Icom R71E Communications receiver

[Spartan888]

Everything works fine...memory card, frequency display, all knobs and buttons, lights, S-meter, etc. However there is no signal received on any band and no deflection of the S-meter on any frequency even though the meter is functioning ok (the S-meter moves when the gain or squelch controls are used).

When touching an antenna lead against either of the two antenna inputs, there is no reaction on the S-Meter or any electrical sound.

The previous owner thought it needed new electrolytic caps as it was working when put into storage. I think it is more likely to be a problem with the antenna input side because everything else on the set appears fine?

Question: On the RF circuit diagram attached, if DS1 and/or DS2 were blown, would this make the receiver completely deaf? I have a problem in the house with RFI and yet there is no hint of this when the set is turned on. The speaker emits a soft hum and reacts to the volume control.

The fact that no signal appears to be getting through suggests to me that both have blown, as it would be odd to have caps in both antenna circuits fail at the same time and prevent any signal getting through?

Sadly I stripped the heads on two of the top cover screws so cannot see the RF section yet. But I wanted to get opinions as to whether I am on the right track. The main issues on this set are usually caused by the back-up memory battery expiring but that is definitely not the case on this occasion.

[Radio Wrangler]

A memory has stirred in the back of my head...

Icom for period, made radios without permanent storage in ROM for the software of their microprocessors. Instead the software was loaded into a low current static RAM, held on power all the time using a lithium battery.

When the battery eventually fails, you don't just need a new battery, you also heed a copy of the set's internal software and a means of entering it.

I think the R71E is from this era, the transceiver in the series definitely was.

Be careful working on the set. A momentary shorting of the memory backup power line or battery can brick the thing, Various people have found ways around this, so a good internet search is wise.

Blown bulbs, DS1 and DS2 will block ALL antenna signals entering the set.

They are intended to! they act as fuses protecting the input. For lesser overloads, they act as protective PTC thermistors as their resistance increases as they heat up.

This set may have had some d*mned fool transmit straight into it. It's the popular way of blowing the protection bulbs. There may be other damage sustained in the time it took the filament to melt.

David

[deliverance]

Hi there is there any DC voltage on the antenna pl connection.

[Spartan888]

Yes, I researched the memory/battery matter and was comfortable that this was not part of my current problem. When I have the set working, I will revisit this subject. I hope to get the cover off soon so I can see DS1/DS2. The problem screw is directly above the antenna inputs, is rusty and seems there has been a tiny amount of water pooling around it at some time. If water seeped down and dropped on to the antenna connections or switch then that might be the issue.

[Spartan888]

Originally Posted by deliverance

Hi there is there any DC voltage on the antenna pl connection.

Central PL connection to chassis ground shows no DC voltage with set switched on.

[Ceeejay]

Originally Posted by Radio Wrangler

A memory has stirred in the back of my head...

Icom for period, made radios without permanent storage in ROM for the software of their microprocessors. Instead the software was loaded into a low current static RAM, held on power all the time using a lithium battery.

When the battery eventually fails, you don't just need a new battery, you also heed a copy of the set's internal software and a means of entering it.

David

Funny, i remember this being discussed on a different forum and I got involved in a project to re-write the NV RAM using an Arduino, I beleive there was some success too and the code was published.

Just recently I noticed there are boards available on eBay which reprogram the SRAM in those and other Icom radios of the time, there are even ways to add extra coverage by flipping a few bits in the RAM.

[Spartan888]

Finally got the covers off and there is no apparent water damage anywhere inside or any eveidence of any work being done.The two lamps in the RF section are not working but I cant see whether they have actually blown due to their location and the fact that they are so tiny. There is no DC showing at either antenna terminal. The previous owner was an experienced VK ham and said that the set was working when he put it into storage but that when he plugged it in a year later that the set did not show it was receiving anything. Everything else works fine, memory, frequency display, etc, etc. Maybe the volume is too soft though. What would cause BOTH lamps to blow or alternatively what would prevent both lamps from lighting up? (see circuit diagram in earlier post).

[frsimen]

The lamps won't light up in normal use, they act as a fuse should someone try transmitting into the aerial socket in error.

You can check the lamps for continuity with a multimeter, if you have one.

Paula