R-71a failing

[DaveNF2G]

Here's an update. Based on a discussion over in the R71a Yahoogroup, I ordered a specific DigiKey part that was supposed to replace the DC-DC converter on the matrix board. After disassembling my receiver, I found that the converter in the radio is a large silver box with (apparently) two connection points. The DigiKey part is a little black chip with 3 leads, kind of like a flat transistor. No way it will connect in place of the original unit.

So, back to square 1, or maybe -1 as my R71a is now in several pieces. What I'm looking for now is someone with an Icom receiver that is otherwise unusable from which the DC-DC converter can be harvested.

 

[dkf435]

There have been a few on Ebay starting at $49 and $99 from the Israel source and recently another one parted out in the US on Ebay also. There are several being sold from the stack of 30 from the China source also on Ebay.

David

 

[DaveNF2G]

Thanks. I will unrestrict my search there and try again. (I usually search US Only locations.)

I would even be willing to buy a whole functioning matrix board.

 

[skywarrior]

Dave,
Try this service company, was a former Icom tech, SultanTronics Radio Repair and Technical Design Services

 

[DaveNF2G]

I've checked with Icom and several repair shops. The parts I need (either the DP-2 itself or the whole matrix board) are no longer available anywhere. I have decided to scrap the R-71a and start looking for another receiver. I still want an Icom because I have the CI-V equipment and an R-7000.

 

[k9rzz]

Willing to sell it for parts? =:^]

 

[DaveNF2G]

Maybe, but the shipping is ridiculous for a non-working radio IMO.

 

[DaveNF2G]

I just got info via the Yahoogroup about how the DigiKey part is supposed to be connected to the R-71a, so I am going to attempt the surgery again.

 

[dawgy]

Easy fix on the DP-2 IC 6 replacement. Buy the Digi Key part listed on yahoo, it is a 9 volt 7805 3 pin chip the cost is about $10 with shipping.

Use an R71 schematic for the "Matrix Board" unit. The old DP2 unit should have some clear silicone holding it to the board. The pin closest to the silicone end is the (-10V) lead and is connected to R28 which is a 1K ohm resistor on back side of board on my unit. The other side of R28 is ground. The middle pin of the DP-2 is "ground" and the pin furthest from the silicone side is the (+13.8V) lead and is connected to C119 and L2.

Ok, now the easy part after removing DP-2. On the Digi Key 9V 7805 there are 3 pins. Pin 1 is closest to the dot.

Turn the 7805 upside down and remember pin positions. It makes it easier to connect to new locations and avoid shorts.

New Pin 1 connects to the (+13.8) hole, Pin 2 connects to (Ground) hole and also solders to the grounded side of R28 (1k). Pin 3 connects to (-10V).

You will need to extend the wires from the 7805 pins in order to reach the old pin holes. I used long ends of resistors to extend and solder the wires to the holes where they needed to go. The 7805 is much smaller and sits in the same location of the old DP-2 unit.

Skill level required, (not much) if you can follow these directions and have a schematic just to verify my instructions, you can do this change out in 10 minutes or less. It takes longer to reconnect the J connectors than to solder the 7805.

Unfortunately, I spent 2 weeks going over every single circuit on unit until I found the faulty DP-2. My DP-2 was only partially failing. The S meter was only deflecting mid-scale and not full scale like a blown DP-2 does.

After 30 years, my R71A is still getting it done on Utility DX! No need to get an SDR radio, cause the .15uV SSB reception still beats most expensive SDR units out there by a wide margin. I sold my Perseus SDR after comparing it to my 1984 R71-A. (Serial #1104)

Don't give up on this awesome R71 receiver, it is very easy to fix with a schematic and is easy to work on with a solder gun.

I hope this helps you fix your radio. You will be pleased when you hear if fire up again!

Good Luck,
73's

Sy

 

[ridgescan]

Shoot Sy-after your post I went and gave my 71a a HUG

 

[k9rzz]

Put that post in the Wiki!

My Chinese R71E is still running like a champ. Love it.

 

[EricCottrell]

Hello,

Finding special parts for old radios can be a pain. A friend of mine bought a Yaesu FRG-7700 receiver and the digital display did not work. I tried to fix it, but found the frequency counter ic was bad. The IC was used in a number of radios of the same vintage, but has been unavailable for years.

The internet is very useful with service information and groups dealing with the radio. I own a number of older radios and I am always on the lookout for good "for parts" deals.

73 Eric

 

[DaveNF2G]

I still have the R71a. I was deciding whether to keep it for parts or tear it down and sell the parts. Looks like now I might have another option.

 

[ElroyJetson]

A few R71s have crossed my repair bench. I absolutely hate those things.

At this point in the game they're all failing or about to fail, they are obscenely difficult to work on,
and parts availability is really bad.

If yours fails, I suggest buying a new radio. The old R71s are not worth the repair hassles involved.

 

[dawgy]

Elroy, obviously, you must not like the Icom R71 since anyone with a freely available online schematic can troubleshoot this radio with ease.

Sure the parts are becoming obsolete, but someone with an electronics background can read up on discrete data sheets and find components similar to an obsolete part.

Take the RF board for instance, the Q3 & Q4 mixers (2SK125 FETs) are gone and are subject to blow during thunderstorms if the DS0 or DS1 fuses don't blow first. Pull out some J310 FET's and replace them and you are back in business.

Take the PLL board, change out the capacitors that run hot from the 8V regulator usually C130 & C129 and that corrects half of (decimal point display only) display problems. You can buy a complete capacitor kit on ebay for $40 for the entire radio.

Matrix Boards, easy fix too as see above.

Power Supply board, yes it runs hot with inadequate ventilation but it is easily repairable with cheap bridge rectifiers, capacitors and even replacement transformers. Best bet, uncap the pigtail connector and use a 12V DC power supply and eliminate heat and further problems.

I could go on, but people get the point. These radios are serviceable and user friendly if you know what you are doing.

Final point, I am not an electronic repair man. I am just an EE who likes to understand how thing work.

BTW, ridgescan, that is one hell of a SX-88 you have there! Nothing like the smoothness of warm vacuum tubes glowing while listening to BCB back in the day. 7 Eleven vacuum tube test machines are a distant memory and I am only 50! $600 bucks back in 1954 was a true luxury item!

Take care guys and fix those radios!

 

[ridgescan]

BTW, ridgescan, that is one hell of a SX-88 you have there! Nothing like the smoothness of warm vacuum tubes glowing while listening to BCB back in the day. 7 Eleven vacuum tube test machines are a distant memory and I am only 50! $600 bucks back in 1954 was a true luxury item!

+1 thanks. It'd supposedly be like spending about $5000 on a receiver today. It has cleaner audio than my r75 and r71a with EEB mods, and as a result, MW is way nicer on it as well as weaker SW BCs. SSB is still pretty stable too.
I am lucky.
Back to topic, if and when my 71a fails, it will be brought back to operating status. It is a fantastic rig and worth a second chance.

 

[ElroyJetson]

The couple that crossed my bench usually either needed parts that were no longer available or had so many failures that it would have cost more in labor hours to fix it than the value of the radio after repairs were completed.

I was able to fix one or two but the customers declined the high cost of repairing the others.

I'm glad. Those ARE pigs to work on.

The first time I opened one up, the words that came out of my mouth were "Nest of snakes...."

 

[k9rzz]

It's a labor of love . Some guys will tear a car down to the bare frame and rebuild it, other's will get rid of a car as soon as it's a year old. :^) I had an R-71a that had all sorts of mods including copper shielding around extra IF filters. The front end was like a tank. I'm hoping to get my current one to that point. Should run circles around a stock R75 which is all surface mount parts, very hard to fix. We all have our hates and passions.

 

[ElroyJetson]

To me working on those was just a job. Not one I particularly enjoyed.

I love repairing stuff but I don't like working on stuff that's a nest of wires.

As for passion, my passion and favorite hobby is building guitars.

 

[DaveNF2G]

New Pin 1 connects to the (+13.8) hole, Pin 2 connects to (Ground) hole and also solders to the grounded side of R28 (1k). Pin 3 connects to (-10V).

I've been struggling to verify hole and component positions on the matrix board and schematic. My close range vision is not what it used to be. Here is a photo of the solder side of the matrix board. The pads at the bottom left are R28. The vacated holes from DP2
are visible - one near R28 and the other two almost at the left edge of the board.

If I understand the directions and layout correctly, the new component would be oriented as pin 1, 2 and 3 from top to bottom in the photo view. Is that right?