Re: UHF Range: Partial RX/TX Issue.
The current drawn from the power supply is also a good indicator, ideal current on UHF TX on min RF? is aroubd 2.5 Amps, at 50 Watts expect 12-15 Amps on FM or CW. PA is around 50 % efficient.
Most ham shacks should have what I call the minimum amount of kit:
Power supply 30 A with Voltage and current meters. Also a small variable 0 to 30V 2Amp with current limit.
DVM I/P to 20 A and 1 mV/A 750V AC/ DC
Oscilloscope 100MHZ? bandwidth (very cheap now days)
SWR meter or and an ATU that is metered?
50 ohn load 100 watts
Tina SA Spectrum Analyser (?60)
SDR RX SDR Play 1A
SMA, Pl259, BNC and N adapter set
Various hook up cables
With the above list you can repair and fault find a lot of radios, all costing less than one rig!!
73 Andrew G8UUG
Get
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Re: UHF Range: Partial RX/TX Issue.
For that radio, I found the best SWR/Wattmeter would be the Daiwa CN-801 which covers 140-525 Mhz, Full scale, 200 watts.
Bill
K2WH ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Richard via groups.io
Sent: Sunday, September 04, 2022 9:35 PM
To: [email protected]
Subject: Re: [YaesuFT847] UHF Range: Partial RX/TX Issue. ? Bill K2WH-> Hi Bill, I only just discovered the inability to enable the Alaska emergency frequency during a complete functionality check of the radio.? I went thru all the settings to see what was & what wasn't working on my radio.? I needed a full picture of what the radio could & couldn't do.? But yeah, I have no need for it.
Andrew-> I'm unsure about actual power out as I have no way of measuring VHF & UHF at the moment.? I've been looking at some cross needle SWR/PWR meters for those bands but haven't made a decision on which one to get.? I did get a neighbour to walk down the street to a park about 200m away with an FRS radio and he reports full quieting on minimum power.
I followed your link and sure enough it's been opened up.? I'm not too impressed, I? actually said "oh, bloody hell" as I specifically asked about this and the seller assured me it was untouched.? Oh well.? I'll be restoring it back to factory original.? Looks like all I have to do is remove the solder-shorts on pads #2 and #3 and put a chip resistor back on pad #6.
I feel like an idiot as I've had the radio this long and never noticed it could go out of band.? Never had a need to so I never tried.? Heh.
Spence M0STO -> I had the same thought about the relays.? I had my ear to the radio case listening for the tell-tale "click" as I tuned up & out of a BPF and into the next one.? I heard none.? That's when I had the thought that i'd need to look in this area.? Ah-ha!? look at that, "420 - 460 MHZ" circled in red on that schematic snapshot.? Dead-on the problem i'm having.? Thank-you for narrowing it down for me.
I do plan to replace the HF BPF diodes with low noise Schottky type as explained here:?
------
Examining the bottom board, I did see left of X1001 a soldering job that looked non-original and there was still a bit of flux around it. -- Bill, K2WH
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Re: UHF Range: Partial RX/TX Issue.
Richard.
Have a look at? for jumper settings. Depending what your band plan is, it is easy to see what the radio will TX from his listing.
You have suggested links fitted at 1,4,5,6 which would limit 2 metres to 144 to 146 Mhz. I? think you need 1,5, 6
The chip resistors are zero ohm, hence the solder
Bill K2WH-> Hi Bill, I only just discovered the inability to enable the Alaska emergency frequency during a complete functionality check of the radio.? I went thru all the settings to see what was & what wasn't working on my radio.? I needed a full picture of what the radio could & couldn't do.? But yeah, I have no need for it.
Andrew-> I'm unsure about actual power out as I have no way of measuring VHF & UHF at the moment.? I've been looking at some cross needle SWR/PWR meters for those bands but haven't made a decision on which one to get.? I did get a neighbour to walk down the street to a park about 200m away with an FRS radio and he reports full quieting on minimum power.
I followed your link and sure enough it's been opened up.? I'm not too impressed, I? actually said "oh, bloody hell" as I specifically asked about this and the seller assured me it was untouched.? Oh well.? I'll be restoring it back to factory original.? Looks like all I have to do is remove the solder-shorts on pads #2 and #3 and put a chip resistor back on pad #6.
I feel like an idiot as I've had the radio this long and never noticed it could go out of band.? Never had a need to so I never tried.? Heh.
Spence M0STO -> I had the same thought about the relays.? I had my ear to the radio case listening for the tell-tale "click" as I tuned up & out of a BPF and into the next one.? I heard none.? That's when I had the thought that i'd need to look in this area.? Ah-ha!? look at that, "420 - 460 MHZ" circled in red on that schematic snapshot.? Dead-on the problem i'm having.? Thank-you for narrowing it down for me.
I do plan to replace the HF BPF diodes with low noise Schottky type as explained here:?
------
Examining the bottom board, I did see left of X1001 a soldering job that looked non-original and there was still a bit of flux around it.
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Re: UHF Range: Partial RX/TX Issue.
Check the DC switching voltages toggle as you change frequency? this will give a clue if the logic is switching correctly?
73
Andrew
Get
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Re: UHF Range: Partial RX/TX Issue.
Sounds like you are making progress you will get there, the pin diode mod does bring down the noise very noticeable.
You also need a 50 Watt dummy load to go with your srw meter
BR
Andrew
Bill K2WH-> Hi Bill, I only just discovered the inability to enable the Alaska emergency frequency during a complete functionality check of the radio.? I went thru all the settings to see what was & what wasn't working on my radio.? I needed a full picture of what the radio could & couldn't do.? But yeah, I have no need for it. Andrew-> I'm unsure about actual power out as I have no way of measuring VHF & UHF at the moment.? I've been looking at some cross needle SWR/PWR meters for those bands but haven't made a decision on which one to get.? I did get a neighbour to walk down the street to a park about 200m away with an FRS radio and he reports full quieting on minimum power. I followed your link and sure enough it's been opened up.? I'm not too impressed, I? actually said "oh, bloody hell" as I specifically asked about this and the seller assured me it was untouched.? Oh well.? I'll be restoring it back to factory original.? Looks like all I have to do is remove the solder-shorts on pads #2 and #3 and put a chip resistor back on pad #6. I feel like an idiot as I've had the radio this long and never noticed it could go out of band.? Never had a need to so I never tried.? Heh. Spence M0STO -> I had the same thought about the relays.? I had my ear to the radio case listening for the tell-tale "click" as I tuned up & out of a BPF and into the next one.? I heard none.? That's when I had the thought that i'd need to look in this area.? Ah-ha!? look at that, "420 - 460 MHZ" circled in red on that schematic snapshot.? Dead-on the problem i'm having.? Thank-you for narrowing it down for me. I do plan to replace the HF BPF diodes with low noise Schottky type as explained here:? ------ Examining the bottom board, I did see left of X1001 a soldering job that looked non-original and there was still a bit of flux around it.
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Re: UHF Range: Partial RX/TX Issue.
Bill K2WH-> Hi Bill, I only just discovered the inability to enable the Alaska emergency frequency during a complete functionality check of the radio.? I went thru all the settings to see what was & what wasn't working on my radio.? I needed a full picture of what the radio could & couldn't do.? But yeah, I have no need for it.
Andrew-> I'm unsure about actual power out as I have no way of measuring VHF & UHF at the moment.? I've been looking at some cross needle SWR/PWR meters for those bands but haven't made a decision on which one to get.? I did get a neighbour to walk down the street to a park about 200m away with an FRS radio and he reports full quieting on minimum power.
I followed your link and sure enough it's been opened up.? I'm not too impressed, I? actually said "oh, bloody hell" as I specifically asked about this and the seller assured me it was untouched.? Oh well.? I'll be restoring it back to factory original.? Looks like all I have to do is remove the solder-shorts on pads #2 and #3 and put a chip resistor back on pad #6.
I feel like an idiot as I've had the radio this long and never noticed it could go out of band.? Never had a need to so I never tried.? Heh.
Spence M0STO -> I had the same thought about the relays.? I had my ear to the radio case listening for the tell-tale "click" as I tuned up & out of a BPF and into the next one.? I heard none.? That's when I had the thought that i'd need to look in this area.? Ah-ha!? look at that, "420 - 460 MHZ" circled in red on that schematic snapshot.? Dead-on the problem i'm having.? Thank-you for narrowing it down for me.
I do plan to replace the HF BPF diodes with low noise Schottky type as explained here:?
------
Examining the bottom board, I did see left of X1001 a soldering job that looked non-original and there was still a bit of flux around it.
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Re: UHF Range: Partial RX/TX Issue.
Check this section. it shows the cutoff for each frequency you mention and I believe?this is where you need to start to conduct some tests..
On Sun, Sep 4, 2022 at 6:46 PM Spence M0STO via <unavailable.equal= [email protected]> wrote:
Just chucking this out there but surely the signal passes through the 70cm BPF? If anything in the 70cm BPF has come adrift then the radio will have a broken signal path. Is it possible soon as you go to 460mhz a relays (pin diodes) on nearly all radios switch out the BPF and onward. If the switching at 460mhz has switched out the bad BPF then this may be why it suddenly bursts into life.
? I believe the diodes (noisy diodes are 1N5711 or BAT85’s) so may be worth checking those and the BPF relays.
? I’m trying to find a schematic for the FT847 but only find the technical supplement.
? I will tune my FT847 near 460mhz and listen to any switching but I’m sure it does as it’s the beginning of band IV tv transmissions here in the UK before DVB-T
de Spence M0STO Sent while portable! please excuse typos. On 4 Sep 2022, at 15:02, Andrew Lenton < a@...> wrote: I have further read this, and it makes no sense, it seems you have a corruption, or an illegal settings near the CPU ? Check this site and let me know what you find: ?
? 73 ? Andrew ? ? Hi all, I have a rather strange issue with my '847 that I haven't yet figured out the cause for: It doesn't receive or transmit between 420 MHz and 459..9995 MHz.
Background info: I'm 3rd owner of my nearly mint condx.? My understanding is that it has never been modded or altered in anyway.? An examination of some of the circuit boards shows no signs of tampering/repair or component damage. The radio functions perfectly in every sense, transmits and receives in all 5 modes without issues on all amateur bands (except 440 MHz band of course) and receives perfectly fine on HF and VHF general coverage receive, and receives perfectly fine at 460 MHz up to 512 MHz.? No other anomalous functionality except that I just discovered during my trouble shooting session that I cannot enable the Alaska 5167 kHz emergency channel in the menu, and that my radio will transmit at 460 Mhz and up.? That last bit piques my attention as my understanding is that these radios cannot transmit out of band unless someone has done a mod?
When I select any 70 cm frequency and key the radio, the speaker audio cuts off normally and I hear the cooling fan step up in speed from it's normal stand-by cooling speed like it normally does on any other band.? "Transmit" appears on the display, but no PO level, nothing, no matter what mode I use.? Using a couple of dual band radios confirmed to be working (I hear them perfectly on a pair of Icom R7000's) there is a definite gap between 420 MHz and 459.9995 MHz where nothing is heard or can be sent.? But the moment I go to 460 MHz and higher it will receive and transmit.? I do not hear a change in the receive static in the affected frequency region as I scroll up in frequency.? I've performed the CPU reset with no resulting change in behaviour.? Owned the radio for over 5 years but i've never used it on 440 MHz before so I do not know how long this issue has existed.
Any ideas before I break out the magnifying glasses and schematics? This email has been scanned by BullGuard antivirus protection.
For more info visit
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Re: UHF Range: Partial RX/TX Issue.
Just chucking this out there but surely the signal passes through the 70cm BPF? If anything in the 70cm BPF has come adrift then the radio will have a broken signal path. Is it possible soon as you go to 460mhz a relays (pin diodes) on nearly all radios switch out the BPF and onward. If the switching at 460mhz has switched out the bad BPF then this may be why it suddenly bursts into life.
? I believe the diodes (noisy diodes are 1N5711 or BAT85’s) so may be worth checking those and the BPF relays.
? I’m trying to find a schematic for the FT847 but only find the technical supplement.
? I will tune my FT847 near 460mhz and listen to any switching but I’m sure it does as it’s the beginning of band IV tv transmissions here in the UK before DVB-T
de Spence M0STO Sent while portable! please excuse typos.
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On 4 Sep 2022, at 15:02, Andrew Lenton < a@...> wrote: I have further read this, and it makes no sense, it seems you have a corruption, or an illegal settings near the CPU ? Check this site and let me know what you find: ?
? 73 ? Andrew ? ? Hi all, I have a rather strange issue with my '847 that I haven't yet figured out the cause for: It doesn't receive or transmit between 420 MHz and 459..9995 MHz.
Background info: I'm 3rd owner of my nearly mint condx.? My understanding is that it has never been modded or altered in anyway.? An examination of some of the circuit boards shows no signs of tampering/repair or component damage. The radio functions perfectly in every sense, transmits and receives in all 5 modes without issues on all amateur bands (except 440 MHz band of course) and receives perfectly fine on HF and VHF general coverage receive, and receives perfectly fine at 460 MHz up to 512 MHz.? No other anomalous functionality except that I just discovered during my trouble shooting session that I cannot enable the Alaska 5167 kHz emergency channel in the menu, and that my radio will transmit at 460 Mhz and up.? That last bit piques my attention as my understanding is that these radios cannot transmit out of band unless someone has done a mod?
When I select any 70 cm frequency and key the radio, the speaker audio cuts off normally and I hear the cooling fan step up in speed from it's normal stand-by cooling speed like it normally does on any other band.? "Transmit" appears on the display, but no PO level, nothing, no matter what mode I use.? Using a couple of dual band radios confirmed to be working (I hear them perfectly on a pair of Icom R7000's) there is a definite gap between 420 MHz and 459.9995 MHz where nothing is heard or can be sent.? But the moment I go to 460 MHz and higher it will receive and transmit.? I do not hear a change in the receive static in the affected frequency region as I scroll up in frequency.? I've performed the CPU reset with no resulting change in behaviour.? Owned the radio for over 5 years but i've never used it on 440 MHz before so I do not know how long this issue has existed.
Any ideas before I break out the magnifying glasses and schematics? This email has been scanned by BullGuard antivirus protection.
For more info visit
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Re: UHF Range: Partial RX/TX Issue.
Many years ago, I had an 847 and the previous owner modded it and it virtually transmitted anywhere. ? However, I do not think it would go beyond 512 mhz, xmit or receive. ? Of course, this was year ago and why would you want to turn on the? Alaska emergency frequency? ? K2WH ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Andrew Lenton
Sent: Sunday, September 04, 2022 10:02 AM
To: [email protected]
Cc: 'Max Donoghue'
Subject: Re: [YaesuFT847] UHF Range: Partial RX/TX Issue.? I have further read this, and it makes no sense, it seems you have a corruption, or an illegal settings near the CPU ? Check this site and let me know what you find: ?
? 73 ? Andrew ? ? Hi all, I have a rather strange issue with my '847 that I haven't yet figured out the cause for: It doesn't receive or transmit between 420 MHz and 459..9995 MHz.
Background info: I'm 3rd owner of my nearly mint condx.? My understanding is that it has never been modded or altered in anyway.? An examination of some of the circuit boards shows no signs of tampering/repair or component damage. The radio functions perfectly in every sense, transmits and receives in all 5 modes without issues on all amateur bands (except 440 MHz band of course) and receives perfectly fine on HF and VHF general coverage receive, and receives perfectly fine at 460 MHz up to 512 MHz.? No other anomalous functionality except that I just discovered during my trouble shooting session that I cannot enable the Alaska 5167 kHz emergency channel in the menu, and that my radio will transmit at 460 Mhz and up.? That last bit piques my attention as my understanding is that these radios cannot transmit out of band unless someone has done a mod?
When I select any 70 cm frequency and key the radio, the speaker audio cuts off normally and I hear the cooling fan step up in speed from it's normal stand-by cooling speed like it normally does on any other band.? "Transmit" appears on the display, but no PO level, nothing, no matter what mode I use.? Using a couple of dual band radios confirmed to be working (I hear them perfectly on a pair of Icom R7000's) there is a definite gap between 420 MHz and 459.9995 MHz where nothing is heard or can be sent.? But the moment I go to 460 MHz and higher it will receive and transmit.? I do not hear a change in the receive static in the affected frequency region as I scroll up in frequency.? I've performed the CPU reset with no resulting change in behaviour.? Owned the radio for over 5 years but i've never used it on 440 MHz before so I do not know how long this issue has existed.
Any ideas before I break out the magnifying glasses and schematics? ? This email has been scanned by BullGuard antivirus protection. -- Bill, K2WH
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Re: UHF Range: Partial RX/TX Issue.
I have further read this, and it makes no sense, it seems you have a corruption, or an illegal settings near the CPU ? Check this site and let me know what you find: ?
? 73 ? Andrew ?
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From: [email protected] <[email protected]> On Behalf Of Richard via groups.io
Sent: 04 September 2022 05:16
To: [email protected]
Subject: [YaesuFT847] UHF Range: Partial RX/TX Issue.? Hi all, I have a rather strange issue with my '847 that I haven't yet figured out the cause for: It doesn't receive or transmit between 420 MHz and 459..9995 MHz.
Background info: I'm 3rd owner of my nearly mint condx.? My understanding is that it has never been modded or altered in anyway.? An examination of some of the circuit boards shows no signs of tampering/repair or component damage. The radio functions perfectly in every sense, transmits and receives in all 5 modes without issues on all amateur bands (except 440 MHz band of course) and receives perfectly fine on HF and VHF general coverage receive, and receives perfectly fine at 460 MHz up to 512 MHz.? No other anomalous functionality except that I just discovered during my trouble shooting session that I cannot enable the Alaska 5167 kHz emergency channel in the menu, and that my radio will transmit at 460 Mhz and up.? That last bit piques my attention as my understanding is that these radios cannot transmit out of band unless someone has done a mod?
When I select any 70 cm frequency and key the radio, the speaker audio cuts off normally and I hear the cooling fan step up in speed from it's normal stand-by cooling speed like it normally does on any other band.? "Transmit" appears on the display, but no PO level, nothing, no matter what mode I use.? Using a couple of dual band radios confirmed to be working (I hear them perfectly on a pair of Icom R7000's) there is a definite gap between 420 MHz and 459.9995 MHz where nothing is heard or can be sent.? But the moment I go to 460 MHz and higher it will receive and transmit.? I do not hear a change in the receive static in the affected frequency region as I scroll up in frequency.? I've performed the CPU reset with no resulting change in behaviour.? Owned the radio for over 5 years but i've never used it on 440 MHz before so I do not know how long this issue has existed.
Any ideas before I break out the magnifying glasses and schematics?
This email has been scanned by BullGuard antivirus protection.
For more info visit
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Re: UHF Range: Partial RX/TX Issue.
My goodness this is an interesting fault, how much power do you get at 460MHz and akso6at the lower frequencies it does transmit at?
Get
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UHF Range: Partial RX/TX Issue.
Hi all, I have a rather strange issue with my '847 that I haven't yet figured out the cause for: It doesn't receive or transmit between 420 MHz and 459..9995 MHz.
Background info: I'm 3rd owner of my nearly mint condx.? My understanding is that it has never been modded or altered in anyway.? An examination of some of the circuit boards shows no signs of tampering/repair or component damage. The radio functions perfectly in every sense, transmits and receives in all 5 modes without issues on all amateur bands (except 440 MHz band of course) and receives perfectly fine on HF and VHF general coverage receive, and receives perfectly fine at 460 MHz up to 512 MHz.? No other anomalous functionality except that I just discovered during my trouble shooting session that I cannot enable the Alaska 5167 kHz emergency channel in the menu, and that my radio will transmit at 460 Mhz and up.? That last bit piques my attention as my understanding is that these radios cannot transmit out of band unless someone has done a mod?
When I select any 70 cm frequency and key the radio, the speaker audio cuts off normally and I hear the cooling fan step up in speed from it's normal stand-by cooling speed like it normally does on any other band.? "Transmit" appears on the display, but no PO level, nothing, no matter what mode I use.? Using a couple of dual band radios confirmed to be working (I hear them perfectly on a pair of Icom R7000's) there is a definite gap between 420 MHz and 459.9995 MHz where nothing is heard or can be sent.? But the moment I go to 460 MHz and higher it will receive and transmit.? I do not hear a change in the receive static in the affected frequency region as I scroll up in frequency.? I've performed the CPU reset with no resulting change in behaviour.? Owned the radio for over 5 years but i've never used it on 440 MHz before so I do not know how long this issue has existed.
Any ideas before I break out the magnifying glasses and schematics?
|
Re: MH-36D Microphone puzzle
Hi Max,
So, you're connecting the mike ground pin to the chassis through the
connector shell??
Chassis ground should be the same as pin 5, no?? They're separated
now, but I had originally connected the two ground pins (5 & 7)
together, and that didn't help.? Grounding is kind of magic,
however, so I suppose it's worth the try.
Thanks,
Greg? KO6TH
Max Donoghue wrote:
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Hi Greg,
Not sure if you have tried this but it has worked for me in the
past.
Take the mic connector apart and solder a bare 2" or so length of
wire to pin 7. Route the other end of the wire back through the
mic plug and wrap it around one of the screws that secure the
cable.
See if this helps.
Max
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Re: MH-36D Microphone puzzle
Hi Greg,
Not sure if you have tried this but it has worked for me in the past.
Take the mic connector apart and solder a bare 2" or so length of wire to pin 7. Route the other end of the wire back through the mic plug and wrap it around one of the screws that secure the cable.
See if this helps.
Max
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Re: MH-36D Microphone puzzle
A quick update...
I'm now thinking the problem has nothing to do with C104.? I tried inserting a capacitor in series with the mike line (pin 8 on the round connector), and the problem remains unchanged.? Further, I can make the problem dramatically worse by simply holding the top portion of the microphone (around where the mike holes are) against my face.? AC hum pick-up.? Holding the mike by the cord at its base, and using the MoX button on the radio, there is no hum.? So, it's like there's a lifted ground somewhere, but I can't find it.? Poking around inside the mike with a straight pin or needle held in my fingers, I can touch any of the ground traces and the hum disappears.? The schematic I found turns out to not match the MH-36D exactly - parts layout slightly different, some different parts - so this level of troubleshooting will be challenging.? It's for the MH-36A6J.? Does anyone know of a proper MH-36D schematic?
Perhaps unrelated, I notice that the mike volume control on the radio does not seem to have any effect on either the hum or the volume of my voice when in FM mode.? It does work in both SSB and AM mode, and functions the same with either microphone model.? Is that expected?? Just trying to rule out a rig problem as perhaps compounding the troubleshooting effort.
I opened up the MH-1B8 microphone that I have been using (with no hum), and see that it uses a shielded cable between rig and mike, with the shield connected to the "Mike GND" pin 7 on the round connector, and that goes to the ground side of the microphone element itself.? The other ground pin 5 on the connector is used for the up / down / fast buttons, with the two grounds only connected inside the 847.? Since the MH-36 microphone only has a single ground pin internal to the mike, and uses an unshielded cable, I'm presuming it should be connected to the Mike GND, not the other one.? Connecting it to both 5 & 7 didn't help; I haven't tried 5-only, as that doesn't make sense.? Yes?
I've got one of the cheap knock-off MH-48A6J mikes on order, since it uses the same replacement cable as the MH-36.? Hoping it will function with the 847.? Plan is to swap mikes on my cable that has the round connector spliced in, and see if the hum is fixed.? If it works, I'm done.? If not, it was a cheap troubleshooting tool.
Greg? KO6TH
Greg D wrote:
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Right, pin 8 is mike, and pins 5 & 7 are the grounds.
So, leaving pin 5 unconnected seems to have helped a bit, but there's still a hum.? After some troubleshooting on the local repeater, we noticed that placing my hand on the transceiver itself while transmitting (holding the mike) made the hum go away, indicating a capacitive problem somewhere.? Bridging an extra decoupling cap across the power internal to the mike didn't change anything, however.
The new theory is that the problem might be a shorted cap in the microphone line (pin 8).? Guessing C104, according to That would explain the high voice volume, as well as perhaps the hum.
I'm measuring about 28k ohms across it (in-circuit), with the probes in either polarity.? So, it's not shorted, but perhaps really leaky?
Before digging in (it's a more invasive fix for me), does that sound plausible?
Thanks for the help!
Greg? KO6TH
Omni wrote:
I think you have the mic wired wrong. Pin-8 is the mic input not ground, which would explain the hum. Also, do not tie the mic ground (Pin-7) and the "other" ground (Pin-5) together.? They are separated for a reason, so keep them that way.? The POT controls the DTMF signal level and I would not suggest messing with it.
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Re: MH-36D Microphone puzzle
Hi Andrew,
Looking at the schematic (if this is correct:?
),
I don't see one.? Where would it be?
Greg? KO6TH
Andrew Lenton wrote:
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Make sure there is a 560 ohm resistor across the
mic!
BR
Andrew
Get
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Re: MH-36D Microphone puzzle
Right, pin 8 is mike, and pins 5 & 7 are the grounds.
So, leaving pin 5 unconnected seems to have helped a bit, but there's still a hum.? After some troubleshooting on the local repeater, we noticed that placing my hand on the transceiver itself while transmitting (holding the mike) made the hum go away, indicating a capacitive problem somewhere.? Bridging an extra decoupling cap across the power internal to the mike didn't change anything, however.
The new theory is that the problem might be a shorted cap in the microphone line (pin 8).? Guessing C104, according to That would explain the high voice volume, as well as perhaps the hum.
I'm measuring about 28k ohms across it (in-circuit), with the probes in either polarity.? So, it's not shorted, but perhaps really leaky?
Before digging in (it's a more invasive fix for me), does that sound plausible?
Thanks for the help!
Greg? KO6TH
Omni wrote:
toggle quoted message
Show quoted text
I think you have the mic wired wrong. Pin-8 is the mic input not ground, which would explain the hum. Also, do not tie the mic ground (Pin-7) and the "other" ground (Pin-5) together. They are separated for a reason, so keep them that way. The POT controls the DTMF signal level and I would not suggest messing with it.
|
Re: MH-36D Microphone puzzle
Make sure there is a 560 ohm resistor across the mic!
BR
Andrew
Get
|
Re: MH-36D Microphone puzzle
I think you have the mic wired wrong. Pin-8 is the mic input not ground, which would explain the hum. Also, do not tie the mic ground (Pin-7) and the "other" ground (Pin-5) together. They are separated for a reason, so keep them that way. The POT controls the DTMF signal level and I would not suggest messing with it.
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of Greg D Sent: Friday, August 26, 2022 1:22 PM To: [email protected]Subject: [YaesuFT847] MH-36D Microphone puzzle Hi folks, I've been using an MH1-B8 microphone for a while (few years), substituting for the rig's original MH-36D which had the disintegrating rubber cord problem. Following up on recent suggestion on the Amsat forum, I ordered and received a replacement cord meant for the MH-36 with the RJ plug. Cut off the RJ and connected the 8-pin round connector, and it seems to work, including the DTMF keys which is why I wanted to do the repair. But, I'm getting reports that my audio has a sort of hum on it, and the volume is rather hot, even with the microphone gain turned all the way down. I double checked the wiring, and I think it's right. The new cable has 6 wires instead of 7, so left the missing "Fast" line unconnected on the 8-pin. The MH-36D has no such button, so no loss there. The 2 grounds (mike and other) are connected together at the 8-pin connector; there's no "shield" on the cable, nor was there one on the original. Is this behavior - the hum and loudness - "expected", or is there something else going on? I see what appears to be a small potentiometer inside the mike, just above the connector. Does that need to be adjusted? What is it for? I haven't touched it as yet, but I'm not the radio's original owner. Thanks, Greg KO6TH
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Hi folks,
I've been using an MH1-B8 microphone for a while (few years), substituting for the rig's original MH-36D which had the disintegrating rubber cord problem.? Following up on recent suggestion on the Amsat forum, I ordered and received a replacement cord meant for the MH-36 with the RJ plug.? Cut off the RJ and connected the 8-pin round connector, and it seems to work, including the DTMF keys which is why I wanted to do the repair.
But, I'm getting reports that my audio has a sort of hum on it, and the volume is rather hot, even with the microphone gain turned all the way down.? I double checked the wiring, and I think it's right. The new cable has 6 wires instead of 7, so left the missing "Fast" line unconnected on the 8-pin.? The MH-36D has no such button, so no loss there.? The 2 grounds (mike and other) are connected together at the 8-pin connector; there's no "shield" on the cable, nor was there one on the original.
Is this behavior - the hum and loudness - "expected", or is there something else going on?? I see what appears to be a small potentiometer inside the mike, just above the connector.? Does that need to be adjusted?? What is it for?? I haven't touched it as yet, but I'm not the radio's original owner.
Thanks,
Greg KO6TH
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Andrew Lenton
Bill
Andy Bosworth
Richard
Spence G5STO