Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 Next   Go Down
  Print  
Author Topic: Bad regulator in FT-101E  (Read 8371 times)
KD5FPO
Member

Posts: 28




Ignore
« on: January 29, 2011, 12:11:46 PM »

I have an early Yaesu FT-101E with the 1314A regulator / calibrator board. The MFC-6034A IC got zapped and died a quick death. These little buggers are next to impossible to find. Does anyone have a proven simple modification for this board to get it back on its feet again? Any ideas or help will be greatly appreciated. 73 and good DX. Mike KD5FPO@juno.com
Logged
KE3WD
Member

Posts: 5689




Ignore
« Reply #1 on: January 29, 2011, 03:35:57 PM »

The IC may indeed be unobtanium, but that is because today we have a better way to get the required regulated 6V for that circuit. 

Use a 7806 three-terminal regulator along with three capacitors and a heatsink.   

A rather large "tank" electrolytic across the input to pin 1, which can be anything you have from maybe around the 10uF ranging up to 100 or 220uF should work. 

A 0.01uF across that electrolytic, close to pin 1 of the regulator. 

Another 0.01uF across the pin 3 output. 

Take a look at this online schematic and just ignore the bridge and everything before it, what you want for your '101 are the components surrounding the 7806 regulator. 

http://www.circuitstoday.com/6-volt-regulator-circuit-using-7806


Here is how I've repaired a few 101's with the same problem.

Remove the original IC chip from the board. 

Find a place to mount the heatsink and the 7808.  This can be on the board or even offboard, using a piece of the metal chassis for your heatsink.

Examine the schematic of the regulator section of PB-1314 and note that the remaining components can be left in place and become the filtering capacitors for input and output of the new regulator. 

Run an insulated wire from Pin 2 of the removed IC over to pin 1 of the 7606, this will bring about 12VDC for the input.

Run another insulated wire from Pin 4 of the removed IC footprint over to pin 3, the output of the 7808. 

Center terminal of 7808 goes to chassis ground point on the circuit board, the negatibe side of C13 of C16 is a good place to find it. 

Tack a 0.01 disk  across C13 and another across C16. 

Done. 

Years ago I tried using a much more common 7805 there, floating its center pin above ground w/resistor to make it into a 6V reg, but I don't recommend doing that trick here, you need to nail 6V for this circuit and the 7806 does just that. 

73
Logged
KA5N
Member

Posts: 4380




Ignore
« Reply #2 on: January 30, 2011, 05:34:14 PM »

Your 7806 seemed to change to a 7808 and back to a 7806
in mid post. 
In case it is not clear to the questioner, the 78 is the series of the regulator and the 06 is the voltage.  So a 7808 is an eight volt
regulator and NOT what you need.
Allen
Logged
KE3WD
Member

Posts: 5689




Ignore
« Reply #3 on: January 30, 2011, 05:57:13 PM »

Ooops! 

Thanks KA5N for spotting -- and correcting -- the typo. 


73
Logged
N9MXY
Member

Posts: 240




Ignore
« Reply #4 on: February 09, 2011, 05:52:29 AM »

If you have trouble finding a 7806. A 7805 with 2 diodes properly oriented between gnd and the gnd pin of the IC will give you 6.2v out. 
Logged
KD5FPO
Member

Posts: 28




Ignore
« Reply #5 on: February 12, 2011, 07:18:03 PM »

I finally found time to work on my FT-101, and owe a big thank you to KE3WD et al,  the 7806 regulator mod worked perfectly, the PB1314 board now outputs a stable 6VDC, however that didn't seem to solve the larger problem of no VFO LED-no audio. This all began when I carelessly tapped on a front panel light bulb without turning off the rig and apparently shorted the bulbs 14 volts to ground with my clumsy finger. I remember seeing a small low voltage spark just as the audio hiss quit. Any ideas? It seems to me that this sort of thing must've happened to lots of others over the years. Michael, KD5FPO
Logged
KE3WD
Member

Posts: 5689




Ignore
« Reply #6 on: February 13, 2011, 06:41:23 AM »

Sounds like one of the other low voltage DC supplies has been damaged. 

Since it is exhibited in the Audio section, I'd take a look at the schematic, find the DC power voltage that powers that section and work backwards with the DMM looking for anomalies there.  Very likely you may have just popped a series resistor somewhere if lucky.  Such resistors will be rather low in value, such as the 100 ohm resistor on the audio board that is in series with the 13.5VDC line going to the Collector of Q3 as an example.  Doubtful this would happen to a larger value resistor, such as 1K, for a short as you describe wouldn't draw enough current to overheat the 1K. 

"Follow the power!"  --  DMM on DC Volts scale and look at all the lower level DC powerlines against the schematic voltages given, paing particular attention to any voltage that is shared by both of the circuits that are currently sick, the display and the audio I think is what you said, and you should find a clue as to where the one single thing that is stopping the show may be. 


73

Logged
KE3WD
Member

Posts: 5689




Ignore
« Reply #7 on: February 13, 2011, 06:46:34 AM »

If you have trouble finding a 7806. A 7805 with 2 diodes properly oriented between gnd and the gnd pin of the IC will give you 6.2v out. 

I don't recommend doing this in this particular circuit, simply because in this case, the voltage MUST be exactly at 6.0VDC for the circuits it powers to function correctly.  YMMV

I tried to cover that in my original posted directions above -  this is a "been there, done that" situation.  A ten-turn variable potentiometer placed in the same position as the diodes would be a better choice, but since adjustability of this circuit is not all that desirable, use of the 7806 simply nails the required voltage with the least problem IMO.  Of course, if all I had was a 7805 and a ten-turn pot in the junkbox, bet yer bippy it'd get implemented that way if it was my own rig.  However, a customer deserves me ordering and installing that 7806, a modification that does not require someone in future to kinow that there is a "hidden" adjustment in there...

73
Logged
KD5FPO
Member

Posts: 28




Ignore
« Reply #8 on: February 13, 2011, 07:43:17 AM »

Roger-wilco, I'll start tracing. It was the audio and the VFO LED that quit on the FT-101.  By the way, in case anyone needs one of the 7806's they're Mouser PN# 518-L7806CV. 1.5 Amp @ 0.67 cents each. Thanks for all the help, I'll keep you posted. 73 Michael
KD5FPO
Logged
KD5FPO
Member

Posts: 28




Ignore
« Reply #9 on: February 13, 2011, 10:21:42 AM »

Okay, back to the dead FT-101. After checking the fault tree in the svc. manual and seeing the rectifier board (PB1076) as being the first link in the chain to be checked, I found that the 13.5 VAC tap on that board reads 11.2 volts, as does the 10.5 volt tap. The +600VAC tap reads well over 1200 Volts, the 160 VAC tap reads over 240 Volts. So I'm going to pull the board and check components, it looks like a real you-know-what to get out of there. BTW, the 100 Ohm resistor in line with the collector of Q3 on the audio board reads 102.2 Ohms, so back it went. 73 Michael KD5FPO
Logged
KD5FPO
Member

Posts: 28




Ignore
« Reply #10 on: February 13, 2011, 11:19:22 AM »

Part four of the saga of the dead FT-101. I got the rectifier board (PB1076) free enough to look closely at it, all components look to be okay visually, nothing blistered, cracked, discolored, etc., EXCEPT for diodes D7 & D8. D7 took almost zero coaxing for it to break cleanly in two, D8 looks dark brown. Also the PCB trace beneath them that connects the +D7 to the +D8 is broken away, there's a 1/16th inch gap in the trace, but it doesn't look like it had gotten hot, it looks more like it was torn away. I've never seen a trace broken like this before, they usually show some signs of high heat. Anyway, the diodes are spec'd. as silicon V06B's, anyone know of a common replacement? would a 1N4002 work? Or perhaps something beefier?
Many thanks for any help. Michael KD5FPO
Logged
KE3WD
Member

Posts: 5689




Ignore
« Reply #11 on: February 13, 2011, 03:37:12 PM »

I keep a drawer full of 1N4007s handy for replacing all single rectifiers of this type. 

While the 1N4002 might be able to handle the voltage here, the 1kv rating of the '007s makes replacement of most all of these low voltage japanese rectifiers a "don't have to compare the specs" situation. 

You can use google to find out the ratings of the original EIAJ part number here, compare to the rating for the 1N4002 and if it is equal or greater, you can use it there.  Replace ALL rectifiers in any bridge where one or more has gone south. 

I didn't think it would be on the rectifier board because typically the failure mode of a rectifier in a bridge is a dead short, which blows fuses.  Sounds like someone may have replaced the fuse and hit it with power again, or perhaps the fuse in there is larger than it should be for the rectifiers to be cracked open and traces blown like that.  Yes, overcurrent can sometimes literally blow the trace to kingdom come without leaving a lot of carbon hanging around.  Repair the trace by soldering a jumper made from copper wire strand across it. 

73
Logged
KD5FPO
Member

Posts: 28




Ignore
« Reply #12 on: February 14, 2011, 06:55:06 AM »

Yup, that's my plan. I'm now waiting on the diodes to come in the mail.  It's interesting to note however that this was another one of those FT-101E's with 11 meters.  So many troubles in these radios were caused by CBers. The mode switch on mine was a REAL mess, the 6JS6C's output a best of 20 Watts on 14.2 MHz. The crystal deck was a hodgepodge of mixed crystals. "Let the buyer beware."  No wonder I paid only $100.00 for the rig! But after 8 years and a lot of TLC I had it working really well, until I got stupid and forgot to turn it off before tapping on a finicky panel bulb.  DUH! 
Logged
KE3WD
Member

Posts: 5689




Ignore
« Reply #13 on: February 15, 2011, 07:40:33 AM »

Even without prior modifications, legal or illegal, one must also take into account the aging of these things.  The ravages of time account for many problems, yours might be inclusive in there as perhaps at one time a tap on the pilot lamp would not likely have ended up shorting the supply.  Unless, of course you left out some clue, like that "tap" was done with someting conductive that also happened to short the line out...

At any rate, whenever someone brings a piece of older gear like that into the service shop, we try to explain to them that at some point, the concept of a simple repair must be juggled with the reality that the "repair" could easily equal a "restoration".  I try to build as much of that as possible into the estimate, allowing for addressing known items that are prone to failure for the certain model at hand.  Part of the reasoning behind that comes from the experience of taking in an older piece and addressing just the one customer complaint problem, such as a rather simple case of a shorted rectifier and blown internal fuse.  If you do just that and that only, expect a Callback on that piece because, once it is working again, the customer is very likely to work it like it was new, ridin' it hard and puttin' it up wet as it were - and that alone can push some of the other component parts into failure. 


But in your specific case, the educational experience alone is well worth your time and dollars here.  You are to be commended for that in this day and age of instant gratification and "throwin' money at it" solves. 

Just try to keep the situation at a point where you are always relaxed and having FUN while doing so, you are likely learning some things that you won't even realize until some time in the future when the recall of experience will kick in on a completely unrelated project. 

73
Logged
KD5FPO
Member

Posts: 28




Ignore
« Reply #14 on: February 18, 2011, 09:03:53 PM »

Thanks very much Clark. I agree with you 100%. As for my poor old FT-101 the new NTE116 diodes came, I installed them this afternoon, fixed the blown trace on the PCB, and Voila!  She works beautifully.  Cheesy It's like having an old friend back.
The panel lamps fit into bayonet sockets which have a spring loaded +14V pin that protrudes from the bottom of the socket, if the screw that secures the socket becomes loose - the socket will be loose also, and at that time the pin can easily touch the bracket that secures the assembly - shorting it out.
That's what happened to me. I recommend to everyone to insulate those pins with a small 3/8 inch long piece of shrink tubing to prevent the headache that it gave me.
The 6JS6C's are only making about 25 or so Watts full tilt on 10m, but I only need about 10W in order to drive the FTV-650B transverter.
The T-verter had hardly ever been used, so they're both sort of coasting along enjoying the easy life. Many "thank you's" to one and all for the advice and encouragement.   73 and good DX always. Michael KD5FPO
Logged
Pages: [1] 2 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!