Yamaha CR-800 Fusible resistor.

[Narph]

Hello, just wondering if anyone had any experience with these.

I read this post http://audiokarma.org/forums/index.php?threads/yamaha-cr-800-with-no-power-help.766295/

but I wasn't sure if he resolved his problem or not. My power supply board looks the same, had the big hw-22339 Micron resistor test out of spec, replaced with a 3.9 Ohm, 1-watt flame proof metal film resistor, powered it on, and POOF, magic smoke.

All the other fusible resistors tested within spec on the power supply board, the two on the preamp board and main amp board were all out of spec and replaced.

All the transistors (diode tested while in circuit) on the power board seem to be working, and that caps all look ok.

Voltages (pre smoke) were 12.7, -12.6, 32.8 on the power board, seemed ok, no relay click. Dunno.

Guess I'm wondering about that 3.9 ohm, and why the magic smoke? Anyone have this problem?

Thanks,

Paul

 

[mbz]

plz confirm that you are talking about FR802, 3.9ohms/1W.
You should recheck FR801, 47ohms/0.5W, all them amps must have went somewhere.

Do you have a dim bulb tester?

 

[Narph]

No dim bulb tester, I'll have to get one together. The 47 ohm 0.5W tested fine on this board, but I have another cr800 where a fusible resister was 400 something ohms (FR803? Can't make it out on the schematic), and it also had the burn marks around the Micron fusible resistor (FR807 I think? HW-22339).

 

[dly66]

Let me see if I am reading the schematic right. If FR807 was the one that burned up, also 3.9 ohm 1W, that power circuit appears to feed the protection relay circuit and the three LEDs plus the four bulbs for the meters and tuning pointer. Looks like FR802 is part of the circuit that feeds the front end and the pre-amp board (tone controls etc).

Seems to be a short somewhere in the power supply or in the circuits it feeds.

I have a CR-800 currently in the system in my living room. I can pull it out for reference. It was an auction unit that needed four new outputs (two were shorted C-E only one original good, the two fusible resistors on the amp board, and a couple fuses after replacing busted fuse holder on back panel. That and new lights, all were out. I think a soda got spilled onto the amp board. Lots of little caramel colored crystals left behind. Nice receiver probably gets overlooked in the market (undervalued).

Here is a basic diagram of the dim bulb tester. Helps keep from burning more things up quick indication of a potential short and drops voltage if high current draw. Mine has kept things from blowing up several times. Can skip the power switch and do it in one outlet box if you can get a plug in light socket. Mine more fits the diagram, all parts from HD. Not very expensive.

 

[Narph]

Thank you, that was helpful. I'll get together a dim bulb tester before I try any more power ups.

Edit Update: Built a dim bulb tester, changed the burnt 3.9ohm 1 watt fusible resistor with a new one even though the old one still tested ok. Got three new 14V dashboard lights from the local autoparts store and soldered into place.

Hooked the amp up to the dim bulb tester: bright, dim, relay clicked, everything checked out.

Seems to be working, albeit not very loud. I have the caps and will be recapping, but not until I see if I can put back together another mess I made.

Thanks for all the help guys, love this site.