Hi All

Just thought that I would post a little story of the progress I have made with my JVC M-70. About five weeks ago I won this machine on ebay. (Some of you will be aware of this, I was pretty chuffed with the fact that I had won it and that I hadn’t paid too much for it.) The machine was sold as faulty, low volume. Piece of cake to fix, I thought. It looked good in the auction pictures too. So, with baited breath, I awaited the arrival of this beast. A week later on return from work I found a large parcel sitting forlornly in the garden. It had been raining and the outer packaging was as soggy as Madonna on a good day! I dragged it indoors and the other half protested at the fact that I’d made the carpet wet. With some great enthusiasm I unpacked the parcel and there it was. A nicotine stained mouldy relic from the past. It did not look as good as the auction photo’s. I cleaned it up a bit before I posted pictures of it on s2g. The photographs I had taken made it look better than it was! I was beginning to wonder what I had done.

          After I had photographed it I then powered it up. It had been in the warmth of the house for a good three hours by this time (I never like plugging old gear in straight away, always like to let these old things acclimatize, in hindsight maybe I should have left it overnight but I was slightly impatient. I don’t think it would have made any difference anyway.) When I switched it on I found that indeed the audio output was quite. The radio could be heard at a very low level with the volume sliders at maximum. I turned the tuning knob gently going up the medium wave band and heard as nasty snapping noise. The radio was stuck on Radio 5 Live; the tuning cord had appeared to have broken! I then turned my attention to the tape deck. .The first observation was that several of the music search l.e.d. ‘s were illuminated randomly.  The auto stop solenoid actuated as soon as I pressed play and smoke billowed from the unit! Holy shit I thought, this is not a good start. I then went to bed and had very bad dreams about big scary monsters (This is possibly a side effect of listening to too much David Bowie)

          The following day I decided that I would strip this heap of crap down. This is what I found -

1. A chassis mounted plastic pillar that formed part of the tuning mechanism had snapped. The little pulley that sat on the pillar was rattling round in the bottom of the machine; the tuning cord was all over the place.

2. The ferrite rod antenna was dangling by it’s delicate connecting wires due to the fact that it’s mounting lugs had snapped.

3. The machine had a strong burnt resistor smell.

          For some reason the tuning cord issue annoyed me the most. I found a picture of the inside of the M-70 on s2g and spent the next couple of hours repairing the tuning mechanism. I drilled a pilot hole into the chassis and used a self tapping screw with a rubber sleeve on it to replace the broken pillar; re-threaded the cord (which was a tricky and annoying task!) and all was well. Rather better than I had expected in fact. I then looked at the rest of the machine and decided that it was time that I got myself a service manual. An internet search and £8 later I had one. It was not the best of scans, but it was a start.

          The next day saw the task of finding where the smoke had come from. As I said earlier pressing play cased the auto solenoid to activate instantly, so I disconnected it. There motor wasn’t running, no volts on it. I traced this back to the main board. The 12v voltage regulator transistor X505 (a 2SD439) had blown taking R517 (a 2.2 ohm 1 watt resistor) with it. The resistor was badly charred but luckily it has long legs that spaced it from the main board and a heat resistant sleeve on it. There was no damage to the P.C.B.

I ordered replacement parts from ebay. Several days later they arrived, I fitted them and the tape deck sprang into life. Re-connecting the auto stop solenoid caused the shut off problem to re occur though. This problem was down to IC 602 being faulty. (This is the auto stop drive chip) Ebay again provided a replacement chip, another problem solved.

          The next issue was the music search L.E.D. ‘s. The voltages round the MMS control chip, IC631 weren’t making sense so this was the next I.C. to be replaced.   No more random L. E. D.’s but things still weren’t happy in the music search area. It now didn’t do anything but illuminate the first L.E.D. when you switched the music search on. Oh well, onto the next problem.

Low audio output; cased as it transpires by a permanent audio mute state. The way this machine works is simple in principle. The music search board sends a mute signal to the amplifier when skipping tracks. This signal goes via the auto stop control P.C.B. There are several logic conditions that put the machine into mute mode. There are at least six transistors that are involved and the last one in the chain was stuck at hard 12v, muting the amplifier. I had to isolate each section of circuit bit by bit to see what was switching the mute on. Three hours of work tracked it down to a very obscure fault. It was a short circuit l.e.d. This was causing a bad logic level that was switching every transistor in the mute circuit on. I have never before come across an L.E.D. that has gone dead short; it must be due to age. Replacing this caused full volume to be restored. However this fix uncovers another yet fault; an issue with the volume sliders! But that is for the next post! 

The above picture shows the location of X505 and R517 the 12v regulator for the motor drive and it's associated resistor.

Ferrite rod re-attatched to chassis with a couple of tye wraps

This picture shows the repair to the tuner cord pulley mount.

This shows the location of the fault auto stop driver. (I.C. 202) (Upper square, please ignore the lower square!)

This picture shows the offending short circuit L.E.D. that caused the mute problem

These are the components I have used so far.

I think this box went to the right home and I'll bet the seller had tried to have this fixed but was quoted a fortune by a tech! Most of us would be delighted with the bargain price then opened it up, given it the once over and cleaned up the switches etc then back on ebay with it! Look forward to seeing the end result! how are you getting on with getting the spares you were looking for Seb?

very informative write up good stuff seb .

Cheers mate

Sorry smeats, I tried replying to you and it got stopped by the bl***y moderator filter! This is getting to be a bit of a pain!

Sounds like you know what your doing seb...btw where do you live mate isn't wales by any chance lol

Know what I'm doing!! Nahh! Sorry I don't live in Wales, but it is a place I would like to explore one day! (I have visited the Brekon Beacans)

If you knew what you were doing... you wouldn't have bought the m70 haha JK

wow..echo what Si says,good work Seb!

if i knew where my m70 was seb she would be yours....working sliders etc....sadly long gone you can ask northner about that

Tee Hee

Cripes Seb you really know your stuff...I think the majority of us would've accepted defeat pretty quick with this one...I know I would lol

Glad I got mine from Lee instead of eBay!

Sounds like this M70 has a good chance of booming again

Cheers guys, this has been one labour of love so far; and it isn't over yet!!

Well done seb!

Cheers smeats  I have orderd some sliders from 4your home, a JVC parts supplier. I am not sure that they will come up with the goods though. Delverence very kindly made me aware of a thread on which a member wanted to trade parts. I'm waiting for them to get back to me. A lot of you have made some very good suggestions re the volume sliders. I have a few options. Thats about it really.

Cripes Seb you really know your stuff...I think the majority of us would've accepted defeat pretty quick with this one...I know I would lol

Glad I got mine from Lee instead of eBay!

Sounds like this M70 has a good chance of booming again

I would have acepted deafeat on this one. Well Done Seb!!!!!!!

If I ever lay my mitts on a sick M70 I'll have to "import" you to do the repair!

Massive respect here   be great to see it up ad running again

You are a genius. Hats off to you.

And a big thanks for narrating the troubleshooting so well.

Wow this box needed a lot of work! Amazing how so many defect can occur in a single box! Thanks for writing it all down Seb! It's very informative!

Sort of good news for the new sliders. I contacted the company about the status of the order I did a month ago and they told me to hold on, they will come    

Thats very good news, I will jump for joy if the sliders turn up! This machine has been a total basket case; the worst I have ever tackled! I think both of us could do with a lucky break, you have been waiting a long time for those prts.

Thanks to brutus, thebaron, AE_Stereo, Si, Docs, Michiel and everyone ellse on this thread for your interest, help and kind words.

Seb you seem to know what you are doing !!

I call this a ressurection back from the nearly dead

Cheers deech, I know a lot more about these now than I did when I started. Problem after problem with this one!

Definetly need some luck now! Today I worked on my replacement workhorse for the M70. Some kind of aka of an aka box, dont know the name out of my head lol. And just when I finished it I cut the wires of the cassette head in two while closing the box... Argghhhhh! 

Really hope the sliders turn up and ASAP  I mis my outdoor M70! Got more of them, but they are to good to take outside. Did you already open the sliders en tried to fix them? Gonna try to do that next week. Again... The company was talking about 30 working days, so have to be patient for the new ones I guess..

No I havn't opened the sliders yet. I have put the machine to one side at the moment and am currently working on my second CS-600. The rougher one of these will be my work horse machine. Just replaced the belts and found that the tape playback is slightly low on the left hand channel. Knackerd head! Very worn! I could have sworn it looked ok on initial inspection, must be loosing my eyesight or my marbles (or both!) Worn heads are not a problem though, just a little more work. Aiwa CS-600 is a very simple machine compared with the M-70.

Sorry to hear about your head wiring, thats a bit of a downer and a most anoying thing to happen just as you are finishing off a repair job. When things like that happen to me I just put the machine to one side and tackle it again the following day! Anyway good luck with it mate.

Looks like all will be sorted soon then seb...thats Great news...seriously i wish i had skill like yours mate...nice one

Cheers Reno mate. Moment of truth will be when she's all back together!

nice work seb, good repair

Would also love to have a M70 or M90.. but i guess i am stuck with my crown.

I also had bad luck when buying my crown from ebay, sold fully functional, and in perfect condition.. Came with a totaly broken rear and faulty electronics

Greets, Patrick

Thanks Patrick.  Sorry to hear about your Crown. Ebay can be a dangerouse place. My M-70 was sold as faulty and I got it (relatively) cheap; I knew that I was letting myself in for a bit of trouble (Had no idea how much trouble! ) But when somthing is sold as working and it turns up dead, that is plain dishonest! Very unfortunate! Did you send it back?

He can't send it back after all that modding he did!

Ahh of course it was that Crown. Well I suppose the upsideis that Ryux now has the best Crown in existance.  (Sorry Ryux; din't make the connection, brain a little slow today! But Iwas blown away inpressed with the job you did on that machine! )

hehe thanks well yeah, still some work to do, but i think i made the best out of my situation, still i think the JVCs Case would have been better for modding i guess, but i havent seen one in person so far. How is the build quality of your box ?

As Si says; the build quality of the 70 is very good. I don't think it lends itself to modding as much as your Crown does. The advantage the Crown has is lots of internal space to play with. The 70 is faily packed. Probably space to upgrade the speakers though.

ah ok i got you.. so probably i wouldnt have room for the massive speakers i put into the crown on the jvc.

Still i would really love to hear a M70 or M90 for comparison, too bad there is no one around here

You never know what might come along; you maybe lucky some day! Shame we all don't live close together, it would be great to meet up and compare stereo's!

Well that's why we had a meet last year at Doc's house...we all brought boxes and tried them all out...it was fantastic fun and a great way to compare boxes side by side to see what you like. Great way to meet other lunatics too!

Reckon we ought to have another meet

I would love that!

Hi All;

Last Friday a parcel turned up containing two brand new M-70 sliders and a replacement capstan belt. I now have a fully working M-70 chassis. All that remains now is the task of deep cleaning the cabinet, speakers and hopefully source some better trim parts.

The company that sold me the parts is called “4ourhouse”. They are friendly, helpful and efficient. There is a four week lead time on these parts; they probably have to come from Japan Prices are as follows –

£9.75p each for volume sliders

£6.50p for the capstan belts

The web address is – www.4ourhouse.co.uk or you can call them on 08445572510

I am very pleased with this outcome and all going well the M-70 will be booming for Christmas!!

happy to hear that !!! Lets have a Christmas Blast

Cheers Ryux

WTF!?!...they actually supplied the sliders?...WOW, I'm amazed. I got the distinct impression from previous threads they never came up with the goods so I never even tried them! I waited an effing year when I could've got a slider cheaper and in 4 weeks! Feel really stupid now lol

I feel over the moon about this!  Not just the sliders Si but a capstan belt as well! And they may even ship me a rewind, fast forward idler clutch if they can get it, not that the machine needs it but for £6 I thought i would have it as a spare. You are more than welcome to my old sliders if you want to have a crack at fixing them but for £9.75p you don't have the hassle!! (Drop me a line if you want the sliders; I'll send them to you!)

Very good Seb! I'm expecting my sliders this week! Can't wait to fix the M70! It was more than four weeks! I waited more than 7 weeks and think they ordered a batch, so you got them quick  Have fun with the fix, nothing better than mounting NEW parts! 

Sorry Seb was so stunned that you got new sliders I omitted to congratulate you on getting your M70 sorted! Tell you what, if you send me the sliders I'll see if I can fix them without affecting the resistance level too much as I've still got the stuff to do it, then if they're ok I'll offer them up to anyone who needs one and send it for free...you never know how long the new ones will be available and its better than binning them do you reckon?

That sounds like an excellent idea Si; I will try and get them sent to you next week mate

Absolutely mate. I really feel like I'm getting somwhere! Good luck with your fix too

Thanks!