CR-800 in protection and no tuner

I picked up a non-functioning CR-800 today for almost nothing. It is in wonderful cosmetic condition, but is stuck in protection mode. It powers on but the relay does not engage and the tuner seems to be non-functioning as well. I am unable to get either meter to deflect at all while moving through the FM range. AM is also non-functional.

I've cleaned and applied De-Oxit to all controls including the coupler switch. I adjusted bias and balance as per the service manual. The fuses are all good. The output transistors show no gross faults (I did a real quick test). Tapping the relay does not cause it to engage.

I was hoping it was going to be one of the easy things I've already tried .. I'll have to dig deeper and verify that correct voltages are getting to all boards.

Is it possible that the protection mode and non-functioning tuner are due to the underlying issue?

-Matt

Need to start at the power supply.Verify its putt'n out 100% and getting to the correct points of use.Like the amplifiers,tuner and protect circuit. Check fuses-verify + & - 12vdc power supply is working.Its used in both the Tuner and protect circuit.
Fuseable resistors (fuses) in the power supply circuit.


http://sportsbil.com/yamaha/cr-800-sm.pdf

Thanks Avionic. I'll have to get deeper into this thing. I'm getting 45V off the main caps, but I haven't traced it beyond that.

I love this series of Yamaha gear. I have a CA400 on my desk at work that I use every day with a pair of headphones. It's an awesome piece.

-Matt

Check what Dave suggested and also do an ohmeter test between the ground connection on all boards. Had one in here once that had the ground connection missing between amp and power boards. Caused all kinds of strange reading.

Thanks guys!

I just checked out the main power board. +/-45VDC at all the test points, as expected. I also have what appears to be a 37V supply (markings on the board indicate 33V). But I have no 12V - zippo, all test points read 0V. So the lack of a 12V supply is most likely the problem. I just need to figure out what happened to it. It looks like I'll have to yank that main power board which doesn't look like a good time.

ML - I'll double check all of the ground connections.

-Matt

Check the voltage at the collector and at the base of TR804, with respect to ground.

Yes, it appears that I have +/- 25VDC just prior to T804, T805, T806, and T807, but nothing after these transistors. These guys may be the problem ... I need to test more and will measure voltage at collector and base as you recommend ecluser.

Do these transistors commonly fail on these units? I just hope I'm not chasing a red herring.

-Matt

TR804, base to ground = 1.126VDC, collector to ground = .585VDC. I have 25V across C815, just preceding TR804. The only thing between C815 and TR804 is a string of zeners. I need to take a hard look at the schematic now .. I'm not sure why I'm not seeing more voltage at TR804.

-Matt

Did you check the voltages on both sides of FR803 & 806 or pull those resistors and check there resistance?

I need a better copy of the schematic, I can barely read the one I downloaded here. What value are FR805/806? It looks 1/2W 47 Ohm, but I'm not sure because I can't tell from the schematic if that is for FR805 or FR803.

Are those resistors or fusistors?

By the way, thanks for the help guys - I really appreciate it!

-Matt

PS - I'm going to have to put this project down for a week or since I'll be travelling next week for work. I'll get back on it next weekend. I hope I can get this piece up and running again!

FR805 or FR803.

Click to expand...

Merrylanders schematic is a little clearer .It looked like 805 to me too.But its actually 803 I was refering to. I corrected my posts.
http://www.audiokarma.org/forums/showpost.php?p=4243399&postcount=46
Fuseable resistors
FR803 47Ω 1/2 watt
FR806 220Ω 1/2 watt

Consult this thread

http://www.audiokarma.org/forums/showthread.php?t=338721

There is a much more readable schematic of the power supply on post #46

You will see that C815 is related to the negative supply. You have to take the voltage at C814

Thanks ecluser! It's a shame there was never any closure to that thread .. seems very similar to the issue I'm having.

-Matt

use a dim-bulb tester for power up trials... saved my bacon on a CR-600 today! Probably would have saved rpampt's cr800 when he blew the fuses too.

Here's my CR-600 thread

Thanks guys. One last post before I head out for a week of work away from home.

I found one of the two fusistors to be almost open - I didn't measure it out of circuit, since my soldering iron and bench gear is currently packed away. In any event, in circuit it measured .5MOhm (of course that doesn't mean much). It is marked 40447 on the board (yellow, violet, black, silver = 47 ohm) so this is FR803. I measured 25VDC on one side and essentially 0 on the other side ... this may be the culprit!

The other fusistor, which I can only assume is FR806, had expected voltage on both sides, so that one seems OK. It measured a little high resistance wise, in circuit, but not too bad.

This leads me to a few more questions:

1. I see that many people just replace the fusistors with resistors .. is this the recommended solution?
2. What is the likelihood that this fusistor is the sole problem here? Is it possible that a downstream transistor failed causing the fusistor to open? I see no char marks on the board, so nothing catastrophic appears to have happened.

Thanks again guys! I've been slacking on building a dim bulb tester .. I need to get on that, would be very helpful in many cases.

-Matt

OK - real progress! I had a 1/4 W 47 ohm resistor in one of my junk bins, so I bypassed FR803 with this resistor using micro clip leads, powered it on, and voila! Relay clicks and tuner works!

Is it acceptable to just use a standard 1/4 W resistor here, or should I hunt for an actual fusistor?

Thanks again guys - really appreciate all the help!

-Matt

Update: Although the relay clicks and the tuner appears to work (meters deflect and I can tune in to strong station without an antenna, I do not get any output through a set of headphones. I've tried the tuner input and an mp3 player through aux input, and neither produce any audio output. So it looks like I'm not out of the woods yet on this one.

It is not only permissable to use resistors in place of those &^%$ fusistors, it is recommended.

Good, now wiggle the coupler switch on the rear panel back and forth and see if that brings sound.

Outstanding!
Other problems can't be to serious if you are getting a single relay "click".:thmbsp:

Update: I installed the new fusistor and the relay now clicks and the tuner comes To life. It tunes well according to the meters, but the stereo light does not come on. I don't know if the lack of a stereo light is just a bad bulb or soemthing else. I plan to track that down later.

The larger issue i'm now facing is that I am unable to get any sound from the pre outs. I tested the amp portion using another preamp into the main in jacks. The amp works and sounds great. I've cleaned all the controls again and have fiddled with the coupler switch, but haven't any luck getting the preamp working.

Are there any common issues in the preamp sections of this series that I should look at?

Thanks!
-Matt

Perhaps a very dirty input selector switch? Or that coupler switch on the back.

Just a shot in the dark...