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Yamaha CR-820 - guidance and possible help needed

JorgenSWE said:
+30 pin measures +27.4V
-12 pin measures -13.8V
+12 pin measures +12.3V
+12M pin measures +12.3V
Click to expand...
These are probably ok, they match the nominal values.

JorgenSWE said:
TP 1 = 36.6V
TP 2 = 36.6V
Click to expand...
Not good, excessive voltage, amp is in protection mode, 36.6V is near rails voltage so probably a shorted transistor.
Next step is to diode test likely candidates TR719, TR723, TR725, TR721. Try incircuit first, amp powered off, looking for a c-e short.
If TR's pass diode test then need to track/hunt down the source of the 36.6V, measure dc voltage at,
*** +ve and -ve voltage rails at main filter caps
*** R763 (either side to GND)
*** R765 (either side to GND)
*** D711 anode or cathode
*** D705 cathode
 
Hi!
Thank you! I will look into the testing of the transistors. Possibly on wednesday. Have to do some maintenance at our local radio station tomorrow evening. Might take a couple of hours. Have just recently installed a new comprsssor and it need some tweaking. Also check on a fiber link to our town hall.

I will report back when I have had them tested.
 
Hi!
Managed to carve out some time during my lunch break. Did a quick measure on the transistors you mentioned. The TR721 has a short between c-e both in circuit and out of circuit. TR719 seems ok.

Measured also the output transistors behind the transformer. Both seems fried. Mesured between the casing and the two pins. It gave a shortcircut between the casing and one of the pins on both, but shifted leg when meauring the other transistor. But I guess that is normal, as one is NPN and the other is PNP.

Guess I need to order some new transistors. Where is best place to order?

When ordering, is there anything else I should consider swapping? Like relay, other transistors or other components. Fuser resistors etc.

Tnx!
 
JorgenSWE said:
Measured also the output transistors behind the transformer. Both seems fried.
Click to expand...
Best to remove outputs and test out of circuit to make 100% sure, some low resistance in circuit paths.
Suggest also check emitter resistors R771,3,5,7 (0.22ohms, so expect about 0.5-0.7 with probe resistance)
Also check R779, R781,3,5 (0.47) alond with FR701(68), R759 and R761.

JorgenSWE said:
Guess I need to order some new transistors. Where is best place to order?
Click to expand...
Ideally somewhere like mouser or digikey however freight to Svergie would probably be prohibitively expensive. Avoid the bay, too many fakes. Maybe a local electronics shop however avoid if it looks like a "front" for chinese gear
 
Hi!

Well, as it so happens to be, I live in Sweden :). So Mouser is a good choice for me. I will order and report back when I have swapped the components.

Anything I need to observe when swapping the transistors? Only change the those fried or do both channels?
 
Check those other resistors mentioned in post #24, they may have been stressed. Also check R763,5 (4.7ohms).
TR721 blowing may point to bias circuit TR707,9 and VR701 or TR711,3.Test all these. I wouldn't rush with an order, need a better idea of root cause/failure sequence. Include some (20?) KSA992 for the differential pair TR701,2,3,4, can be problematic/drift and cheap as chips though not the cause in this case. Tempting to replace the bias trimmers with multi turn types but then where do you stop... best to get unit working before deciding if refurb is needed/wanted...
 
Hi!

Ok, sounds like a plan. Will do some more research, looking to measure the resistors you mentioned. Got some work cut our for me. Will report back asap. Cheers!
 
Hi!
So I have, to the best of my ability, tried to measure what you suggested. Transistors have been tested out of circuit. Resistors also or with one leg desoldered from the pcb. It has been a bit hard to make out what and where each component is placed, but I do think I got it right. Might have missed something, but can if needed redo that again.

Here are the results:

TR 707 = Broken
TR 709 = OK
TR 719 = OK
TR 711 = OK
TR 713 = OK
TR 721 = Broken
TR 723 = Broken
TR 725 = Broken

R767,9 = 471, 474 ohm
R761, 759 = 1.73k, 1.57k

R763 = 21.8 ohm (red color)
R765 = 21.9 ohm (red color)
R771 = .09 ohm (green color)
R773 = .18 ohm (green color)
R787 = .12 ohm (white color)
R791 = .15 ohm (white color)

R779 = .40 ohm (white color)
R781 = .40 ohm (white color)
R783 = .39 ohm (white color)
R785 = .39 ohm (white color)

R759 = 1733 ohm
R760 = 1508 ohm
FR 701 = damaged, no reading on ESR

Tnx!
 
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Looks like failure of TR707 took out the other components. Replace failed parts then power up on DBT.
Need modern day subs for the following,
TR707 2SC458ecb, replace with KSC1815ecb
TR721 2SA814bce, replace with ??? MJE15033bce overkill?
TR723 2SD427 replace with MJ15024?
TR725 2SB557 replace with MJ15025?
FR701 68ohms 0.5W replace with something like mouser 71-CMF5568R100FKEA (flame retardent)
mount standing off board in clear air.

My transistor matching is fairly basic, maybe others can give better subs...
 
Hi!
Thank you for your reply. Yes, there's quite a few components that has failed. I will order what is needed and replace them. Once that is done I will report back here. Thank you for your help.! Much appriciated!
 
Hi again!

Just a quick question. Based on the mesured resistor values, do they need to be replaced as well? You did not mention them specifically in your reply, but I wwwould assume they need to be replaced as well.
 
Been a bit busy, looking a bit closer at the resistors...
R761(1.5k) measures a bit high 1.73k, greater than 10%, might be early signs
of stress. Yeah, I'd replace.

R763,5 (21.x) should be 4.7ohms, remeasure out of circuit and replace if more than 10%
out of spec. R771,3, 787, 791 all look low which is unusual, possibly replace the battery
in your multimeter or test with another unit.
 
Hi!
I changed battery in the multimeter just prior starting this project. Measured with both an analog and digital multimeter They are also measured with ESD meter, also with a fresh battery. So I don't think it is the meters.

I'd rather change all the resistors, it is not a huge cost, than having issues later. I want a good stable unit.
 
Hi!
Well, a few things came in my way, work and family related stuff. I'm trying to place an order on Mouser, but wanted to update myself on what I need to order. Especially the resistors. The 0.47 ohm seems to be a backorder on Mouser until next year. But I'm not quite sure that I have looked at the correct product(s).

Is it too much to ask of you (or anyone else reading this) to reply with a link to the correct products, especially the resistors that you see (see my post #28) a need to replace. I would like to include as much as possible in this order, without doing an "over kill" as far as replacing components that might not need to be replaced, but to still be on the safe side. and I do want to avoid ordering the wrong stuff. I have noticed when poking around that many of the transistors have "black legs". Swap or keep?

also noted that Kcs184 has a backlog, not in stock until june, can that be substituted for KSA992 that is in stock?

Once again, thank you for your time and expertice. Much appriciated!
 
Haven't tinkered with a CR820 so working off the parts list,
In stock mouser part numbers

R759, 760 1.5k 1W (metal Oxide) 603-RSF200JT-73-1K5

R771,3 0.22/1W
71-RS01AR2200FE12

R763,5 4.7/1W (metal film, flame retardant)
71-CPF14R7500FKE14

R779, 781,3,5 0.47/2W (metal film?)
71-CPF3.475%T00 CPF3R47000JNB14

FR701 68 0.5W 71-CMF5568R100FKEA
Could not find fusible so opt for metal film with flame retardant, mount standing off board.

Probably could do better on the 0.22 ohm emitter resistors.
 
Thank you guys! Ok I will check the other vendors as well for the out of stock transistors. Anything else that is worth having at hand that I shoud include in the order? Like the relay or varable resistors? I get a free shipment, so I don't pay anything extra for having that included in the order. Only the cost for the components. The money part is not an issue :)
 
JorgenSWE said:
Hi!

Greetings from Sweden! I'm new here and new to old Yamaha receivers. This is also my first post. A while back I managed to lay my hands on an CR-820. It was bought an online thrift shop. It was a long shot, since I did not know about its internal condition, but what caught my eye was the outward condition was close to mint, looking at the pictures. So I went ahead and bought it. The intial prize was about 260 USD. However, as it turned out it was basically "dead" upon arrival. The only thing lighting up was the red diods, no sound from the speakers nor the headphone jack. Beacuase of this I managed to negotiate it down to 60$, since it basically was a non working unit that they had sold to me. If that is a ggod or bad thing remains to be seen.

I have read up on refurbisihing this kind of receivers on this forum. From what I have understood, this can be related to the protection curcuit being engaged. I have ordered a refurbishing kit to swap all the capacitors, starting on on the power supply and working my way down to the amplifier section, one bit at a time until the whole unit is done. Of course also clean the pots and push buttons. Also using a DBT. My intital question to this forum is as follows.

Are there any useful test I can do prior to starting the swapping process?

What other general recommenations do you have that would help me as far as determening what is wrong with the unit? Or, is the best route to start swapping components right away and see what happens? I do have some basic knowledge in electronics back from my school days, so I can work a multimeter etc. I do not have an ocsilloscope at this point.

Thank you for guiding me through this!
Click to expand...
Hi Jorgen, it sounds like you've accomplished a lot in the last month and a half. One thing I didn't hear anyone ask is does the relay click over when you power it on? If the relay is not switching you wouldn't get any output from the speakers/headphone. Regardless, it sounds like there are a number of parts that needed replacing anyway. Did you test the lamps to see if they aren't just burned out? If they are, you might want to replace with LEDs. You'll get a nice glow from an otherwise dim faceplate.IMG_3013.jpeg
 
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