CR-2020 Service Bulletin Mods

[merrylander]

The actual service bulletins are posted here somewhere but when I have a chance I'll send them to Sigurd.

In the first photo I have removed the two screws that hold down the relay board and slid it off the six pins that connect it to the power board.

Note that in order to do this the two blue wires must be cut. Since I need to be able to lift out the power board the red and black wires must be cut also.

In the second photo I have lifted the relay board to one side to show the brackets that hold down the power board. Please note that these three brackets all heve keyhole shaped mountings, so the screws do not need to be removed, if you do remove them when it comes time to replace the brackets those nearby may well learn some new phrases.

In the third photo the brackets are out and I can now lift the power board out so that I can change the parts.

 

[merrylander]

Back again, in the first photo I have lifted the power board out and here you can see the foil side - this one is in pretty good shape. For the six pins (see them near the center) I will use a solder sucker to remove the old solder an I will resolder them fresh.

The second photo show the component side of the power board. You can see the two white fusistors and one of the 2 watt resistors (red) that must be replaced, The second 2 watt resistor is hidden under the left hand rectifier assembly.

The third photo shows the component side with all the parts removed. Oops! why did he remove the two caps? Sometimes you get a hum in these receivers and it proves to be in the pre-amp section. That section runs off 25 volts and the problem is these caps, it is easier to change them while you're in here than to dig all this out again later, so now I change them just in case.

 

[merrylander]

So here in the first photo are the old parts, those caps may well be OK but as noted earlier best to change them when you are inside.

The second photo shows the new parts in place, note that modern technology has reduced the size of caps with the same specifications. Note, it is recommended that the new resistors be mounted 1/4" clear of the board.

Third photo shows an area (circled in red) where the heat from the original parts tends to lift the foil, well thanks to the length of the leads on the new resistors it was a simple matter to bend one lead over to replace the foil.

 

[merrylander]

So, all the parts were changed and everything has been put back in place, doing the mods has got to be the second fastest four-handed game in the world.

I bought this gadget fro Micro Mark, a hobby shop. They sell it as an aid to model shipbuilders but it also works great for holding schematics.

If while looking at the very first photo you thought the rear panel looked odd, it did get bent, in shipping I presume. It is quite straight now and that is one of the reasons I keep a large pair of channel-locks.

The one fool proof symptom that a 2020 needs these mods is if the FM Tuning meter swings half-way to the left when you turn on the power. Since I used black insulated wire the final mod, bridging the two halves of the power switch did not show. It simply consists of running a jumper from the white wire on the fuse to the red wire on the switched outlet.

 

[avionic]

Excellent presentation Rob.

 

[brutal]

...and very timely given my imminent purchase of Teron's 2020... !!!

 

[avionic]

You can see the two white fusistors and one of the 2 watt resistors (red) that must be replaced

Rob are you using 1 or 2 watters for the white fusistors?

 

[Harvey/ Ga]

The one fool proof symptom that a 2020 needs these mods is if the FM Tuning meter swings half-way to the left when you turn on the power. Since I used black insulated wire the final mod, bridging the two halves of the power switch did not show. It simply consists of running a jumper from the white wire on the fuse to the red wire on the switched outlet.

Veerrrryyy Interressstinkk My tuning needle just bobs a scale division when I power on....but, one day... it'll find it's way to your shop for a tuneup.

 

[Raynald]

Hi Rob,

Do I know that CR-2020 or are those older pictures?

 

[merrylander]

Avionic, nope SB calls for 3 watt and also recommends mounting them clear of the board by about 1/4"

Ray I hope it looks familiar, the mods broght it out of protection mode but the signal quality meter still deflects to almost 100% so I need to sort that out.

 

[merrylander]

Well here is a good one for all of you Yamaha owners. Symptoms, signal quality meter would go almost full scale when the tuning knob was touched, but no FM stations would tune in. Checked the tuning head and found that the 12 volt supply was absent. Checked at both sides of the small choke coil and 12 volts was present. Turned the receiver over (that mofo is heavy) and saw that someone had run an awl or knife across the traces leading to the tuning head. Scraped off the green varnish and bridged the cut with solder. Problem solved she sings like a nightingale.

Now there is nothing inside the case that could cause this, and it is not the first time I have seen this deliberate trace cutting on CR-n20 receivers. I sure would like to know who the a**hole is, we could string him up.

I'll bridge the cuts with wire to make sure that they stay bridged.

So if you ever get this problem on a CR-n20 be forewarned.

 

[brutal]

Rob,

Sure you don't have a nail sticking up from your bench? LOL :ntwrthy:

 

[Dark Knight]

This is incredible work - I wish I knew how to do this kind of stuff. Actually, how did you learn how to fix Yamaha's?

DK

 

[merrylander]

I was repairing radios back in my early teens. My brother had setup a radio repair service and I used help him. Now this was during WW II and as soon as he was old enough he joined the RCAF. This left me to hold the fort and since there were no new civilian radios being built for the duration people had to keep what they had in running condition. Then my first 13 years with Bell Canada were in the exchanges before I transferred to the computer department in 1963.

You get the service manual, the rest is RTFM, of course knowing how to read a schematic sure helps.

 

[AltecDarpa]

It sure is amazing how packed those Yamaha's are, I remember replacing a power switch in one (probably got help from merrylander on here) and it was quite the task trying to de-solder the switch through the holes in the chassis.

 

[Dark Knight]

Rob,

That is a cool history. Thanks.

I have a good relationship with the electronics guys here at work. They always have a high school or junior college apprentice around doing grunt work. I keep threatening to apprentice with them just to learn a few things part time. They laugh but do not realize that I am kind of serious.

DK

 

[merrylander]

Every engineer doing design needs a good tech, if only to do the layout. This is probably less important with printed circuit boards, but it sure was important in the tube days and point-to-point wiring.

 

[BassoRider]

Thank's, Merrylander!
So THAT'S how you do it! :thmbsp:
I managed to get in there without cutting any wires, but it sure was cramped. By moving the transformer and the left power amp out of the way, it's not impossible.
I also replaced a bunch of components on the "top" PCB, working from below. Hard, but doable. Works fine now, and runs MUCH cooler. I'm an bona fide amateur, but found some help in an earlier thread. I'll try to replace those hard-to-reach electrolytes later...

 

[MartinJ]

One interesting observation: every electrolytic cap in any Yamaha CR-xxxx receiver I've seen has a black or green dot made with a felt marker. The cables going to the power amp boards are marked, too. Does anyone know why this was made?


Martin

 

[merrylander]

I get the feeling that the marks are the QC inspector insuring that everything is in place.