My Latest Junker. Courier AM Car Radio.

[Radio Scotland]

Picked up cheap on ebay as a wee project, Courier AM Car radio, Tunes and seem's to receive well enough but the volume is quiet, Suspect electrolytic caps, Audio amp seem's to produce a loud buzz / crackle so confident it's working, According to radio museum it dates from 68, But uses modern silicon transistors and an IC Audio amp, The radio museum one is badged up as a radiomobile. I'd date it to the late 70s early 80s.

https://www.radiomuseum.org/r/radiomobil_75.html

[Mr 1936]

Hi

That audio amplifier IC looks suspiciously like the Plessey SL402/403 or badge-engineered Sinclair IC-10. I like the ingeneous braided thermal bridge from heatsink to case.

I remember those ICs from the late 1960's. They had enormous gain, and it was very hard to make them stable and avoid earth loop effects from circulating currents. A few minutes self oscillation at supersonic frequencies would send them into thermal destruction. The loss of hard earned pocket money somehow sticks in the memory......

More here: https://sound-au.com/articles/pwr-amp-dev.htm#s5a

[G6Tanuki]

I see Lockfit transistors. Known to suffer failures.

Also the blue-sleeved electrolytics can be problematic [I've had to replace a few in Pye Westminster two-way radios].

Car radios get to see a lot wider temperature-and-humidity ranges than domestic electronics, so parts that might last for 60 years in a domestic setting can be brought to failure in half that time when in a car.

[Radio Scotland]

Thanks for the info, Well judging by the replies it could well date to the late 60's, Wasn't aware silicon transistors and IC's Were that common back then.

[agardiner]

Interesting little set. Very compact.

[Radio Scotland]

Originally Posted by agardiner

Interesting little set. Very compact.

For the time period it is yeah,

Might use the pre-set button for a bluetooth conversion

[radioman]

This set is mid 70's : my brother had one and managed to blow up the audio IC which if I remember correctly was one of the TBA641 types. I was able to fix it with the correct IC but the radio is long gone now.

Andy

[Radio Scotland]

Originally Posted by radioman

This set is mid 70's : my brother had one and managed to blow up the audio IC which if I remember correctly was one of the TBA641 types. I was able to fix it with the correct IC but the radio is long gone now.

Andy

Cheers, That date seem's about right to me,

[60 oldjohn]

The centre of the PCB looks scorched, what has caused that?

John.

[Nickthedentist]

I can't see that (could be my eyes though!). Whereabouts exactly?

[Radio Scotland]

Originally Posted by 60 oldjohn

The centre of the PCB looks scorched, what has caused that?

John.

It's not scorched, I'm working on it now under a bright light and it looks ok,


One of the cap's is dated 73 so that ties in with radioman's date

[60 oldjohn]

Unconventional way of marking photo, but the mark I saw is under the paper clip. On the reverse side that area is distorted by the light. I hope you find it is just a faulty capacitor.

John.

[Radio Scotland]

Originally Posted by 60 oldjohn

Unconventional way of marking photo, but the mark I saw is under the paper clip. On the reverse side that area is distorted by the light. I hope you find it is just a faulty capacitor.

John.

See where you mean now, There's no damage in that area, Alas it isn't a capacitor issue as iv'e changed them all apart from the gold coloured 1000uf as that tested fine.


Still has a very low volume issue, Loud - ish buzz from the speaker when i touch the volume contacts,

Any idea's ?

[Radio Scotland]

Radio Fixed and sound's great, Was fixed ''by accident'' Anybody want to have a guess at what the problem was ?

[agardiner]

The gold coloured 1000uF?

[Radio Scotland]

Originally Posted by agardiner

The gold coloured 1000uF?

No cigar for you

HINT it wasn't a capacitor

[HamishBoxer]

Carbonised circuit board?

[Radio Scotland]

Originally Posted by HamishBoxer

Carbonised circuit board?

Look's like nobody want's my cigar's


Keep the guesses coming will reveal the answer at 10 pm

[HamishBoxer]

Last thought, braid earthing screw not tightened up enough?

[Radio Scotland]

Originally Posted by HamishBoxer

Last thought, braid earthing screw not tightened up enough?

Afraid not