Author Topic: Yaesu FT-101 - Hoping to fix.  (Read 56 times)

0 Members and 1 Guest are viewing this topic.

Offline mael

  • Newbie
  • *
  • Posts: 10
  • Karma: +0/-0
    • View Profile
Yaesu FT-101 - Hoping to fix.
« on: October 06, 2017, 03:19:00 PM »
I just want to receive on it.  I don't intend to transmit with it.  I posted a bit about it in the 'introductions' forum.  Now I've migrated here hoping to  get some advice and and learn ways to get the thing to work properly on receive.

It was given to me by someone who used to use it but I'd say by the look of it and clues in what he said, that it hadn't been fired-up for a decade and maybe two!

I kinda like listening to SW, and it's one way of finding something in English.  I live on a small island in Japan and English is hard to come by. I use a few radios to try to find something rather than the local stuff, but I thought the Yaesu must be better at it.  And it was!  For two days it was quite fun to use.  Then I noticed the volume and/or sensitivity was becoming weaker, and after another day or so it only picked up the odd squeak with indecypherable speech mingled therein.

This post was something I intended to do tonight, but I got side-tracked for too long and it's time to sleep - so I'm not going to do much at the moment except begin this thread.
I downloaded the instruction manual, and a short while ago I separated it into sections.  It's huge!  Some 221 pages.

The FT-101 that adopted me is pretty early I'd say.  I've seen a few Youtube vids about the FT-101 and none of them has actual transistors in the speaker output board that I saw.  Well that's the age of the thing I've got.  It has two large heatsinked transistors with what must be thermistors neatly glued on top.

I shall now try to abandon the introductory thread I started and try to work it out here. 

I'm not an expert with electronics, but I can basically navigate my way around a circuit board and I'm no stranger to fixing electronics and adapting them - allbeit on a pretty basic level.

I found that Yaesu had thoughtfully sealed the most dangerous voltage inside the box with the two output tubes.  But I discovered my forearm is quite capable of reaching a live part when I'm trying to check something else.

I'd love to get this going.  I intend to use this thread to speak of my progress, and also someone might have some great idea I can try.  Hopefully someone can say with confidence where I should start looking.

I've already changed a couple of cracked caps - but that didn't do it.  So I shall now try to digest the 221 page manual and follow what the author says.

Offline mael

  • Newbie
  • *
  • Posts: 10
  • Karma: +0/-0
    • View Profile
Re: Yaesu FT-101 - Hoping to fix.
« Reply #1 on: October 08, 2017, 04:26:13 AM »
I found PB1076.  That's the rec board.  Wow! It took half an hour to find it!  Next job is see if the voltage is within tolerance.  It's going to be a slow job at this rate.

One thing I always forget to mention is that the two power transistors on the audio board get really warm.  I assume they are for the speaker output.

Offline mael

  • Newbie
  • *
  • Posts: 10
  • Karma: +0/-0
    • View Profile
Re: Yaesu FT-101 - Hoping to fix.
« Reply #2 on: October 08, 2017, 02:34:15 PM »
The first step on the fault-diagnosis tree says to check the voltage on the rec board (1076B).  Well they are all quite a bit over 10% of spec.   Approaching 50% on a couple and 20% over on the 600V pin. I was using the earth on the board as the common.

So with that information I see I need to fix board 1076B as a first step - but I can't find anything in the service manual explaining how I might go about correcting the variance.  I assume the most likely components to go out of spec would be the caps.  So I suppose I should find some newer caps from my 'box-o'-circuit boards' and see if this sorts the problem out.

Though experience tells me things working at voltages well in excess of how they were intended can easily wreck semiconductors.  That worries me.

Yeah!  I'm obviously a bit slow at this.  I'm a bit out of my depth.  Though at least I can see some improvement in my knowledge of this beast.

Offline mael

  • Newbie
  • *
  • Posts: 10
  • Karma: +0/-0
    • View Profile
Re: Yaesu FT-101 - Hoping to fix.
« Reply #3 on: October 09, 2017, 06:56:19 AM »
Well.  One problem I have found is that the downloaded manual isn't the exact one for the model I've got.

I noticed mine uses power transistors on the output for the speaker but the manual I've got shows the circuit using an IC.

Also the rec board is not the one I've got a diagram of - though it's close.  I know I can find some info on the ones I've got on Youtube and here tho'.

Last night I observed that the aerial makes no difference.  It still picks up a few stations, but this is irrespective of whether or not the antenna is inserted.  I thought that was interesting.

Eventually I'll get some progress done.

Offline Bob KQ2Q

  • Newbie
  • *
  • Posts: 3
  • Karma: +0/-0
    • View Profile
Re: Yaesu FT-101 - Hoping to fix.
« Reply #4 on: October 12, 2017, 08:51:30 AM »
Hello Mael,

I read your Posts and would suggest that you locate a Manual and Schematic with Transistor Audio Output.
Let me know if you have a better schematic with a non-IC audio circuit.
If not, I will try to find something like that for you to use.

If there is no schematic, then I should be able to find a typical 2 transistor output, audio amp schematic. Most audio amps in the 3 to 5 watt range are reasonably similar.

We can then look at the DC Supply voltages at the Audio Amp.

My first thought is that the large capacitor between the Collector(s) and the Speaker is leaking. That will cause oscillation and squeal.

Keep me posted. I will assist where I can.
A picture of your audio amp board would help also

-Bob KQ2Q  Danielsville, GA