JBE series 3 restoration. Next on the list....

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Ant
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Re: JBE series 3 restoration. Next on the list....

Post by Ant » Wed Sep 13, 2017 5:35 pm

yes d1 is a zener and yes you were right about the connections on the transistor. I took the bloody thing off the board and the pins were marked up on the underside, nothing on the can anywhere other than the part number.........
have i finally got it ? i think the bridge is now a bridge. thanks nick

ImageIs it finally right?!! by anthony cresswell, on Flickr

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Nick
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Re: JBE series 3 restoration. Next on the list....

Post by Nick » Wed Sep 13, 2017 5:41 pm

Yep, that now makes sense.
Resistance isn't futile it's V / I.

Ant
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Re: JBE series 3 restoration. Next on the list....

Post by Ant » Wed Sep 13, 2017 6:20 pm

Thank gawd for that. Eyes on stalks now

Neal
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Re: JBE series 3 restoration. Next on the list....

Post by Neal » Wed Sep 13, 2017 6:56 pm

Ant, did I see somebody mention it is the same motor as the Kenwood KD-550?

If so have a look at the service manual on Vinylengine....it's a bit different......

I have a KD-550 btw and it responds to a better supply like most DD decks

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Ant
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Re: JBE series 3 restoration. Next on the list....

Post by Ant » Wed Sep 13, 2017 8:01 pm

Its a matsushita mkl series motor, the one in this link without the perforated disc bolted to the rotor
http://liquidaudio.com.au/kenwood-kd-50 ... r-service/
I wonder if kenwood changed the motor at some point in production, my motor is dated November 79.
The label has abit missing, it says mkl 15(missing)3
The other difference is the rotor has 8 poles as opposed to 4 in the pic on that website

The plastic cover on the bottom covers the onboard circuit for control of the coils ect

ImageJbe series 3 motor by anthony cresswell, on Flickr

Neal
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Re: JBE series 3 restoration. Next on the list....

Post by Neal » Wed Sep 13, 2017 10:30 pm

It's very wry similar, mine has the optical rotor, is it 18v BTW?

The difference seems to be the rotor....

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Ant
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Re: JBE series 3 restoration. Next on the list....

Post by Ant » Wed Sep 13, 2017 11:02 pm

Yep, the disc and sensor on your kd provide the feedback to the ic on the board attached to the base of the motor, wheras mine has more poles but no feedback loop I can see unless ive missed something somewhere that gives a reference back to the ic.
I think it is 18v, the tx is 20v, but i assume there will be some losses in there, and I did read somewhere that someone was using an 18v supply with one of these that was non standard

Ant
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Re: JBE series 3 restoration. Next on the list....

Post by Ant » Thu Sep 14, 2017 9:34 am

Found the correct motor type, its a matsushita mkl 15b3.
I see no reason why another mkl series motor wouldnt be a drop in replacement as they seem to be 18v, and have the same physical dimensions, and the first iteration of the jbe which were the environmental sound branded ones appear to have had the mkl 15 sit motor which appears to have been pretty common

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Re: JBE series 3 restoration. Next on the list....

Post by Ant » Fri Sep 15, 2017 10:30 am

Ive done a little measuring of the power supply this morning.
With no load the psu outputs 20.1v irrespective of what position the adjust pots are in, and wether 33 or 45 is selected. As you would expect.
Measuring under load with the deck turning its putting 19.6v out at the connetor for the motor. Same again, no change if the pots are twiddled. Interestingly, the voltage aint that stable, it wavers around by around 0.3v. Now this could just be due to the motor being cold, but it got me thinking. I could reasonably assume that the more stable the dc supply is, the more stable the motor speed will be, and that a fluctuation in the supply voltage however minute and short of duration, will cause a speed fluctuation. The heavier the platter, the less this will affect it due to the flywheel effect, but its still a momentary loss of drive.

Last time I was in maplins I saw a vellemann regulated power supply that will do between 1.5 and 35v at 1a, or 1.5a max. It looks like if you put a heatsink on the lm317 this can be increased. It was about 8 quid, and has overcurrent protection on board
https://www.rapidonline.com/Velleman-K1 ... 2AQAvD_BwE
I was looking at these boards at the time to use as heater supplies for small signal valves, specifically the nuvistors in the phono stage.
I wonder if these boards could replace the board I traced in the jbe power supply?
I dont know what current the motor would pull from the psu under load, but i cant see it being that high given the size of the mains transformer.
For less than a tenner does the panel think it's worth worth trying one in place of the original board? Last thing I want to do is fry the motor.....

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Re: JBE series 3 restoration. Next on the list....

Post by Neal » Fri Sep 15, 2017 10:50 am

When I messed about with the PSU on the PL-71 I found a very similar issue Ant, the stock supply is not stable I found it varied (bounced) like you and had a large amount of ripple imposed on it. The deck will respond well to a clean DC supply surprised its ~20v though......I doubt you'll fry the motor but I'd aim for 18v unless you find documentation to say otherwise....a good and simple pre-tracking regulator will get you there for small outlay configured as suggested on Acoustica.org

Edit to say think the draw is 9w at 18v so 500mA. Put a heatsink on that board if you go for it....
Only the Sith deal in absolutes.

Ant
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Re: JBE series 3 restoration. Next on the list....

Post by Ant » Fri Sep 15, 2017 11:30 am

Ta for the current draw info neal, the sticker on the motor is that faded now that none of the relevant info is readable any more......
Its probably that my mains voltage is abit high which has pushed the figures up. Putting the meter on ac shows a varying figure between 0 and 0.3v so there's some ripple there.
The bfy51 datasheet shows max collector current of 1a so thats pretty much in line with the lm317. At the moment im thinking more about a drop in replacement board to be able to recommend to others as a fix for a dead supply. Ive been in conversation via email with a few people recently regarding dead, and non speed stable power supplies, and if this board could replace the original it would be good news for other owners of these decks. Not necessarily an upgrade, but to get knackered ones working again. I have seen lm317 based dc motor control circuits on the net, so it may be worth investigating

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DSJR
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Re: JBE series 3 restoration. Next on the list....

Post by DSJR » Fri Sep 15, 2017 11:48 am

Apologies if I misled about the Matsushita motors - by 1979 I had my Linn chip installed and KJ had all but abandoned anything 'Japanese' at this level by then :roll:

I have some 'Choice reviews on the JBE if anyone would like me to scan them - for no other reason than to give the deck a kind-of 'place' in the history of things...

Ant
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Re: JBE series 3 restoration. Next on the list....

Post by Ant » Fri Sep 15, 2017 12:17 pm

Nope dave, wasnt misleading, it looks like some models of the motor were prone to faliure exactly as you described. Failure of the ic on the control board attached to the motor underneath the plastic cover appears to have been the culprit from what I can gather. And it looks like its a pig to get it off to replace anything. No way I can see other than desoldering the 9 large pins. Chances are, if one did go, it was more economical to just replace the motor than attempt a repair.
It seems that that control board was revised a few times to address the issues. The onboard err.. board made it an all in one cots solution, the buyer just had to provide it with a stable dc supply for it to work, and the 5 leadout wires provided basic connections for power, 33 and 45 rpm switching and speed adjustment. In the case of neals kd, the optical sensor counts the perforations in the disc attached to the rotor top, and matsushita could produce custom versions of the same basic motor to spec for the buyers. Jbe just bought in the standard motor and ran it without an external voltage reference, optoelectric sensors, quartzlock ect. Less to go wrong I suppose. That this one ( and many other mkl motor equipped decks) still work after almost 40 years is pretty good going!

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DSJR
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Re: JBE series 3 restoration. Next on the list....

Post by DSJR » Fri Sep 15, 2017 5:29 pm

OK. I must admit to not knowing Matsushita made opto speed checking, as I thought it was all magnetic. I do know I think that a pukka very heavy duty pro motor was made for record cutting lathes, but nothing else about it.

Ant
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Re: JBE series 3 restoration. Next on the list....

Post by Ant » Wed Sep 20, 2017 3:00 pm

got some more done on the jbe, made some new legs

ImageJbe series 3 legs complete by anthony cresswell, on Flickr

The spikes are level adjustable, and the black part is essentially a spacer to get enough height for arm cables to clear if they have a straight din plug.

ImageJbe series 3 legs complete by anthony cresswell, on Flickr

The black part is a piece of turned walnut that the spikes are mounted on, this in turn is screwed on from the top using my very favourite audiophile capped screws.

The caps are pretty close to the original mountings in looks to try to keep the stock'ish' looks. I sprayed the spacer/mountings black so as to kind of keep the legs in line with how it would have looked originally in terms of colour. basically black and aluminium. I think the legs fit in visually quite well with the overall look

starting to get there now

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