This M90 was displaying a continual clicking, like the initial reset it does when first powered on without a tape in it. So what to do and where to begin ?

Well, first off in order to check voltages correctly, we need to use the DC input which was not working. I took the board out and did a few checks and noticed a faulty resistor pretty quickly so replaced it. I also noticed that the piece of metal inside the DC connector was bent flat so was not making too good a contact with the adapter. Bent out this a little to get some traction on the adapter and DC was back up and running.

This was an important first step in order to be able to troubleshoot further.

I noticed that when the deck was clicking it was pulling the solenoid in and releasing it as part of the cycle. I also noticed that the flywheel was turning continuously so it was almost as though the deck believed it was in play mode even though the heads were not raised. I decided to clean up the solenoid first off and just make sure that was operating as it should. I checked the diode on the solenoid too by taking it out of circuit. The diode was good, as was the solenoid.

At this point I'm doing some voltage checks, now, it is important to note that there are some errors on the JVC M90 schematic, namely, there are numerous components listed twice and some pointing in the wrong place for resistors that were printed into the board. This meant I spent time on following traces on the board to be sure I was checking the correct components etc.

From doing initial checks I noticed quickly that fusible resistors FR704 and FR703 were toast because voltage checking on the feed side resulted in a large voltage drop being fed to the 12v Regulator (Q712). Once those were replaced I confirmed that the 12v rail was indeed now regulating to 12v. The continuous clicking was still there at this point.

Continued with checking and focused on the 7v regulator (I did this because I noticed that the 7v regulator was not, well, getting 7v output but was seeing 14v!) and noticed that a diode was checking out weird while in circuit. At this point I went about checking every single diode in the board first to establish any pattern to the testing to try and save time in taking diodes out the board but I noticed that diodes related to the voltage regulators looked bad in circuit. I wasn't happy with my results so decided to spend an hour taking each diode out of the board one at a time and checking them. This proved worthwhile as I found 2 were indeed faulty. 1 diode (D701) is related to the 7v regulator (Q701) and another diode (D705) is related to the switch which recognises a cassette is in the mechanism. This meant two things, the 7v regulator should now be being regulated to 7v properly and the deck should now sense when a cassette is in the deck. Oddly the latter was true but I still was not getting the correct voltages via Q701 the 7v regulator. I quickly established at this point that another fusible resistor (FR701) was toast.

Now, replacing D701 and FR701 was a mission since some of the circuit board there was damaged (I think it might have been caused by damp) and had lost the contacts on the board. I had to bridge the fusible resistor which connected to the collector of Q701 which was vital. That done I had to scratch a little board away to reveal the copper where D701 went to Q701 Base. I soldered D701 to it and did voltage checks which now looked good!

Incidentally I also took around 4 or 5 transistors out of circuit since they seemed bad when testing them but out of circuit they were all good.

At this point I was spending a lot of time checking things over and the deck had stopped continually clicking! I felt as though I was finally getting somewhere! If I put a cassette in it would automatically try and play but something wasn't quite right. I replaced the belts and lo and behold, when putting a tape in the deck it automatically played, not right but it was playing !!!

At this stage I called Chris and he didn't hesitate to offer help to check the deck for mechanical issues. Chris picked it up, took it away and recognised a fault with the main gear which he was able to fix! We were making good progress! I'm not sure what the problem was but Chris was able to be sure that it was now mechanically sound.

After Chris dropped it off again I set about doing more checks.

The deck at this point was automatically playing tapes. None of the buttons operated but pressing stop did stop the deck then it auto played immediately when I released the stop button.

I was going round in circles at this point and then realised that D701 was fried again and so was D703 which is also part of the 7v regulator. It is important to note that when doing checks on this deck it is really easy to fry some component and that is exactly what happened here. I replaced these and was now seeing correct voltages again but the unwanted auto play feature was still occurring...

I turned my attention to the chips, not the potato kind either. I found a problem with the help of another member, IC701 pin 5 and IC706 pin 8 are connected to one another and deal with the tape play and Timer/Standby function since pin 8 of IC706 is a gate and when play is pressed it makes the deck play (doh!). What I found was that there were zero volts here which seemed to indicate to me that it was causing the instant play mode as when playing I expect there to be very low voltage here as indicated by the schematic.

I desoldered pin 8 of IC706 which relates to the Timer/Standby function and made sure the pin was out of circuit by doing a continuity test on the pad of pin 8 and pin 8 itself. At this point a voltage check showed 5v at each location, I put a cassette in and it no longer auto played it! Pressing play it played! pressing stop it stopped! I've a feeling that IC706 is toast which is bad news since they are unavailable anywhere (I believe it is bad because I checked the entire Timer/Standby circuit of Q707 and it appeared to be good). However, it only seems to be a problem with the Timer/Standby function so I left it desoldered.

The deck was now responding as it should with the exception of FF/REW. I did a few more checks but was starting to flag at this point and again wondered if the problem was mechanically related so called Chris again and he came to pick it up for another inspection.

Chris was able to establish that the deck was mechanically sound and he also noticed that the voltages provided to the Reel motor did not seem to be high enough. The reel motor is fed from IC702 on the 7v rail but it was only receiving 5v and outputting 3.odd volt to the reel motor. We did a quick check of the IC datasheet online and found that it can operate at up to 15v. We also checked the service manual and found it should be 7v when the FF or REW is pressed and 0v normally. Chris tested a 7v supply to IC702 and low and behold the FF/REW buttons were now working. Meaning we had touchdown ! the deck is fully working with the exception of the Timer/Standby feature.

That is as much as I can remember and I am certain I have missed elements of my testing and findings over the course of the 20-30 hours I've spent on it. I'm sure I also probably missed parts that Chris did but this has gone on over the course of weeks or months even, so apologies for that.

Chris is a gem and will be getting it back to me soon. I'll give it a once over service wise and this one is finished.

Jeezus! you guys weren't kidding or exaggerating when you said what a bitch of a job this was to sort, a real headache indeed!  well done both of you and thanks for sharing docs!

good on you

Sounds like a nightmare so well done!  Thanks for sharing the fault finding.

that's what i call a labor of love. great stuff, not to be seen every day!

one word.................genius

yeah that was well described,

Dave...I got to say the troubleshooting is extrodinary!!!  Fantastically detailed to boot!!

Make this post a sticky!

Both Chris and Dave are a credit to the fine hobby! I just wish you two would drop over to Canada ...we'd keep you gents busy. Your skills are are hard to come by here

EXTRORDINERY....AND OUTSTANDING how come this thread has only just shown up for me....now some of it makes sence as to what you guys were telling me over pm

your wright dave some of the damage was caused by damp.....the guy i bought her from said she had been locked away in a garage for 20 years,,,this is the mirilcle of the year for me and the m90,,,,not meaning to sound rude but i think this repair must have pushed you harder than any other box

one wonders how there were so many faults just sitting in a garage....he did say he had tried to have her repaired,,,the only reason he said he sold it me is beause i had fixed so many and had parts....he said those stikers all 100 had special meaning...whish i had asked him the meaning of them,,,,i kinda wish i had left them on...there is only 1 on there now....it must have taken me 24 hrs just to remove them....

anyway outstansing work guys,,,,seriously i doubt a so alled prefesional of the trade would have attemted this repair,,,,outstanding and nice to have a glimpse into eletctronics   an art of the past

^wow Dave thats some right up, i know you guys struggled with it through talking to Chris..i wish i had yours and Chris`s knowledge and expertise with repairs.

Unreal. Cris and Dave are true Masters. This all seems like space shuttle kind of stuff to me. Just reading how technically advanced these units were for their time is mind boggling. I wish there were more technitians like this around. Dave and Chris should start a school.

Just wondering- Are todays electronics more or less complicated to work on? Are modern electronics non serviceable? I know a vehicle mechanic that loves when I bring in my old Ford Bronco because they are used to the more modern complicated vehicles, and they say "oh good something old and easy" - screwdriver, 1/2 wrench and a timimg light, and can just about tune it up. Are the older electronics like this for a modern tech.? Do they look at them and kind of giggle and think - Dinosaur - this aint nothin?

Eddie thanks for your comments but I am a total newbie when it comes to electronics, I just have a capacity to keep trying I think the electronics phenomena is the same old and new but newer stuff tends to be smaller and components more intricate than before. So diodes and resistors etc tend to be a whole lot smaller than before and by and large I think it depends on the type of device and the function it serves. But I think the principles remain the same, there are specific types of circuits that are more efficient for a specific type of purpose which was true then and I think is still true now.

docs, Thank you for the reply and explanation. I am sure alot depends on parts availability, or having to manufacture a broken part or finding a part from another box that is compatible even if different manufacturer. It seems your best bet is to try and source a second box just for spares. Can be expensive, but alot of boxes are sold as is or not fully working that can still be a great parts source. Example: I would try to score a basket case M-70 (as long as price is ok ) just for all those parts if needed.

For the record and for full transparency, the facts above are exactly that, over 30 hours of work and head scratching to fix numerous faults. This deck was working when shipped with the exception of the Timer/Standby feature because of the likelihood that the IC was faulty and irreplacable without buying a spares box as Eddie mentions above.

The remit of the fix was around the deck functionality. There have been previous members looked at this and been unable to remedy the continual clicking problem as can be found in a previous thread going back some years.

Since returning it, another fault was highlighted whereby turning the volume up over half way (which on an M90 is not always necessary) the cassette mechanism would stop. I was not made aware of this problem until AFTER it had been returned and I'm not in the habbit of running M90's at silly volumes to check if the deck would stop as a result.

The work that both Chris and I undertook remedied the deck situation. The fact that there was another fault previously unidentified meant that the owner took upon himself to open the unit (which I should have glued shut) and start messing around with the deck. The result is this thread.

The further fact of the matter is that Chris paid for the M90 returning. This cost just under £20. This was in order to secure the sending of a box which Chris needs parts from to raise another one he has from the dead and was continually promised as a gesture of good will for putting in hours on the M90 deck.

Furthermore, Chris will not be receiving anything and least of all a response to PM's regarding the above.

It takes 2 seconds to burn a bridge and 20 years to rebuild it. I am saddened that members find it enthralling to fuel a fire which is clearly deadly, especially when it serves no other purpose than to attempt to tarnish good member's reputations and kind gestures of help in an otherwise hopeless situation. It really does beggar belief.

I have presented the forum with the facts above as a statement of this farcical situation. There are some that will continue to fuel the fire and be attracted as people are to "victims" and "casualties" but when you realise the damage you are causing by doing so, PM me and maybe one day we can become boombox collecting brothers once more.

One more thing, Sal I appreciate your comments moreso now than ever.

I diddn't read this thread....It is no ones fault this has happened but belive it or not Docs i have fixed more of these m90's than you will ever see,,,,deliverance is still welome to his box if he wants it,,,,,,but it is no ones fault especially docs or deliverances....i am deeply saddened by this whole frigging mess as much as anyone....these boxes are old such is life....but once i send deliverance his box paying you docs and deliverane leaves me hugley out of pocket....and im not sure why i should HAVE the blaime for this eather.......i didn't dream of this situation in my wildest dreams

http://REPLACEMENT ERROR/topic...4#362147801689155354

and that thread wasnt posted for any bad reason i was simply going to sell the m90 as its usless to me with out a deck

so have i EVER blaimed you dave or chris NO if you think i have then you need to learn to read my friend

i am fuilling no fire i just wanted a working m90...or to sell it as its usless without a deck...end of story

DITTO^^^^^^^^^^^^^^^^^^^^

@Reno  I feel your pain brother but a little advice if I may?  Keep the box. It CAN be fixed. A crapload of labour and troubleshooting went in to this and when all is said and done, and the 90's functioning %100 again....you'll kick yourself for wanting to unload this in a hurry. Patience my friend..

Anouther Ditto from me. The world needs people like deliverence and docs, they who are prepared to go the extra mile.

Reno mate; as Brutus says, don't give up on the box. We all have a runs of bad luck from time to time but they don't last forever.

Wow guys supreme dedication there, impressive stuff. Im a newbie here but it seems like a real dedicated community, good on you all.

it was the man in the moon

DITTO

Well guys the m90 will not be sold after so much work has gone into her by two pro's which i am Very gratful for....

and one other bit of news...The deck is now fully working...so can we please put this behind us.....the last thing i EVER wanted to do was give anybody a bad rep or offend Docs or Deliverance....peace

That is fantastic news Reno, along with many others I am delighted that everything is now sweet.

You should now make arrangements to get the JVC box that you promised to Chris sent without further delay. It's not worth whining that you don't have the money to pay for the courier; after all Chris paid the courier to get your M90 back to you and you can find funds to buy new machines like the Goldstar you got from Germany the other week. Make this a high priority and let's put all of this behind us because I for one have had enough of hearing about broken promises lately. It's the worst kind of deceit, made especially painful when others do so much for you.

That is how you arrive at 'Peace'.

Nick my name isn't lav loo...i get paid Next week on thursday and i shall make arangments then....it's gunna cost far more than £20 for me to send ...not that i mind..royal mail sammers...i have also asked deliverance for his adress which im still waiting for...other than that it will be good to go next week my man.....and thanks for the congrats im over the moon well sorta.....this has been quite a drama which i diddn't intend...cheerz mate

Reno, I can't be the only one here who wants to know how you got the deck working again, can I?

...do tell  

Years of dedication to the 90 i guess paul

Ok i'll spill the beans...as i thought a few fusible resistors had blown as the deck was displaying no signs of life just a simple little click which i guessed was the solenoid trying to activate but no clunks nothing....which suggested to me fusible resistors  had blown....i took her apart for one last look and could spot nothing obvious....anyway i decided to put my glasses on...couldn't see anything wrong...then looked at the last place i could think of....the motor...everything seemed fine then i took a closer look...one of the motor wires was hanging on by a thread....soldered it back on properly and bingo the deck sprung to life...there ya go lad

Everybody loves a happy ending  

Well done Reno!

Great to hear she's alive.

Now keep your glasses on...go out to your shed and see if there's a minty SK-95 for me in there.