cr-640 help

[twc5964]

I got one of my packages in from Michael Percy. I decided to go ahead and install the some of the caps.I know for a fact I put them in properly in the power supply.Now,I have no sound period. No sound from the headphone jack or speaker jacks.

I have the dc offset set at less than 10mv on TL TR .I dont have access to my cd player but I hooked up my walkman to the aux jacks...no sound at all.

Any ideas..anyone please ?

I bought this receiver on Ebay knowing I'm taking a chance with a 28 year old piece of equipment.I installed two Nichicon kg 10,000uf 50 volt caps.The legs would not fit in the circuit board so I used 12 guage jumper wires from the bottom of the board to the legs of the caps..thats about the only deviation from anything i've done aside from installing various panasonic fm's.

This is disheartening:sigh:

[twc5964]

Checked two obvious fuses on the circuit board.Their still good.

[merrylander]

Does it come out of protect mode? If so remove the bottom plate and check pins 13 and 14 of the pre-drivers IG02950 for DC voltage. Pin 5 is the one not soldered so pin 15 is furthest from that one.

[twc5964]

Thanks Merrylander,I've got it out of protection mode now.But, the left channel is far louder than the right channel .I'm not sure where to check for this.I'm wondering if it has anything to do with one of the small 1 or 2.2uf caps i have not replaced yet on the main power board ?

I'll have to wait till I get home from work late tonite to replace those

[twc5964]

Merrylander,

Left igo2950 pin 13( -3 volts)
pin 14 (+3 volts)

Right igo2950 pin 13( -3 volts)
pin 14(+3 volts)

The right channel barely has sound ? I've looked at the service manual..maybe the problem is staring me right in the face but i'm too blind or ignorant to see it.Probably need to cut my losses here and let this one go to the dumpster and buy a preamp for my old nad amp somewhere down the road.I really wanted this to work but i'm obviously not knowledgeable enough to fix it.I cant see any burnt components on the board.:sigh:

[merrylander]

Those are normal voltages, where is the balance control set, it is very easy to get it out of position. You should feel a small click when it is centered. Don't give up too easily.

[twc5964]

The balance is centered..thats one of the first things i checked.I dont know if I have a blown transistor,resistor......dunno ! I'm obviously frustrated but i'm taking a break from it to collect my thoughts.

[twc5964]

The balance is centered..thats one of the first things i checked.I dont know if I have a blown transistor,resistor......dunno ! I'm obviously frustrated but i'm taking a break from it to collect my thoughts.

[merrylander]

When you get back to it, tap on the protection relay cover (possible bad contact) deoxit in all the switches.

[twc5964]

Okay i'll do that with the relay.I've already done all pots with Deoxit.Ironically,at work we had a piece of equipment down for two weeks.As a last resort I took the relay apart and sure enough the contacts were burnt-problem solved there.This relay is soldered into the board on the receiver.It shows no scorches on the cover though.

I noticed on the underside of the board where the right main Yamaha driver chip is- is sort of burnt...great.Mmmmmmmm...this just gets worse.I have not got to those one or two smaller caps in that section yet,however,I wish that was the only problem but I doubt it.

I consider myself technically inclined as I'm in maintenance as a profession but I have'nt worked on a receiver in years and never encountered these problems. So, this is why i'm not the sharpest knife in the drawer being able to troublshoot the problem spot on.

[merrylander]

The driver chips are still available as STK0050 II, it's the pre-drivers that are not.

[twc5964]

It's going in the dumpster soon. It's an old well used receiver.I'm tired of this thing and learned my lesson. Merrylander,let me know if you want any parts from it.I also have all the lights never installed okay.I'd like to give this stuff to someone I know can use it.I'm desoldering the new caps and keeping those. I also have the service manual purchased from Vintage Audio Manuals.

It appears someone else worked on it lord knows when ? I thought I could tackle it---not so ! Thanks for your help.. I'll wait to see if there is any interest in certain parts.I will send to those in need but I cant guarantee they are in proper working order.

I realize it might be a pot,chip,diode,transistor,resistor,capacitor,etc.. .. I honestly dont know which one.Upon first removing the bottom plate and carefully inspecting the solder joints I found a piece of solder literally connected to 2 components. It appeared to be from carelessness.I'm not exactly sure,however,I removed it--noticed nothing burnt and checked the trace for continuity of which my meter sounded off.I dont want to put any money into this.

I bought it for $66 dollars and spent close to $70 in capacitors.Hypothetically,if I was able to ressurect it back to normal I would have continued to buy parts and replace those along the way.The only satisfaction I received from it is the fact it kept me busy during my insomniac hours after work.Let me know if you need anything okay !

[avionic]

I installed two Nichicon kg 10,000uf 50 volt caps.When installing these caps,Did you install with one caps positive going to common ground and the other caps negative going to common ground :yes: or...both caps negative going to common ground ? :no: :scratch2:

[twc5964]

Each one is installed in the correct orientation.I would think if I made the mistake of reversing the polarity they would have blown right .I've changed out many capacitors and I'm very careful with electrolytics.These new caps have a black dot on the negative lug.

[avionic]

Just asking dude ..Its a common oversight..:D

[twc5964]

Oh I absolutely agree with you.I have made that mistake in the past..just not this time---I wish I did so as to help isolate the problem. I'm sorry,I did not mean to come across as being rude.

[avionic]

These things can sometimes be frustating.Just don't want to see a Yammie in the dumpster...LOL Unless you can throw it in my dumpster..:D

[twc5964]

Yes,I am obviously frustrated with myself not isolating the problem.Plus,I wanted to see just how it sounds if it was worth the effort.It may not be a lost cause.I'll get satisfaction if I can help someone else with parts if they need it.I cant afford to buy another one right now let alone locate one in better condition.