ICOM IC-251e

[g0hze snowy]

I have on the work bench the above radio, works fine on FM but fails on SSB, no tx.
All voltages appear present on the various connectors, which incidentally had been refitted incorrectly, took a while to identify the plocket ( plus and socket!) arrangements and correct, didn't help with the problem tho'.
I have a diagram but the various functions of each part of the circuit are not listed, i.e.: pll, vco, some like pa i can see.
Not having any formal training, i am just a hobbyist that has a reasonable amount of luck with repairs due to the many veterans on this site with help and advice.
Snowy

[g0hze snowy]

A closer visual inspection showed that R273 a 3k variable had disintegrated, wiper missing, this fed 1496 pin 1 of IC4, replaced it with a 4.7k, nearest preferred value, still nothing, will have to hook up my 2 tone osc to mic input, then i go hunting.

[Oldmadham]

Originally Posted by g0hze snowy

I have on the work bench the above radio, works fine on FM but fails on SSB, no tx.
All voltages appear present on the various connectors, which incidentally had been refitted incorrectly, took a while to identify the plocket ( plus and socket!) arrangements and correct, didn't help with the problem tho'.
I have a diagram but the various functions of each part of the circuit are not listed, i.e.: pll, vco, some like pa i can see.
Not having any formal training, i am just a hobbyist that has a reasonable amount of luck with repairs due to the many veterans on this site with help and advice.
Snowy

"plocket?" I really like that!

I like Icom gear, but it can be a real nightmare to dig through,
At the moment I have an IC575a with receive on F, but nothing on SSB, CW, or AM.
The transmit side had a fault earlier, with low power on all modes, which turned out to be a dry joint in the driver section of the PA section, so now it transmits OK on all modes, but the receive problem is recalcitrant.

They are complicated little sods of things, with, at least on the 575a, single sided boards, & wires making connections between various sections, plus the horrible little "TMP" coax connectors for the RF local osc, & IF connections between boards.
I have a IC251a tucked away somewhere, along with an IC245, both dead of unknown causes, & an IC490 with an "easy fix" if I ever get round to it.

Do you have an oscilloscope?
Unfortunately, my Tek 7613 failed just as I was starting to work on the IC575a, so I haven't been able to look at several of the LO signals.

The little 10MHz analogue 'scope I have that is still functional will still give a reduced display on 28MHz, & is useful for determining the presence or otherwise of the 9MHz IF.

A decent 100MHz analogue 'scope like the 7613 can help a lot, as it will see 146MHz reasonably well, so would probably do for the LO signals as well.
I'm not so sure about DSOs---some seem to have a bit of a "cliff-like" cut off.

Unfortunately, the 7613 is even harder to fix than the IC575a!.

I just looked up the IC251 schematic I have saved on this computer, but it is really cruddy.
The later Icoms have block diagrams in the manual, but I don't think the earlier ones do.
They still miss things out, but it does help to point you in the right direction.

[Oldmadham]

Your posting got me started Googling, as I'd like to have another try at fixing my IC251A, when & if I get the present beast sorted.
All of the schematics & most of the block diagrams were cruddy, but I finally found one site with the Instruction Manual that had a perfectly readable block diagram.
Having that tends to make it easier to "drill down into the schematic.

https://www.icomjapan.com/support/manual/2770/

[g0hze snowy]

Oldmadham, thanks for your input, yes i did find that and as you say, perfectly readable, the variable 'R' that i replaced is within the SSB circuit so that's item sorted, still another or more to go, the RIT light that will not switch off is one such fault. had my pm gonk, docs orders, after triple byepass so i will have another go at it once the tea has brewed, you know us brits like our tea, incidentally it was your countrymen on 110 and 111 battery in Malaysia that christened me 'snowy' in 1964, stuck ever since.

[Oldmadham]

Originally Posted by g0hze snowy

Oldmadham, thanks for your input, yes i did find that and as you say, perfectly readable, the variable 'R' that i replaced is within the SSB circuit so that's item sorted, still another or more to go, the RIT light that will not switch off is one such fault. had my pm gonk, docs orders, after triple byepass so i will have another go at it once the tea has brewed, you know us brits like our tea, incidentally it was your countrymen on 110 and 111 battery in Malaysia that christened me 'snowy' in 1964, stuck ever since.

G'Day, Snowy!

Yeah, these names do stick.
On my first day at the 6WF Broadcast site in 1965, the bloke who did the worksheets took one look at my initials & christened me "Bags".
I have been "Bags" ever since!

I currently have more dead radios than functional ones & will probably not be around long enough to fix them all.

My wife keeps telling me to buy some new stuff, but all the really new ham gear, except for the slightly dodgy stuff is too expensive.
Even secondhand things like IC706s, which you would expect to have come down to less stratospheric levels are still right up there!

Anyhow, I better sign off now, catch you later.
73, VK6ZGO