Bush TR190 - distorted audio - UK Vintage Radio Repair and Restoration Discussion Forum

Andy Green · 3rd Jul 2021, 11:28 pm

My wife's Aunt (who recently lost their husband) asked me if there was any way to convert her old Bush transistor radio to receive FM. This was a radio she had as a teenager in the 60's, and means a lot to her. So I volunteered to have a look, how hard could it be?

The first problem to fix is that the radio seemed to have pretty poor sensitivity, and the audio, such that it was, sounded quite distorted.

I have Paul's Data USB stick with the service information, so I set about trying to figure out the fault.

I didn't have a modulated sig gen to hand, only a standard audio sig gen, so I injected a sine wave into the wiper of the volume control, and looking at the waveform, it resembled a pretty good sine wave, and sounded like one too.

I then set about looking for likely looking capacitors to swap out, and I spotted some white corrosion around the one feeding the pot from the detector. Swapping it out, the audio distortion was pretty sorted, and I could tune in BBC R4 on LW, and BBC Radio Wales on MW (there's not much receivable on AM here in Ireland anymore in the daytime).

So I proceeded to build the I4CY kit:-

https://www.i4cy.com/m0oox/fm2am/

and fired it up. It seemed to work for a few minutes, but while experimenting with it, the Bush audio went back the way it was again, so after checking the battery voltage and taking the radio outside again to check R4 and BBC Wales, I packed up for the day.

Any common faulty components or tips on where to go next?

AC/HL · 4th Jul 2021, 12:34 am

Unless it's an Irish version, it appears to be a TR130. The mixer has been changed at some time, but the two IF transistors are AF117s, prone to tin whiskers, although that usually means dead!

vinrads · 4th Jul 2021, 9:29 am

It's worth checking the current consumption ,when the fault appears, try removing the output transistors from their heat sink, these can also suffer from tin whiskers.

Mick.

AC/HL · 4th Jul 2021, 12:18 pm

Yes. Traditionally OC81s were in a glass case in an aluminium tube, but those look to be later ones similar to the AC128 in a tinplated case.

3rd Jul 2021, 11:28 pm	#1
Andy Green Hexode Join Date: Jan 2005 Location: Waterford, Republic of Ireland Posts: 259	Bush TR190 - distorted audio My wife's Aunt (who recently lost their husband) asked me if there was any way to convert her old Bush transistor radio to receive FM. This was a radio she had as a teenager in the 60's, and means a lot to her. So I volunteered to have a look, how hard could it be? The first problem to fix is that the radio seemed to have pretty poor sensitivity, and the audio, such that it was, sounded quite distorted. I have Paul's Data USB stick with the service information, so I set about trying to figure out the fault. I didn't have a modulated sig gen to hand, only a standard audio sig gen, so I injected a sine wave into the wiper of the volume control, and looking at the waveform, it resembled a pretty good sine wave, and sounded like one too. I then set about looking for likely looking capacitors to swap out, and I spotted some white corrosion around the one feeding the pot from the detector. Swapping it out, the audio distortion was pretty sorted, and I could tune in BBC R4 on LW, and BBC Radio Wales on MW (there's not much receivable on AM here in Ireland anymore in the daytime). So I proceeded to build the I4CY kit:- https://www.i4cy.com/m0oox/fm2am/ and fired it up. It seemed to work for a few minutes, but while experimenting with it, the Bush audio went back the way it was again, so after checking the battery voltage and taking the radio outside again to check R4 and BBC Wales, I packed up for the day. Any common faulty components or tips on where to go next? Attached Thumbnails Last edited by Andy Green; 3rd Jul 2021 at 11:44 pm. Reason: add picture

4th Jul 2021, 12:34 am	#2
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Bush TR190 - distorted audio Unless it's an Irish version, it appears to be a TR130. The mixer has been changed at some time, but the two IF transistors are AF117s, prone to tin whiskers, although that usually means dead!

4th Jul 2021, 9:29 am	#3
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,766	Re: Bush TR190 - distorted audio It's worth checking the current consumption ,when the fault appears, try removing the output transistors from their heat sink, these can also suffer from tin whiskers. Mick.

4th Jul 2021, 12:18 pm	#4
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Bush TR190 - distorted audio Yes. Traditionally OC81s were in a glass case in an aluminium tube, but those look to be later ones similar to the AC128 in a tinplated case.