Alinco VHF DR-135

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Werthers
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Alinco VHF DR-135

Post by Werthers »

Not happy.... I guess happens at some point, I was quite fond of this radio and used it a lot for 2 meters but today I found that the receiver has gone deaf.

It transmits perfectly fine and people can hear me but I can barely hear them and when I had it on Air Band today I was picking up nothing at all. I checked the antenna system and all is well and tested with another radio and things were all good so my Alinco has developed a fault with the receiver.

Is this easily repairable, I haven't opened the radio yet. Is this a common fault on these radios? Tbh I wouldn't know what to check for on the receiver section.
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Re: Alinco VHF DR-135

Post by wa10 »

I had a DR599t dual bander years ago that went deaf as if somebody turned the RF gain way down, what would be end scale dropped to about s2-s3

Checking the front end as far as the first mixer is not the source of attenuation is doable with no test gear if you can follow the circuit description schematic & board layout in the 135 service manual,

Before I got a sig gen I traced faults like this by using a multimeter lead as a probe/antenna to listen to a second radio while I probed along the front end watching signal strength looking for anywhere the signal jumps up notably between antenna socket & first rf amp,
& to make sure the rf amp is amplifying by the drop in signal when you probe after the rf amplifier effectively bypassing it,

if its transmitting as normal the antenna low pass filter is likely ok & your problem is after L111 on the main unit where the rx samples what's coming through the low pass filter,

check the diodes D109 108 & 107

before & after rf amp Q107 you have varactor tuned filters that get tracking voltage from the vco,

If the tracking voltage is missing or Q107 has lost its supply it will be low on rx or deaf,


I used the same method in reverse for transmitter fault finding, probing the tx strip from tx mixer to pa final transistor while watching a receiver,
no scope needed,

Discharge yourself of any static electricity before you start poking around near fets, been in circuit does not make them immune to death by static.
W8JI
"An antenna with a poor ground using few radials cannot have a support mast grounded to the radial common point (at least it shouldn't if designed properly) There is no exception to this!
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Werthers
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Re: Alinco VHF DR-135

Post by Werthers »

Thanks for all the info :thumbup:

I actually paid very little for this radio less than ten pounds and I thought I got a right bargin, besides it did work well for a while. After removing the cover I can see why I got it cheap. Its been modified by who ever owned it before me.
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Re: Alinco VHF DR-135

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Re: Alinco VHF DR-135

Post by wa10 »

The little board looks to be connected to c177, its part of the front end filter for the air band rf amplifier Q112,
double diode D107 switches which rf amplifier & filter is used,

looks like there are only chokes & caps on the board so its likely an added filter for air band, maybe to stop commercial FM radio stomping on your airbus A300.
W8JI
"An antenna with a poor ground using few radials cannot have a support mast grounded to the radial common point (at least it shouldn't if designed properly) There is no exception to this!
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Re: Alinco VHF DR-135

Post by Werthers »

I'll do some fault finding with the multi meter. I'm going to check for simple things first.
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Re: Alinco VHF DR-135

Post by wa10 »

If its not working you have nothing to lose by having a poke around,
Good luck
W8JI
"An antenna with a poor ground using few radials cannot have a support mast grounded to the radial common point (at least it shouldn't if designed properly) There is no exception to this!
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Re: Alinco VHF DR-135

Post by theEarwigger »

Recently I know someone with an Alinco DR635 that failed the same way.
Deaf on VHF.

The circuit is more like a handheld with huge gain and a weedy mixer that gets swamped by anything from airband to pagers. That maybe why that DR135 was modded.

I believe the fault was a PIN diode. The parts are available from Mouser UK but unles you are confident in soldering small parts get someone else to do it.

73, Rob.
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Re: Alinco VHF DR-135

Post by Werthers »

theEarwigger wrote: 11 Apr 2021, 14:16 Recently I know someone with an Alinco DR635 that failed the same way.
Deaf on VHF.

The circuit is more like a handheld with huge gain and a weedy mixer that gets swamped by anything from airband to pagers. That maybe why that DR135 was modded.

I believe the fault was a PIN diode. The parts are available from Mouser UK but unles you are confident in soldering small parts get someone else to do it.

73, Rob.
Wow excellent I got it working. I was doubtful but I thought what the hell, changed out the PIN diode and its receiving again.
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Re: Alinco VHF DR-135

Post by wa10 »

:clap: good result , that makes you a rig doctor
W8JI
"An antenna with a poor ground using few radials cannot have a support mast grounded to the radial common point (at least it shouldn't if designed properly) There is no exception to this!
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Re: Alinco VHF DR-135

Post by Werthers »

wa10 wrote: 27 Apr 2021, 19:06 :clap: good result , that makes you a rig doctor
Not quite a rig doctor yet but have repaired other electronic stuff.
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