Used IC-R100 missing narrow FM mode

[kruser]

If the receiver is basically working, except for the narrow FM mode, it is unlikely replacing 54 capacitors will get you success.

I would suggest that the problem is an IF crystal like the two cans on the left with orange dots or the blue plastic cubes. Having the schematic and board layout would help identify which of these are for NFM vs WFM. Then the troubleshooting becomes easy. Get a disc capacitor like .05 uF or so, cut the leads to about 1/4 inch and glue it to a plastic stick. Then short out the outer leads of the IF crystals or ungrounded leads of the square filters and see if the squelch circuit suddenly behaves. Then solder the cap in that spot and test the radio. You will still need a replacement crystal to get proper bandwidth, but those are readily available. The problem could be elswhere in the logic that switches the IF chain, but more likley the crystal wore out or broke from the radio being dropped.

Exactly.
Basically what I mentioned in my first post about possible causes of the OPS symptoms given.
I used to break those plastic cased oscillators all the time in remote controls. They mostly used 455 kHz for remote controls so I always kept several of them in a part bin drawer. When a TV remote stopped working but had new batteries, it was almost a given that the oscillator had broken.

 

[LesWurk]

did you tune up or down from the expected frequency, many old Icom's are way off frequency

 

[SatHunter]

Thank you for all of the helpful advice! I’m going to try to unplug and plug all of the connections in today as suggested. I’ve tuned from 2M up to 174 mhz several times. The frequencies are very accurate but there is no signal on any frequency in FM mode. I’m going to check out the IF crystals as well, just need to get a ceramic cap to do the test. I bought a lot of components at an auction from a Radio Shack that went out of business many years ago. I have lots of resistors, ceramics and fuses. I’m not sure about electrolytics so it would likely be easier to buy the 54 cap kit online to get the correct sizes and values. I may do a video online demonstrating the performance of this unit & some of the techniques mentioned here to get it working properly again. It’s obvious that it was likely used as a mobile from the wear and tear on the outside of the case so the likelihood that it was dropped at least once is very possible.

 

[SatHunter]

I don’t know if this is of help to anyone. It’s from the service manual. They show a block diagram and have individual schematics for the various circuits.
I haven’t taken the top off yet but they show some of the key components on both sides of the board. The manual is about 20 pages In total.

 

[SatHunter]

I finally was able to order the proper power supply to match the R100. It was also 12V but has a whopping 3 amp circuit. Much to my surprise I tried some VHF Hi frequencies and the normal FM mode worked for a while. What seemed to make it stop responding was adjusting the squelch control. It feels really sloppy & I'm wondering if it isn't somehow affecting the reception in NFM mode. It doesn't look like the control is replaceable. Has anyone had a problem like this & did you find a way to repair it? Unplugging and plugging the power supply occasionally restores normal reception for a short period of time.

 

[RFI-EMI-GUY]

See post 20. It is likely the NFM IF crystal (s) , not the squelch control. You have low IF gain in NFM mode. Does the squelch work in AM or WFM mode?

 

[SatHunter]

See post 20. It is likely the NFM IF crystal (s) , not the squelch control. You have low IF gain in NFM mode. Does the squelch work in AM or WFM mode?

Good to hear from you again. I believe you are absolutely right. The squelch does function on WFM & AM. I wanted to try the capacitor you mentioned in that post a long time ago. I wasn't sure where exactly to touch the leads on the board. Where would a person be able to purchase the crystal from? Thanks again for your assistance!

 

[RFI-EMI-GUY]

Crystal filters are series elements. You would bridge the input and output with a ceramic disc cap , avoiding the ground pin. If the filter is bad, the reception will improve with a cap. You can buy parts from Digikey or Louder.

 

[SatHunter]

Crystal filters are series elements. You would bridge the input and output with a ceramic disc cap , avoiding the ground pin. If the filter is bad, the reception will improve with a cap. You can buy parts from Digikey or Louder.

So would I have to do this from the bottom of the PCB? I'd assume there is no access to the crystal from the topside. I've ordered from Digikey many times and always found the parts I've needed. What would the part be called so I know what to order? Thanks again!

 

[RFI-EMI-GUY]

So would I have to do this from the bottom of the PCB? I'd assume there is no access to the crystal from the topside. I've ordered from Digikey many times and always found the parts I've needed. What would the part be called so I know what to order? Thanks again!

Yes bottom of board is only access. Hopefully there are no soldered in place shields.

Comprehensive Service manual with schematic available here:

RigPix Database - Schematics, manuals 'n' stuff

www.rigpix.com

The scanning of schematics is a bit terrible, you might have to piece them together with tape or just use your head to figure out the continuity.

See theory sections 4.2.2 and 4.2.3 . I would concentrate on the functionality of IC1 (MC3357P FM receiver) , F13 and work back to F12 (comprised of two filters) and F11. There is a pot R142 that sets gain into IC1 which may be a concern if set too low. Use a disc cap .001 uF or so to bridge the filters to see if the gain changes.

The parts are crystal filters or monolithic crystal filters. F13 is usually a Murata part.

X1 and X2 are standard crystals and could also be failed. X2 is the discriminator crystal and likely bridging it will not prove much.

 

[SatHunter]

Yes bottom of board is only access. Hopefully there are no soldered in place shields.

Comprehensive Service manual with schematic available here:

RigPix Database - Schematics, manuals 'n' stuff

www.rigpix.com

The scanning of schematics is a bit terrible, you might have to piece them together with tape or just use your head to figure out the continuity.

See theory sections 4.2.2 and 4.2.3 . I would concentrate on the functionality of IC1 (MC3357P FM receiver) , F13 and work back to F12 (comprised of two filters) and F11. There is a pot R142 that sets gain into IC1 which may be a concern if set too low. Use a disc cap .001 uF or so to bridge the filters to see if the gain changes.

The parts are crystal filters or monolithic crystal filters. F13 is usually a Murata part.

X1 and X2 are standard crystals and could also be failed. X2 is the discriminator crystal and likely bridging it will not prove much.

Thank you very much for explaining everything to me. I have low vision so I’m going to have to recruit some help to check things out. At the times it’s working right it is a very robust receiver. Do you think it makes a difference that I’m using a 12V power supply instead of a 13.8 unit? Going to do my best to get it up and running.

 

[RFI-EMI-GUY]

Thank you very much for explaining everything to me. I have low vision so I’m going to have to recruit some help to check things out. At the times it’s working right it is a very robust receiver. Do you think it makes a difference that I’m using a 12V power supply instead of a 13.8 unit? Going to do my best to get it up and running.

If the 12V power supply is well regulated and filtered at should be fine. Bear in mind that there are wall warts and even Radio Shack "12V" power supplies that are mediocre.

 

[SatHunter]

All of a sudden the radio died. Hooked up the power adapter, installed new batteries - nothing. Took the back off & did a visual inspection & can't see any physical problems to the circuitry. I wasted a lot of time on this scanner. I may have to retire it and put it aside for parts (battery compartment, knobs, case, ect.) It's a shame - my son wanted to use it for air and rail - I wouldn't have any idea where to start for a repair like this ☹️

 

[SatHunter]

All of a sudden the radio died. Hooked up the power adapter, installed new batteries - nothing. Took the back off & did a visual inspection & can't see any physical problems to the circuitry. I wasted a lot of time on this scanner. I may have to retire it and put it aside for parts (battery compartment, knobs, case, ect.) It's a shame - my son wanted to use it for air and rail - I wouldn't have any idea where to start for a repair like this ☹️

I realized today that I posted this in the wrong thread. This post was regarding the Realistic Pro 30 handheld which gave up the ghost many months ago.

Now in regard to the Icom - I connected it to power & antenna once again this morning. Turned it on and no narrow FM as usual. Cleaned the controls with De-oxit. Nice quiet smooth volume & squelch controls. I tapped the top of the case and all of a sudden sound came out & the radio worked perfectly on FM narrow for hours. About 10 minutes ago it went silent again. I gave It another tap & it started working again. Any idea what I could look for or try if I take the lid off again?
Possibly a dirty connector? Very happy that there is hope to resurrect this little guy

 

[RFI-EMI-GUY]

I realized today that I posted this in the wrong thread. This post was regarding the Realistic Pro 30 handheld which gave up the ghost many months ago.

Now in regard to the Icom - I connected it to power & antenna once again this morning. Turned it on and no narrow FM as usual. Cleaned the controls with De-oxit. Nice quiet smooth volume & squelch controls. I tapped the top of the case and all of a sudden sound came out & the radio worked perfectly on FM narrow for hours. About 10 minutes ago it went silent again. I gave It another tap & it started working again. Any idea what I could look for or try if I take the lid off again?
Possibly a dirty connector? Very happy that there is hope to resurrect this little guy

Probably one of the crystals is intermittent. I find that a fine bristle artists paintbrush can be used to wipe parts in a circuit and reveal ones that are mechanically intermittent.

 

[SatHunter]

Probably one of the crystals is intermittent. I find that a fine bristle artists paintbrush can be used to wipe parts in a circuit and reveal ones that are mechanically intermittent.

Greatly appreciate! I’ll give that a try tonight

 

[SatHunter]

Probably one of the crystals is intermittent. I find that a fine bristle artists paintbrush can be used to wipe parts in a circuit and reveal ones that are mechanically intermittent.

I tried your technique last night. Having problems getting the top lid off I focused on the bottom of the circuit board. I isolated the problem to the front of the Icom. I got the receiver to light up by brushing & then tapping on a connector with 4 wires attached to it. Thinking it needed cleaning I used 404B, reconnected, turned the radio on, left it for a half hour & it worked the whole time. Put the Icom back together, turned it on & not working again. Tapping the radio temporarily brought the FM mode back till it cut out again. Photo of suspected problem included.

 

[RFI-EMI-GUY]

maybe cracked solder on the reverse side. sometimes solder does not wick well to steel pins of a jack and over time will crack.

 

[SatHunter]

maybe cracked solder on the reverse side. sometimes solder does not wick well to steel pins of a jack and over time will crack.

Excellent suggestion. I will get the top cover off tomorrow and do a close inspection of the board. I don’t think the top was ever taken off of it so it’s fitting very tight. I’ll just have to take some time & remove it carefully

 

[dlwtrunked]

did you tune up or down from the expected frequency, many old Icom's are way off frequency

Also, make certain you are using the correct antenna connection. I owned tow of these at one time but got rid of them as I never used them since they do not have single-sideband.