CR-820 In for a dial string and other items.

[Blue Shadow]

First off, the dial string was broken an inch to the left of the dial indicator so it gets a new string. But to get there I have to get the tuning knob off (for other cleaning and such), while I wait for dial string to arrive.

I have the two set screws out of the tuning knob and it damn near won't turn even with some oil in the grub screw holes. Prying with spoons will bend the faceplate. Dental Floss, not going to happen.

Anything I can do to hasten the removal short of flame? Maybe soldering heat will work if i can get the iron in that space. Maybe I need some liquid wrench in the grub screw holes.

This unit is from a smoking home so it needs to be pulled apart and cleaned and the string replaced then the switches need a deoxit treatment before I evaluate it. Relay clicked in 3 seconds and both channels had sound. Without a complete recap what will keep this unit running another dozen years? Maybe just that relay timing capacitor I've read about? Any other must do work other than a complete recap? Thanks.

Please check back, I'll have more issues with this fine machine.

Here is the victim:





You can see it does need some cleaning.

 

[Blue Shadow]

OK here is how to get that damn tuning knob off. Although coming in and writing the above gave the oil a chance, there is nothing turning in that area.

Remove the two screws holding the thin rod inside the tuning mechanism that connects the tuning knob to the counterweight. Rotate the knob and rod (remember this is stuck) separately from the counter weight and remove the counterweight. Now continue to rotate the knob against the resistance of the glooogrease used when the unit was assembled on the rod inside the brass bushing until the knob with rod comes out of the receiver. Now you can work on the tuning knob at the workbench in the metal, wood and auto shop and not on the electronics bench.

In this lousy picture the counterweight has been loosened and removed, replaced for the photo op. You can see the rod that is not wanting to come out of the brass bushing, not shown, that it rides in. This rod needs cleaning and relube for another few years of smooth troublefree life. Sony used the same glooogrease on the STR-V4 that had the same problem but I think its tuning knob did come off.

 

[Blue Shadow]

Now that the faceplate is off we can look over what is there. 40 years of dust that just settled into the unit. It needs a good cleaning. Maybe tomorrow if it doesn't rain too much, this is an outside job. Last pic shows that pink/purple 33µF/16V cap used for the relay timer. I guess that is getting replaced.

 

[Blue Shadow]

@avionic, are there any gotchas or special replacements that need to be done when recapping this unit? It is getting a full recap, cleaned, transistors reseated, and the other normal refresh steps. Recommendations welcome.

 

[avionic]

Pretty straight forward.

 

[Blue Shadow]

Cap List cause everyone wants to see a cap list.
1 each .1 50
3 each .22 50
1 each .47 50
2 each 1 25
11 each 1 50
2 each 1BP 50
3 each 2.2 50
2each 3.3 50
1 each 4.7 10
1 each 4.7 35
1 each 4.7 63
11 each 10 16
2 each 10 25
1 each 10 35
2 each 22 25
1 each 22 50
4 each 33 16
3 each 47 6.3
2 each 47 10
2 each 47 16
3 each 47 25
1 each 47 35
4 each 100 6.3
2 each 100 10
2 each 100 16
2 each 100 35
2 each 100 50
2 each 100 63
2 each 220 6.3
3 each 220 16
2 each 470 6.3
1 each 470 25
1 each 1000 50
2 each 10000 50 these are 35 x 85mm and you won't find any like that. they are also 15mm spacing for the leads again NLA.

Guess I'm going to go with a bit more on both voltage and capacitance for these big uns. This because many of the larger caps today are delivered at 10% lower than value, well within the ±20% range. The higher voltage is because we are using a bit higher voltage today than back when this unit was built. So a 12000uF 63V cap should be fine, just modding things so it fits.

 

[Blue Shadow]

Well the unit is coming apart nicely, once one figures out how to remove the glued in PS caps without breaking the board.

The relay in this unit looks fresh. Here is a pic of one of the contact sets that close when the relay engages.



Clean enough to eat off of it, but it is less than ¼" in diameter.

 

[Blue Shadow]

Well over 80 caps replaced, large PS caps cobbled into the unit and the frame around them adjusted to fit. Changed the bias VRs and set the bias today, got the unit cleaned over the last couple days and will be putting it back together.

Checked the main voltages, 27.something should be 30
and the three 12 volt points were 11.8 or so and a ±12.28 I guess. Hope these are close enough for Yamaha word or do I need to make some changes in the other parts of these circuits? Upped the main caps to 12000/63 a small bump up from 10000/50 to account for the new caps ±20% and usually being on the lower side of the specified size. And they are a decent size, so they look right.

 

[Blue Shadow]

Restring this thing is a pain so far. Looking for hints and secrets. Maybe I just need to be better at using thread.

 

[Blue Shadow]

While looking at web shots of the tuning string, I found a video that shows a refresh of this unit. Showed a single cap hidden behind the transformer. There is a 1" wide chunk of circuit board on the outside edge of the unit that holds the transistor socket connections. One small cap near the end of it. Transformer has to come out to get to it. That was a quick swap, one I would have missed if I hadn't been doing some more research. Being a 1µ/50V cap it might have been on of the small ones that must be replaced. Whatever it is done. Not to get that restring done right.

 

[Oldsansui441]

Yes l also remember a few "hidden" components beside the transformer on this model. All the best with your restring, hope you can get it sorted.

 

[Blue Shadow]

Yes l also remember a few "hidden" components beside the transformer on this model. All the best with your restring, hope you can get it sorted.

I think that is all it took, someone to hope I got it going right. Tuner string is in place and working properly. Lots of variables in that set up. Tuner capacitor start and stop location, orientation of the pulley on the tuning capacitor and the position of the tuning dial. All have to be right for the system to be set up correctly. A bit more work since the drive gear and shaft fell out of this one when messing with it. Thanks for the comment.

 

[Oldsansui441]

That is great to hear, sounds like your perseverance paid off. No doubt there was lot's of variables with it. Yeah not sure about the CR-820 but some other receivers/tuners l have worked on don't even use a circlip to retain the tuning capacitor drive shaft or gear.

 

[Blue Shadow]

With the drive gear shaft coming out, I was glad to have this pic of the unit from before cleaning.

Made it possible to realign the physical stops in the right place. Other issues for those that might...the pulley on the tuning cap needs to be positioned properly to get full end to end dial pointer movement/tuning cap movement with the specified tuning string length and the dial pointer needs to be positioned once everything is back in place. A lot of items need to line up go get the tuning string back on correctly.

 

[KingBubba]

For future reference, The dial strings are 30# braided Dacron fishing line. A light coat of bea's wax will make them stickier.

 

[Blue Shadow]

Well the unit is restrung for the too manyth time.

Since this is a full recap to make the unit last decades more, a cleaning to make it presentable and such, I like to tighten things up a bit inside and out.

The cabinet has 30, yes, Thirty threaded pieces to tighten with the cabinet off the unit.
12 for the two top grilles, 4 on a tab that fits into a bracket on the receiver, 8 for the bottom grille and 6 for the feet. The unit is held in the cabinet with an additional 5 bolts with the square washers that grip the unit and spread the force. That is a lot of hardware. But early gear in the vintage era did use more hardware than later units.

A total of 87 caps were counted following the work, with one hiding behind the transformer, mentioned above. This is more than the list above but the additional caps were the same as the large quantities values listed and I bought a few extras of those, so there were available. The main ps cars required a mod to the bracket that keeps them in place but that wasn't hard, just bent it to reach a bit further and lowered in on the back panel to fit the shorter caps. Then installed a couple rubber plugs for the now unused original holes.

Interesting feature to make the dial indicator work properly, there is some monofilament strung across the bottom of the tuning dial to keep the pointer sliding freely across the dial without touching it. Nice. You can see this line in the third pic above showing the dirty dial area.

This unit had a hitch in the volume control down low. Lost a channel at some low volume setting and just didn't work smoothly. This is probably due to the concentric balance control and the difficulty with removing the knobs pulling the shafts too much. Robisme had one on the bay and we struck a deal and I got it installed.

Putting everything back together, needing a pint of paint to lock all the fasteners as was done when new. Need to finish it up as I picked up a Pioneer SX-828, well Dave and I did, at the fest yesterday. Dave was going to bring it here first anyway, now at least I can claim part ownership. It has three extra switches installed on the rear panel to figure out. Should be fun.

CR-820 pics to follow

 

[Oldsansui441]

Sounds good, looking forward to your photos.

 

[Blue Shadow]

So let's put some pictures in here. From above the before pic in the cabinet

and of course, we need an after, not in the cabinet, yet.

It got a lot cleaner.

Getting to all the parts, the bottom braces and the bracket holding the large caps in place were removed.

You can see the relay and the knobs box and the two side to side braces and one front to back brace. The relay was evaluated and pictured above with no visible pitting. Using this one again.

Here is the unit before removing the big caps. Standing tall next to the transformer and held by 5 pins soldered in place, only two are electrically connected, glue and the bracket. Unit still dirty, an early pic before the work really started, showing the broken turner string.


This unit got something cleaned or recleaned every time I sat down with it. Here are the before and after of the tuning capacitor as it goes from furry to metallic.



Here is the solder side without the braces and ready for work. In this shot you can see the solder pads for the large caps and further over the circuit board on the other side of the transformer that needs to be moved to change a small 'lytic cap.



Some disassembly, notice no tuner string, making it easier to work on the unit. One large cap removed.


Here is the unit after install of the smaller Higher Voltage and Higher Capacitance PS caps. Bracket has been lowered on the back panel about an inch and the vertical section of the bracket from the top rear to the section that holds the caps has been bent to a slanted position to hold the caps properly. This bend moved the bracket out a bit further, needed because of the mounting location of the new 2-pin, snap-in caps. These were installed with one pin in the correct solder pad location (for polarity) and the second pin needed a hole drilled in the board and a jumper used to connect that side of the cap to the circuit. The caps were also glued in place to keep them from working loose from the board.



In the above you can see the VRs used (blue below the transformer, the dial string installed, probably third attempt, the fourth was a keeper, and a pile of new smaller caps installed.

 

[Blue Shadow]

I said a pile of parts not counting the four light bulbs we have the following:


The volume/balance control had an issue the new one seems to work just fine. Thanks @Robisme

Here is a close up of the large cap install.


The two original holes in the back panel to mount the bracket were plugged with a couple rubber plugs I had in my parts bins. I have not idea what they were for or from. They are Yamaha parts now.
Here is the work done that I can remember:

MECHANICAL REPAIRS AND UPDATES
Unit disassembled and faceplate and knobs washed.
Large capacitors removed and glue removed.
Circuit boards cleaned.
Tuning knob assembly disassembled, cleaned, lubricated and the bushing tightened to the chassis.
Tuning capacitor cleaned externally and contacts cleaned.
Cabinet cleaned.
RCA jacks cleaned and polished to remove corrosion.
Rear panel components cleaned and polished.
Tuning dial cleaned.
All cabinet screws tightened.
All chassis screws tightened.
All controls cleaned with electrical contact cleaner/deoxidizer and lubricated as needed.

ELECTRICAL REPAIRS AND UPDATES

All electrolytic capacitors replaced.
Transformer removed to access a single electrolytic cap for replacement and retorqued in place
Large power supply capacitors were slightly relocated to accommodate their different size and lead spacing. The bracket holding the taller originals was modified to fit the new caps and mounted lower on the back panel to properly hold the new capacitors. These capacitors were glued in place to help secure them to the board.
Heat sinks were removed and cleaned.
Power transistors and mica insulators were removed and cleaned.
Heat sinks and power transistors/mica were reseated/reinstalled with new heat sink compound.
All lamps were replaced with proper, currently available lamps. Dial pointer was modified to provide lighting similar to the meter lamps.
Volume/Balance control replaced.
Idle current variable resistors replaced and idle current set to service manual setting.
Tuner was restrung and dial pointed installed per the manual.
All fuses were checked for value and signs of stress and either reinstalled or replaced with correct value fuse.
Mechanical fasteners received a dab of paint to hold them in place as was done when new.
Unit was tested and adjustments verified.
Burn in for a few days


Maybe I can get a finished shot of the unit in a day or two.

 

[Oldsansui441]

Great job, very nice work indeed. I like your repositioned filter cap bracket, looks like it was meant to be. Thanks for all of the photos .