the path. But it still not showing any AC voltage.

 

[mbz]

With amp powered off/unplugged check resistors R230 & R232, probably one is open.
Power on the amp, connect black probe to pin 9, select 20Vac scale on MM, measure Vac one side of R232, repeat for otherside. Measure Vac at pin 10.

 

[ve ze]

Unplugged: R230 - 308 ohm, continuity - OL; R232 - 5.1 ohm, continuity - beep; R 231 - 14 Mohm, continuity - OL;
Power ON: pin 9 (black) to pin 10 Vac = 0; each side of the R232 Vac = 2 mV ac;

 

[Nashou66]

Unplugged: R230 - 308 ohm, continuity - OL; R232 - 5.1 ohm, continuity - beep; R 231 - 14 Mohm, continuity - OL;
Power ON: pin 9 (black) to pin 10 Vac = 0; each side of the R232 Vac = 2 mV ac;

What about voltage AC on either side of R230?

Nashou

 

[mbz]

Power ON: pin 9 (black) to pin 10 Vac = 0;

Does not look good

R230 - 308 ohm

My SM has R230 as 1ohm 0.25W flameproof. Can you check for any markings/post a pix however measurement suggests toasted.

R232 - 5.1 ohm

SM has 4.7ohms 0.25W so ok

R 231 - 14 Mohm,

Failed open, replace, post pix, sm has 1ohm 0.25W flameproof

 

[ve ze]

These R230 and R231 look not pretty. I'll try to locate the replacements. 1 ohm 0.25 W flameproof. Is flameproof the same as Metal Film Resistor or Carbon-Film Resistors?
Something like these? https://www.mouser.com/ProductDetail/KOA-Speer/MF1-4CL1R00F?qs=61XiPJbgCR0dwBrE/u7jPQ==

 

[ve ze]

What about voltage AC on either side of R230?

Is that as in one probe on pin9 then measure Vac on one side of R230 and again for the other side?

 

[avionic]

Is flameproof the same as Metal Film Resistor or Carbon-Film Resistors?

Yes and No.. Key is Flame proof coating like these. As long as the datasheets clearly specify flame resist, proof or retardant.

https://www.mouser.com/ProductDetail/SEI-Stackpole/RNF14FTD1R00?qs=FESYatJ8odK3P84xMJwQnw%3D%3D

https://www.mouser.com/datasheet/3/1099/1/SEI-RNF_RNMF.pdf

 

[ve ze]

Am I right assuming that the bulb requires 15 Vac?

 

[Nashou66]

Is that as in one probe on pin9 then measure Vac on one side of R230 and again for the other side?

Yes.

 

[mbz]

Am I right assuming that the bulb requires 15 Vac?

Power ON: pin 9 (black) to pin 10 Vac = 0;

First need to sort out why you have no Vac between pins 9 & 10

edit looks like pin 9 & 10 are halfwave rectified giving 15.9Vdc so 15Vac wont do it.

 

[ve ze]

First need to sort out why you have no Vac between pins 9 & 10

Okay. The replacement resistors are on the way.

 

[Nashou66]

What about voltage AC on either side of R230?

Nashou

Have you done this yet?

I didn't see a result yet.

 

[ve ze]

Not yet. R230 is bad and it's up for a swap in a few days, so I will do that check right after.

 

[Nashou66]

Not yet. R230 is bad and it's up for a swap in a few days, so I will do that check right after.

You can still check the one side, just to make sure the transformer is ok

 

[ve ze]

... just to make sure the transformer is ok

Trashed transformer would be devastating. I wanna put off the bad news if any.

 

[mbz]

You can still check the one side, just to make sure the transformer is ok

Okay. The replacement resistors are on the way.

Don't see the resistors fixing this.

Yeah you could do further testing on the transformer. Measure Vac between 7&10 repeat for 8&10

 

[ve ze]

Measure Vac between 7&10 repeat for 8&10

Zero for both.

 

[Nashou66]

Zero for both.

Can you give a larger area of this part of the schematic? More to the right and top, but keep the tranny in the picture?

There might be a circuit that keeps that tranny off until another circuit is engaged. I don't have the schematics to check.

 

[mbz]

Zero for both.

I hope I'm misreading the schematic...

With amp powered off/unplugged
Measure resistance between pins 7&8 then 8&10 then 7&10
OL on any of these is bad. Check the solder on these wire wrap(??) posts