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my National RX-7200 88-108 MHz FM and 120VAC modifications/repairs


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#1 toshik

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Posted 05 April 2015 - 10:49 AM

What can I say? It's an amazing one, great design and sound, especially comparing to my childhood tiny RQ-4050FD...
Both original 76-90 Mhz and 100 VAC are quite disappointing.
FM due to the fact that it only picks 2-3 stations from the bottom of the US band around 88-90 Mhz.
100 VAC is simply a disaster area - RX-7200 is made to work off 12-15 Volts DC as noted on the back.
When plugged into Florida's 120 VAC outlet (outputting about 125V) the internal transformer outputs 17.5 VAC as a result!
After the rectifier bridge is sends pretty much fatal 22.5(!!!) Volts DC to the main board which would kill the 33-years old beauty quite fast. It can run off DC adapter, but most of recent adapters are switch mode not linear, so they would cause extra interference plus it's large external non-OEM piece.
I took care of both issues so now it has full coverage on 88-108 Mhz with correctly displayed frequency and normal power voltage. What else can be done? Full re-belting is done, pinch roller replacement is pending roller arrival.
Dead indicators lamp might be replaced with the warm white LEDs tomorrow but this is mostly cosmetics.
Will replace power filter cap alone with a few dry ones in but I'm against the total recapping.

BTW is someone needs FM conversion or 120-220 VAC power PM me - there is no need to ship the whole boat, just a few blocks.

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#2 fromNKLwithlove

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Posted 05 April 2015 - 11:30 AM

Wow, nice job!!!

 

RX-7200 is so cool..



#3 oldskool69

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Posted 05 April 2015 - 04:45 PM

Super nice work!  Can you give some details?  This would be a great asset for those who have Japanese spec boomers. :-D



#4 toshik

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Posted 05 April 2015 - 05:09 PM

Thank you! What kind of details you'd like to see?

The work is more complex than rebelting or plain replacement of all electrolytic capacitors, so I'd refrain from step-by-step guide since the results might be quite disappointing due many factors. Not to mention that it might even not being possible for another models. Even this one was a "die hard" :-) due to schematics absence. I've been doing these mods for over 10 years now mostly on car radios. Plus I worked in consumer electronics repairs since early 90-s. 

As I noted above all RX-7200 owners can PM me so I can help them out while I have time and parts.



#5 AE_Stereo

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Posted 06 April 2015 - 09:33 AM

Best of Panasonic classics.

It is amazing that the display had 3rd digit for 100+, though it was mostly a Japan only model, if I am not wrong!



#6 blu_fuz

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Posted 06 April 2015 - 09:37 AM

Nice work getting it switched. Curious to know how you got the FM range to change....?



#7 toshik

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Posted 06 April 2015 - 10:09 AM

100% Japan model the only reason they have the first "1" is because of AM indication. 

It was made before 1990-s when decontenting and penny-saving policy started.

It took a couple of days to figure that out :-)

In a good company alone with RQ-4050FD - 1.5 months of collecting.

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#8 Mystic Traveller

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Posted 06 April 2015 - 02:59 PM

Well done - especially having the tuner "re-tuned".  :thumbsup:



#9 toshik

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Posted 06 April 2015 - 07:40 PM

Speaking of warm white LEDs strip - I gave it a try tonight and I don't like the results...

3-LED strip is about 2" long and there is simply no space to conviniently lay it out against the edge of light carrying acrylic sheet where the OEM lamp was. Also since the LED consumes only 3.5 mA off the 9V light supply when the switch is turned off it dims VERY slowly - must be a cap somewhere in the circuitry.

I think I'll go authentic filament lamp. It only consumes 35 mA off 12 V source. 



#10 AE_Stereo

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Posted 07 April 2015 - 08:56 AM

You can cut the strips into individual chips and recreate the circuit with wires soldered.

I didn't have the problem of slow dimming on my RX-7000. It works just like filament lamp or even better, if not infinitely better :-) .

Pl. see the thread: https://boomboxery.c...ted/?hl=rx-7000

 



#11 toshik

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Posted 07 April 2015 - 11:21 AM

I can only fit one LED into the space ao I'd have to come up with new current limiting resistor. 7000 circuitry might be different without cap need to look at service manual.

#12 toshik

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Posted 07 April 2015 - 05:30 PM

Ok tonight I made it absolutely perfect - took the display to a full extend!
I added the hundredth (.X0/.X5) Megahertz display segment so we have a fully-blown display so tuning makes sense now (you know the exact frequency you tune into).
Not practical in the US where we use only odd frequencies, but correct indication alone with being very very sweet looking :-)

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#13 redbenjoe

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Posted 07 April 2015 - 06:44 PM

thats a terrific piece of work to improve a great box  :thumbsup:  :drool:  :drool:



#14 Superduper

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Posted 07 April 2015 - 06:51 PM

I agree, certainly my most favored box by far. With retuned tuner, it'll be a forever keeper.



#15 toshik

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Posted 08 April 2015 - 02:23 PM

I have people PM-ing me about who made this mod - it was done by me, no external resources or people were involved.



#16 toshik

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Posted 11 April 2015 - 05:18 PM

Sweet - with full FM and 120 VAC!

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#17 Superduper

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Posted 12 April 2015 - 08:28 AM

how come that last digit is dimmer than the rest?



#18 toshik

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Posted 12 April 2015 - 12:19 PM

We have snake eyes in the club :-)

Fixed!

I also noted that the power transformer runs 24/7 even though they use a mechanical switch for power.

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#19 toshik

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Posted 19 April 2015 - 06:46 PM

I never showed the new transformer :-)

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#20 Superduper

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Posted 19 April 2015 - 07:35 PM

That looks like the old transformer.



#21 Superduper

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Posted 19 April 2015 - 07:48 PM

Hey. to you guys that are lucky enough to own an RX-7200, and wish to have your tuner FM band range adjusted to 88-108, I just want to say that Toshik has just recalibrated my tuner for me.  I had a different solution in mind but this was far far easier.  Just pop out the tuner and the FLD display, send it to him, and he will convert it for you.  I found a few moments to install it today and it works properly.  The only thing I forgot about is that stupid japanese AM section which tunes in 9khz increment steps instead of the 10khz steps that is everywhere else in the world.  Not that this matters with an analog tuner but on a digital tuner, it does since you don't have an infinite range to choose from, only increment steps but this isn't Toshiks fault, that's just the way the tuner is/was designed..  However, the FM now works exactly like it is supposed to.   Price for the update is, well that's between you and him.  However, for me, my time is better spent nowadays on my other more pressing priorities right now, and I was happy to let someone else do the work for me.  Heck, I don't even have time to open up and dust my machines much less do rebeltings...  just no time.  Just wanted to say that if you want it done, he can do it.



#22 toshik

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Posted 19 April 2015 - 07:50 PM

Thank you!
Just the metal shell is original - original transformer has only 2 leads in and 2 out and they are in a different colors.
Transformer is new, I like everything perfect even inside where nobody can see it.

#23 Superduper

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Posted 19 April 2015 - 08:19 PM

Just the metal shell -  original one has only 2 leads in and 2 out and they are in a different colors.

Transformer is new, I like everything perfect even inside where nobody can see it.

Yes, I did see that it looks a bit different, in the windings section.  But I just presumed that it was a variation on the components the manufacturer used.  Looks a bit like a stanton?

 

On mine, I replaced it with Radio Shack 273-1511.  It was 12.6v @3amps.  Did the math and basically looks like perfect replacement.  The mounting orientation of the shell bracket is different though so the only way to retain the original mounting would be to swap the shell like you did.  With the radio shack shell, it would mount normal instead of diagonal which it seems would put less stress on the rear case as it would not hang as far out, and therefore, less leverage.  But I am guessing the unorthodox mounting orientation may have to do with reducing noise since the windings on the orig transformer had unshielded windings.  The good thing about the Radio Shack transformer is that it's fully shielded, even around the windings so that should not (and has not been) an issue.  I decided that loosening the shell and maybe introducing a mechanical hum in the process, as well as losing the winding shields was not worth it to look perfect untouched.  To me, having the shell say 100V when it's now a 120v transformer leads to confusion for future techs.  Before swap was just tad under 23v.  With RS transformer, now getting about 19.5V after the full wave rectifier with no load.  That seems about in line with other 15V boxes on AC and no load (unregulated supply).



#24 toshik

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Posted 19 April 2015 - 08:30 PM

Nothing to worry - there are clear voltage markings on the new transformer coil. Original transformer is not shielded. Radioshack transformer is NLA, it's only 120 VAC and I'm sure it's the same OEM China brand I used.

#25 Superduper

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Posted 19 April 2015 - 09:23 PM

Nothing to worry - there are clear voltage markings on the new transformer coil. Original transformer is not shielded. Radioshack transformer is NLA, it's only 120 VAC and I'm sure it's the same OEM China brand I used.

yes, I wanted 120 VAC.  Radioshack is of course going out of business but I found 3 at one store and snapped them all up since it's a common size used on boomboxes.  You can still get them on eBay. 



#26 toshik

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Posted 22 April 2015 - 10:28 AM

Just more pics :-)

And his little brother (just plain restoration and clean-up)

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#27 AE_Stereo

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Posted 23 April 2015 - 09:15 AM

We have snake eyes in the club :-)

Fixed!

I also noted that the power transformer runs 24/7 even though they use a mechanical switch for power.

 

You are a master electronic expert!

 

I have seen that many Akai "upside downers" have the AC power light "on" whenever it is plugged in. Even when the Power switch is off, indicating that AC power is on.

May be because they wanted to fix the power switch on the board, which is at DC level.



#28 toshik

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Posted 27 April 2015 - 09:15 AM

Thank you!



#29 toshik

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Posted 08 June 2015 - 05:23 PM

Up as reminder to all proud RX-7200 owners see what you are missing and there is no need to send the whole box over to me for the mod :-)
Based on my experience with the model I can also fix dead cassette channel (very common problem) etc.

#30 toshik

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Posted 10 June 2015 - 11:31 AM

More pics

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