JVC RS-33 Sound Cuts Out - Need Help for Design Flaw

[Bill Allemon]

Good day, All. I purchased a JVC RS-33 receiver back when they first came out and loved the sound, in addition to the handsome design. The problem with the unit I had was that the speaker protection circuit (I believe) would cause the sound to cut out intermittently. The same relay click that you would hear once powering the unit on, after a brief delay, would be heard prior to each cut out. Sometimes is was also accompanied by some discharge-sounding static. It also seemed like the problem happened more in winter when humidity levels were low (I'm in Detroit).

Fast forward three decades and I decided to purchase a replacement RS-33 through eBay, but this unit has the same problem. Since three time's the charm, I purchased another vintage unit and it also has this issue.

When I originally purchased my first unit, I took it back a few times to have the problem fixed. Both times the technicians said they fixed it, but they didn't.

It appears that this might be a design flaw with this particular model or series of receivers from JVC. I'm thinking that there's a grounding or shielding issue in the output circuit that's the root cause. I have tried all the obvious fixes; made sure there wasn't a stray speaker wire touching an adjacent post, trying different speakers, using contact cleaner on the slider pots for volume etc.

Is anyone familiar with this problem? Any ideas on the cause or a possible fix? I've search the forums and it seems like others have this unit, or one from this series such as the RS-77, that operate without any problems.

Any insight the group can provide would be most appreciated. Thanks in advance.

 

[Tom B]

I haven't worked on a JVC R-S33, but have worked on the R-S77, which should be similar.

First off, it is unlikely to have the same issue with 3 units. Are you using 8 ohm speakers?? as this unit call for 8 ohm. Using 4 ohm speaker could cause the protect circuit to engage.
Secondly, make sure your connections are good, and that each speaker you are using tests at 8 ohms

Third, and here is where the design flaw may come in. This JVC series uses the "Super A" Circuitry which caused many of the power tab transistors to run very hot, causing cold solder connection on the board where the transistors are connected. (2SD669, 2SB649 etc). These issues can be seen with the amplifier transistors as well as the ones used in the regulator power supplies.

 

[Bill Allemon]

Thanks for the quick reply and the thoughts. Now that you mention speakers, I remember that this cutout problem happens even when speakers are not connected, like when I tested the two replacement units I purchased. Or when I powered up my old original unit and it started cutting in and out before I could connect speakers. Sometimes the cutout happens right away when the unit is cold and other times once it has warmed up. When I do connected speakers, I use my Bose 301 Series II bookshelf speakers.

I'm thinking that these units had a manufacturing flaw, like the cold solder problem you mentioned. Is there a way to confirm a cold solder joint, other than visual inspection?

 

[redk9258]

I wouldn't call it a design flaw. More of a maintenance issue. I doubt anyone thought these would be around 35-40 years later.

 

[Bill Allemon]

Except that this problem happened out of the box when I bought my first R-S33 in 1980. This issue would come and go. But when I noticed that my replacement units had the same issue, that's when I figured it was either a design flaw or a manufacturing quality problem.

Seems like it is either a grounding issue or a cold solder joint. Each time it happens, you can hear a static sound coming through both speakers that grows in amplitude until, CLICK! the speaker protection circuit trips. Sometimes it will clear and sound will be restored until the next event. Other times cycling power does the trick. And still others, it won't come back to life until you're ready to try again another day. Right now, I don't even bother hooking up speakers. I can plug any of these units in and listen to the protection relays tap dance.

Until I can figure out what the root cause is, my beloved unit and its replacements will have to sit in my basement audio museum.

 

[redk9258]

I would start by measuring the DC offset at the speaker terminals. Better yet at the emitter resistors because they are before the relay. The relay is likely doing it's job. If you decide to go inside, get mini grabbers so you don't slip with a probe and short something out.

 

[H2-Engr]

Start out your search by reading US Patent 3,691,427 of Sept 12,1972. The amplifier is a series of direct connected (no capacitors) transistors. Any fault in any transistor results in an amplified fault at the output which would destroy your speakers if not for the cutout relay. I never got to get a service manual for the rs33 but do have for the 77.
I was getting no sound at all until I balanced the initial current flows in the amplifier. I am still searching for the elusive fault component but, I don't give up easily. I like the low background noise. I also have a later class A JVC a RX-809 VTN and it works great. The big problem I have with finding the faulty transistor, it fails intermittently. I will look at solder joints though as suggested. Good luck!

 

[sregor]

Used to see them with this problem due to a loose screw, which grounds the amp board. Clean and tighten them. I believe it's a "star" ground, so one of them will be the culprit.

 

[dr*audio]

Yep, some JVC amps and receivers used one of the screws on the back panel that secure the input jacks for a ground. The screw gets loose and the amp goes into protection.

 

[stvlush]

My wife got a R-S33 after college in the 70's. A few years ago it started cutting out as described by the OP, so we retired it. Last week I got it out of storage, and gave all the pots and switches a good cleaning with Deoxit. It seems to be working fine now. Can't point to a specific component because I cleaned them all, then tested. Might have just been the jostling around that fixed it, but a good cleaning is almost always worth a try with old gear.

 

[Macdaddy]

Hmm that is an odd problem. I just picked my second one up last week and gave to my daughter as a present for Christmas. cleaned circuit board and did de-oxit on controls. Let it play for 3 hours and all was well. However when screwing the wood case back on I did hear some slight static in speakers from the screws which i thought was weird. The one i bought 4 years ago was used in our bedroom and played fine with no issues. My step-daughter now uses in her room.

 

[JoshuaMonger]

Yes on the main amplifier board tighten the top left most screw if the amp clicks and cuts out. I also had issues with the loudness button and softly putting pressure on it can change the output. Now Im up against a battle with a 50hz hum in the built-in phono stage. I have 2 of these, and already recapped the power supplies electrolytic capacitor on the trouble unit and to no avail, even checked the grounds and replaced a few caps on the phono stage. No clue!

 

[tomasdcm]

Hi everyone!!
I have a JVC RX-805V and I'm having the same problem described by Bill Allemon on this thread. I'm looking all around the internet trying to find which is the origin of this flaw, and hopefully ideas to fix it and not give up.
Thanks for any comments and help! It's great to have a place to discuss this issues

 

[dr*audio]

Hi everyone!!
I have a JVC RX-805V and I'm having the same problem described by Bill Allemon on this thread. I'm looking all around the internet trying to find which is the origin of this flaw, and hopefully ideas to fix it and not give up.
Thanks for any comments and help! It's great to have a place to discuss this issues

Tighten the screws on the rear panel and those that secure the PCBs.

 

[tomasdcm]

Tighten the screws on the rear panel and those that secure the PCBs.

Hi @dr*audio ! Thank you so much for the fast reply! I followed your advice but the problem remains . I opened the receiver, I couldn't get to all the PCBs screws as there are many and some very hidden, but i tried tightening up everything I could reach (I didn't any really loose). I would love to try any other possible solutions you (or other members of the sorum) can suggest . If pictures or videos could help, I can upload this material. Thanks a lot!

 

[dr*audio]

Hi @dr*audio ! Thank you so much for the fast reply! I followed your advice but the problem remains . I opened the receiver, I couldn't get to all the PCBs screws as there are many and some very hidden, but i tried tightening up everything I could reach (I didn't any really loose). I would love to try any other possible solutions you (or other members of the sorum) can suggest . If pictures or videos could help, I can upload this material. Thanks a lot!

Did you tighten the screws on the rear panel? All of them?

 

[tomasdcm]

Did you tighten the screws on the rear panel? All of them?

Hi @dr*audio !! Sorry for the delay on my response. I think I have finally found a "workaround" for my problem and I hope it will be useful for someone else on the future. I followed your advice but the problem remained, I was loosing my hopes on the receiver but I tried once more.

What I did different? I turned ON the Dolby Surround mode. It sounds very simple and that's why I didn't tried it before, but I found hope on this mode because it made a similar sound as when the receiver turns ON, and the same sound I was having while listening to music as described before. Probably using this mode music "bypass" the component that is having the problem when Dolby is not turned ON.

Thanks for your help @dr*audio! Having someone giving me a push was great to keep on trying different solutions and ideas

 

[Bill Allemon]

FYI. The actual problem on the R-S33 is a flaw in the speaker protection circuit. I recently found through research that JVC knew about the flaw and issued a Service Bulletin in 1982 to technicians in case customers complained about this very issue. The solution is replacement of a resistor with a different value and installation of a jumper wire from one point in the circuit to ground. Modification instructions can be found in the Service Manual at this link which also contains the Service Bulletin. The download costs about $14 but is worth it to get factory instructions on the proper repair.

JVC R-S33 Service Manual, Analog Alley Manuals

 

[tomasdcm]

Thanks Bill for the information! Finally my "workaround" was just an illusion and the problem appeared again after some hours of testing. Everything looks like the same problem you had on the R-S33, and it was one of my main ideas, a component/design flaw. Now the problem is how to know which resistor that has to be changed and where to install the jumper. I downloaded the Service Manual and User Manual (just in case) but none of them talk about this issue and I can't identify the speaker protection circuit. If you or someone else have some final ideas, it would be great

Service manual can be downloaded for free here: LINK
Instructions manual can be downloaded for free here: LINK

 

[Bill Allemon]

Unfortunately, that will be a challenge since your receiver was made approx 10 years after mine. So the fix will be different. The only option is to study the schematics of both and see if you find any similarities to help identify component and location. If you're not comfortable with the schematics, I'd be willing to study both for you, if you want to post a copy of yours.

FYI, I also have an R-S77 with the same issue, so I'll need to see if the fix will be roughly identical for that unit.