Kenwood KR V7070 AV receiver - Page 1
Forum section: electronics / repair

author: Specmaster
author_rank: Super Contributor
timestamp: August 06, 2018, 11:22:48 am
content: Guys, I have recently acquired this receiver and the seller just stated it as "died one morning".I was expecting something like power supply issues fuse blown or dodgy caps etc but everything there seems to be in order, the display lights up ok, the AM/FM tuner seems to be working just fine as do all the other inputs and the unit can be controlled via the IR remote just fine but I'm unable to get anything from either the speakers or the headphone socket.I have downloaded a couple of service manuals for this but unfortunately the the scanning process of the schematics has managed to clip chunks of the schematics off. These schematics appear to be spread across multiple pages so I'm guessing that the original was on an A3 sheet that pulled out and opened up to reveal the full drawing and there are chunks of this missing.Does anyone have a good copy of this manual that I could borrow or know where I could obtain a good copy with the all the information contained in it please?

author: David_AVD
author_rank: Super Contributor
timestamp: August 06, 2018, 11:41:06 am
content: Have you checked if there is any audio on the record output?Can you hear any hiss / hum from the headphone / speaker outputs?Is the speaker relay clicking in like it should a few seconds after power up?

author: Specmaster
author_rank: Super Contributor
timestamp: August 06, 2018, 11:47:34 am
content: Quote from: David_AVD on August 06, 2018, 11:41:06 amNo I didn't think to check for the presence of a signal on the tap recorder outputI'll check that later.There is zero hum or hiss from either the headphone socket or the speakers and the relays for the A and B sets of speakers can be heard operating when selecting either set of speakers, not sure about the main relay, I'll also check that later.

author: drussell
author_rank: Super Contributor
timestamp: August 06, 2018, 05:57:20 pm
content: Do the amplifiers actually have their + and - railsat the amp?It sounds like probably not.... That, or some protection relay is faulty or something...

author: Specmaster
author_rank: Super Contributor
timestamp: August 06, 2018, 06:12:34 pm
content: Problem is that the schematics appear to have about 1" or more of the drawing shopped of at either end so you can't even line up buses etc as they may have been turned through 90 degrees so they are not useable.

author: Specmaster
author_rank: Super Contributor
timestamp: August 09, 2018, 08:43:45 pm
content: Update on the progress so far.Thank you everyone for your input and the answer to the various suggestions is as follows.The power amp does indeed have its power rails intact and the speaker protection relay is working just fine. I had to move it off the bench in order to tear down my latest acquisition, a Tektronix TDS210 DSO and check the state of the power supply for bad caps etc and it was all fine. This is back together and working.Popping the Kenwood back on the bench and plugging in some headphones and switching, and hey presto the tuner was working and it seemed so was everything else, I connected a meter to the speaker terminals, removed headphones and the speaker terminals were powered up just fine.I then set about poking here and there and twisting the chassis and it went dead, then came back to life and went off again, this was when I was moving the audio input boards and also the video boards. It seems that these being plugged into each other via extended header pins, these also plug into the main amp via more edge plug/sockets so the problem appears to more a bad contact on one or more of these plug/socket interfaces.So now I'll have disassemble this section and do a though clean up of connections and then assemble and check again.When I've done this I'll come with a further progress report but in the meantime I'm still looking for a decent copy of the service manual for this if anyone could assist here it would be a great help as the ones on the internet for down don't tell the whole story and the schematics have junks along the extreme edges of the pages chopped off in the original scanning process.

author: David_AVD
author_rank: Super Contributor
timestamp: August 09, 2018, 09:07:17 pm
content: As well as cleaning the connectors, it can be worthwhile resoldering them as well. Cracked joints on headers is fairly common, especially with single sided boards.

author: Specmaster
author_rank: Super Contributor
timestamp: August 09, 2018, 10:06:37 pm
content: Yeah, done that already, couldn't see any bad joints looked very good and all were shiny. Connectors were caked in dust and fluff so I'm hoping it's all OK now, Wont know till tomorrow when I put it all back together again, I have to go and pick my son up from a wedding reception as his girlfriend was going to do i but he can't contact her, probably zzzzzzing

author: coromonadalix
author_rank: Super Contributor
timestamp: August 10, 2018, 12:25:11 am
content: All the manuals i've seen are shifted in the diagrams, but they are still usable to follow an signal path or sense any audio coming out of the rca plugs (preamp section) you could even take phono plugs and make some induced noise by touching the center pin with any small screw driver ...

author: Specmaster
author_rank: Super Contributor
timestamp: August 10, 2018, 12:38:26 am
content: Making some noise isn't the issue, I have plenty of signal generators that cover the audio bands for that as well as a built in radio tuner. What I need is the schematics to be complete, if not for now as I think I have the problem pined down, but for the future. I always like to have all the manuals for my gear and if and when the time comes to sell it on, the manuals go with it to the new owner.

author: coromonadalix
author_rank: Super Contributor
timestamp: August 10, 2018, 12:47:45 am
content: If i had all the services manual for my things i would be happy too ... ask some Kenwood service center if you can buy originals or copies of the services manuals and come back to tell me your journeyTried once too many for my Sharp, Sony, Samsung, did manage to find some of them, had a few Service manuals leaked too, some service shop are very "protectives"Would be nice to other members to know what you've "pinned down" to maybe help some others in the future ?

author: Specmaster
author_rank: Super Contributor
timestamp: August 10, 2018, 01:05:47 am
content: We need to have a database where we could stick copies our manuals for all members to take advantage of

author: David_AVD
author_rank: Super Contributor
timestamp: August 10, 2018, 02:16:15 am
content: Check out the HiFi Engine web site. They have manuals.

author: tautech
author_rank: Super Contributor
timestamp: August 10, 2018, 02:19:50 am
content: Quote from: Specmaster on August 10, 2018, 01:05:47 amTake your pick out of the file repositories in this thread:https://www.eevblog.com/forum/repair/repair-documents-and-links-sticky-me-please-mods/My fav is EBAMANhttp://www.ebaman.com/index.php/remository

author: Specmaster
author_rank: Super Contributor
timestamp: August 10, 2018, 08:03:37 am
content: Quote from: David_AVD on August 10, 2018, 02:16:15 amThat's where I got the 1st copy from. It seems that those that they have all got it from the same source. They are all bad scans with the same info missing.

author: Specmaster
author_rank: Super Contributor
timestamp: August 10, 2018, 11:07:01 am
content: Update on the repair.After removing all the plug in audio and video cards along with the tuner (not the easiest of tasks) cleaning and resoldering all the joints around the interconnections and reassembling it all again, it seems to be working just fine now so I'll just leave it running on a soak test for a while. Thanks to everyone for tips etc.

author: Chris56000
author_rank: Frequent Contributor
timestamp: August 13, 2018, 06:35:50 am
content: Hi!Is this one any better? I believe the circuit-diagrams are all there complete, altho' you might have to refer to the copies with incomplete diagrams for easier-to-read parts lists!https://www.dropbox.com/s/vds7o2n0k9aqclc/KRV7070_SM_KENWOOD.pdf?dl=0Chris Williams

author: Specmaster
author_rank: Super Contributor
timestamp: August 18, 2018, 08:58:47 pm
content: Quote from: Chris56000 on August 13, 2018, 06:35:50 amYes Chris this is much better thank you.I had thought that it was repaired but it wasn't after all, after moving the amp and switching on again the intermittent crackling etc was back.I striped it right down and removed the main PCB from the case and after looking over the joints with a microscope I noticed what looked like suspicious joints on IC1 and IC2, these are mounted on vertical heatsinks in the middle of the board and gently rocking the heatsinks revealed the extent of the problem, almost every pin was able to move despite giving the illusion of being perfectly soldered. Out came the soldering iron and some fresh solder was applied to all pins and bingo the problem was resolved even picking the amp a couple of inches and dropping on to the bench couldn't cause a loss of signal. Perfect.

author: tautech
author_rank: Super Contributor
timestamp: August 18, 2018, 09:13:32 pm
content: Cool, nice fix Spec.The only thing that might annoy you some is the 'structural' design engineers overlooked that stress on the heatsinks could crack the solder joints. One wonders which planet they were on when they signed it off as ready for production.

author: Specmaster
author_rank: Super Contributor
timestamp: August 18, 2018, 09:27:50 pm
content: Yes I spotted that they didn't bother with any form of mechanical support / fixing for those heatsinks, relying on the IC pins only. I pushed the IC's down as I resoldered the legs and now at least the heatsinks are resting on the PCB so they are a little better supported now. I did think about applying some hot snot to them but decided that if they had to be removed at any point in the future that the snot might pull of some traces / pads during the removal stage so I decided against that.