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  #1  
Old 05-19-2017, 07:33 AM
hipacky hipacky is offline
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Frustrated Dragon Power Supply Problem - Please help!

Hi all,

So, my Dragon started acting up yeterday and I found that the Auto Azimuth belt had to be replaced. Replacing the belt wasnt too hard, but after I had the unit back together, I plugged it in and... nothing. The counter lights up and thats all.

So I started investigating if I accidentally disconnected something... and I noticed that I smashed pin 1 of CN-34 a against the chassis, causing a short! Oh no...

I obviously fixed the short, but +12V on CN-34 and -12V on CN-10 are dead.
I measured resistance on the +12V pin of CN-34 and it shows a 70 Ohms resistance to ground, which I also think is too low. Not sure what is causing this.

I tested Q402 and it measures fine. Im not very familiar with the Dragon electronics so I have no idea what to look for and where. All I know is that this accidental short made something fail. Fuses are OK.

Im so sad right now, what was a simple belt change now made my Dragon an expensive paperweight!

I appreciate any input.
  #2  
Old 05-19-2017, 04:16 PM
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Open fuse? That is what should happen with an accidental short. Each secondary of the power transformer has its own fuse.
  #3  
Old 05-19-2017, 04:53 PM
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390FE 390FE is offline
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Like Nakdoc said. (see below pics)

100_5979.jpg 100_5980.jpg

You will see the original Fuses are pigtails & soldered in.


I suggest you convert them all to clip in fuse holders like I did. See below.

100_5981.jpg

100_5983.jpg

100_6017.jpg


Note: I did not damage or modify the original board that can be seen. I only had to slightly open the solder holes in the board so the clips could be inserted flush with the board (like a factory job) & soldered in. My fuses were not blown so all I did was fold the pigtails under the fuses & clipped the fuses into the holders.

Note #2: I did NOT need cut the cable ties or unsolder any wires from the Fuse Board to remove the original Fuses & drill a little bigger holes to solder in the Fuse Clips.


Hope this helps.

Last edited by 390FE; 05-19-2017 at 04:56 PM.
  #4  
Old 05-19-2017, 08:04 PM
hipacky hipacky is offline
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Hi guys, thanks for replying.

Fuses were OK, they did not open, not sure why! I guess current never rose high enough and something blew first.

I spent the afternoon reading the schematics and figured some transistor should be bad. After some testing, found Q403 defective, that was the problem.

OK, so now I have it working again but have another question: I noticed one of my level adjustment trimpots to be 'noisy'. After taking it apart, I found it is actually broken. Where am I gonna find a replcament for this? Any ideas?
  #5  
Old 05-19-2017, 08:46 PM
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390FE 390FE is offline
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Can you post some clear pics of it along with it's ohm value?
  #6  
Old 05-20-2017, 02:24 PM
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The controls usually show up as a unit on ebay, and they sell for a lot. I would post a request here, and maybe you'll discover someone with one to spare.
  #7  
Old 05-21-2017, 07:47 AM
hipacky hipacky is offline
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I have a attached a pic so everyone knows what Im talking about.

If they run for a lot, that probably means this things break often, as many need them. I didnt even know mine was broken and to be honest I never pushed it hard or anything that could explain the damage. I guess they are not very sturdy. I guess I'll just have to find a fix without replacing it...
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File Type: jpg Foto 20-05-17 08 46 37.jpg (62.0 KB, 58 views)
  #8  
Old 06-30-2017, 03:43 PM
gvwrighty gvwrighty is offline
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You should be able to repair this.

I had a few noisy pots and replaced them. Luckily I had similar ones, but from the photo it looks like it is VR104, a 50k pot, which you should be able to find an equivalent for. If you can find the brand name on the pot that may help.

Take a look on Mouser, you may be aable to find something that works.

Alternatively, Nakamichi list the part as 0B07277A. Take a look at the circuit diagrams for other, less sought after Nakamichis as you may find they use the same pots.
  #9  
Old 07-03-2017, 01:46 PM
hipacky hipacky is offline
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Quote:
Originally Posted by gvwrighty View Post
You should be able to repair this.

I had a few noisy pots and replaced them. Luckily I had similar ones, but from the photo it looks like it is VR104, a 50k pot, which you should be able to find an equivalent for. If you can find the brand name on the pot that may help.

Take a look on Mouser, you may be aable to find something that works.

Alternatively, Nakamichi list the part as 0B07277A. Take a look at the circuit diagrams for other, less sought after Nakamichis as you may find they use the same pots.
Those are ALPS pots, but they look like a custom made pot for Nakamichi, as I cant even find pics of these over the internet. I know basically any pot will do, but I want something that fits the same space and also one that takes the original Knobs, or at least something that could be somehow modified to fit and keep the original look and functionality.

It didint occur to me to look for other parts deck with the same part number, good idea
  #10  
Old 07-03-2017, 05:23 PM
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I have seen similar pots with the splined plastic shaft. Though they may have a longer shaft (easily fixed by cutting it down as needed). Though sadly at the moment I don't recall where. It may have been replacement parts or in another make/model unit. Ah I now remember one location I have seen similar pots, in old TVs for the rear panel adjustments and sometimes on the front. Though thse were usually right angle pcb mounts vs the straight ones as used on the Dragon.

2 things.

1) Have you tried to clean the pot in question with some DeOxit F5?

2) IF 1 above solves your problem with the noisy pot, it looks like you could reattach the plastic shaft using RTV/Silicone, super glue or epoxy. Provided you still have that part/pieces. I suggested the RTV/Silicon as it can be undone/removed if needed and done right will be strong enough to hold it.



.

Last edited by 390FE; 07-03-2017 at 09:54 PM. Reason: spelling typo.
  #11  
Old 07-04-2017, 05:03 PM
hipacky hipacky is offline
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Quote:
Originally Posted by 390FE View Post
I have seen similar pots with the splined plastic shaft. Though they may have a longer shaft (easily fixed by cutting it down as needed). Though sadly at the moment I don't recall where. It may have been replacement parts or in another make/model unit. Ah I now remember one location I have seen similar pots, in old TVs for the rear panel adjustments and sometimes on the front. Though thse were usually right angle pcb mounts vs the straight ones as used on the Dragon.

2 things.

1) Have you tried to clean the pot in question with some DeOxit F5?

2) IF 1 above solves your problem with the noisy pot, it looks like you could reattach the plastic shaft using RTV/Silicone, super glue or epoxy. Provided you still have that part/pieces. I suggested the RTV/Silicon as it can be undone/removed if needed and done right will be strong enough to hold it.



.
Yes, I did try spraying DeOxit at first, but then, on a closer look, I noticed they were actually broken. Looks like someone hit the knobs too hard on the front and that broke the pots underneath
  #12  
Old 07-05-2017, 10:16 PM
gvwrighty gvwrighty is offline
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This might be a possible.

http://www.mouser.com/ProductDetail/...Gra4sCu3bvo%3d

You'd need to check into the sizing, but I made some replacement 3D printable knobs for a deck that had missing knobs.

https://www.shapeways.com/product/FR...ionId=61500588

If the pot above can be drilled and fitted onto the board and there is enough clearance to the hole in the facia, it would be possible to create a 3D design so that a knob can be printed to fit this pot.
  #13  
Old 07-06-2017, 06:43 PM
hipacky hipacky is offline
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Quote:
Originally Posted by gvwrighty View Post
This might be a possible.

http://www.mouser.com/ProductDetail/...Gra4sCu3bvo%3d

You'd need to check into the sizing, but I made some replacement 3D printable knobs for a deck that had missing knobs.

https://www.shapeways.com/product/FR...ionId=61500588

If the pot above can be drilled and fitted onto the board and there is enough clearance to the hole in the facia, it would be possible to create a 3D design so that a knob can be printed to fit this pot.
First of all, I must congratulate you for taking the time to print those Knobs and make them available for all of us who still use and cherish our tape decks. I know this means a lot of time, work and effort that might not necessarily bring you any money as demand is low, but I know you did it to help all of us who are desperate for a solution for missing parts. I do not need them now but please keep them available for us, it will certainly come in VERY handy when someone needs those.

As for the pots, the pinout on that one is pretty different. They might fit with some modifications, but not perfectly. I plan on going to a store in my area that sells parts from dismantled electronics. I obviously wont find a Dragon board there, but I may find similar pots from a TV set or something else as you suggested
  #14  
Old 07-07-2017, 09:11 AM
gvwrighty gvwrighty is offline
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I make no money out of the knobs. I made them for myself, then made the design available for others to print if they want them. Someone actually printed a set of red ones!

I was simply suggesting a way for you to solve the problem if you cannot source a board or a pot. You could mod the board to fit this pot, and you could 3D print a knob to fit it, it is not that hard to do and although there is a difference between the look of the knobs, you cannot really tell unless you are looking - and if you cared that much you could print off a set so that they are all the same.

If you did do this, I would hope you'd publish the 3D print and the pot number and make this knowledge available to everyone else like I have.

Best of luck with whatever approach you take.

Last edited by gvwrighty; 07-07-2017 at 09:13 AM.
  #15  
Old 07-09-2017, 09:36 AM
hipacky hipacky is offline
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Quote:
Originally Posted by gvwrighty View Post
I make no money out of the knobs. I made them for myself, then made the design available for others to print if they want them. Someone actually printed a set of red ones!

I was simply suggesting a way for you to solve the problem if you cannot source a board or a pot. You could mod the board to fit this pot, and you could 3D print a knob to fit it, it is not that hard to do and although there is a difference between the look of the knobs, you cannot really tell unless you are looking - and if you cared that much you could print off a set so that they are all the same.

If you did do this, I would hope you'd publish the 3D print and the pot number and make this knowledge available to everyone else like I have.

Best of luck with whatever approach you take.
I'm not familiar with 3D printing and have no idea what software to use. What did you use?

I'm trying to source some pots taht could at least fit the board, and then I would consider printing knobs to fit these replacements. My goal is to make fez mods to make a current production pot fit there.

Of course I will make my findings available, I always do that to every thread I post here. Everyone here has always been very helpful.
  #16  
Old 07-09-2017, 03:30 PM
gvwrighty gvwrighty is offline
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I use Sketchup, then print the design via Shapeways. You just upload your design to Shapeways, they print and post it to you.

Those Bias and Cal knobs cost around $4 each to be printed.
  #17  
Old 07-09-2017, 05:58 PM
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390FE 390FE is offline
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When you go to that shop looking for used pots (like from an old TV or electronics like I said earlier) IF you can't find the same ohm value pot look for one with a higher ohm value. This will give it a wider range though may not be noticeable in your calibrations BUT it WON'T limit it like a lower ohm value pot will & that would be noticeable when a near the limit tape would not cal after with the lower range pot.

Also expand your search to other makes of pots like Bourns & others (my brain isn't booting up right now & can't acess any of my memory files of other makers at the moment. lol).


.

Last edited by 390FE; 07-09-2017 at 06:00 PM.
  #18  
Old 07-14-2017, 10:50 AM
gvwrighty gvwrighty is offline
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Have you seen this on ebay?
http://www.ebay.com/itm/NAKAMICHI-DR...-/302375791356

At $66 it is expensive for 1 POT, but perhaps you can part the rest out.
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