Roberts old r200 (radio).

[Sea Chief]

Hi chaps. Would anyone know anything about 60's UK radios? My lovely old r200 roberts, seems to be faulty ( very tiny squeak of volume, tried two new block batteries/ same, lack of volume).

Can't think where else to ask. Thanks, Sea Chief

[vintagekiki]

http://www.radiomuseum.co.uk/R200/R200v2.pdf

https://www.vintage-radio.com/recent-repairs/roberts-r200.html

https://www.youtube.com/results?search_query=RS+Roberts+R200+Electrical+repairs

https://www.youtube.com/watch?v=YQqAiL6fI6Y
Roberts R200 part 1

[mozz]

Look up AF117 and the tin whisker problems.

[pdf64]

Look up AF117 and the tin whisker problems.

Cheap Soviet equivalents mentioned here https://www.radiomuseum.org/forum/su...ansistors.html

[vintagekiki]

To help

First Book of Transistor Equivalents
Second Book of Transistor Equivalents
International Transistor Equivalents Guide

[Sea Chief]

http://www.radiomuseum.co.uk/R200/R200v2.pdf

https://www.vintage-radio.com/recent-repairs/roberts-r200.html

https://www.youtube.com/results?search_query=RS+Roberts+R200+Electrical+repairs

https://www.youtube.com/watch?v=YQqAiL6fI6Y
Roberts R200 part 1

Hi vkk.. very useful links, thanks for these.

It seems like AF117 transistors might seem like the 1st port of call to check.. but with only a DMM?

[Sea Chief]

Look up AF117 and the tin whisker problems.

Hi mozz.. yes this seems like the place most often queried 1st from vkk's links in the post before. But how to test my AF117's.

Tin whiskers ?

[Sea Chief]

Cheap Soviet equivalents mentioned here https://www.radiomuseum.org/forum/su...ansistors.html

Thats another very useful link pdf.. thanks.

I wonder if the sensible thing might be to just replace the 3x I think, Af117 transistors, with some cheap russian equivalents. It doesn't warrant buying transistor testers, its only an old ebay r200.. but very dear to me though even if it was £10, 15 yrs ago!

[Sea Chief]

Anyone know what 'zapping' means in the context of these transistors?

[vintagekiki]

About AF117

https://www.vintage-radio.net/forum/showthread.php?t=180298
Zapping AF117 transistors

https://www.vintage-radio.com/repair-restore-information/transistor_transistor-faults.html
Transistor Faults, Testing and Replacement

https://www.vintage-radio.net/forum/showthread.php?t=76440
AF11x transistors, 'tin whisker' problems and solutions.

https://www.vintage-radio.net/forum/showthread.php?t=153180
Testing an AF117 transistor

https://www.youtube.com/watch?v=xFwDXIYgBvQ
Tin whiskers inside a AF117 transistor.

https://www.radios-tv.co.uk/community/components/af117-tin-whiskers/
AF117 Tin whiskers.

https://www.vintage-radio.net/forum/showthread.php?t=18701
AF117 replacements

1)
https://www.google.com/search?q=roberts+radio+r200+repair
roberts radio r200 repair

[vintagekiki]

It seems like AF117 transistors might seem like the 1st port of call to check.. but with only a DMM?

The tiny, squeak, distorted sound at old radios is mainly due to dried filters and coupled electrolytic capacitors. As a rule, before any intervention, it is desirable to replace them.
If the fault has not been rectified after replace, check the operating points (Ube) of the transistor.
When testing transistors, the fastest method is to measure the gain (hfe) on a DMM

Testing a transistor with an analogue multimeter
https://www.radio-electronics.com/info/t_and_m/analogue-multimeter-voa-vom/testing-diode-transistor-with-multimeter.php
https://www.instructables.com/id/How-to-test-Bipolar-Transistors-if-you-have-an-Ana/
https://www.mikroe.com/ebooks/components-of-electronic-devices/diodes-and-transistors
http://120studio.com/tech/transistors.htm

Simple transistor testers
https://www.elprocus.com/simple-transistor-tester-circuit/
http://www.talkingelectronics.com/projects/50%20-%20555%20Circuits/images/TransistorTester.gif
https://electronicsforu.com/electronics-projects/hardware-diy/easy-transistor-tester

[pdf64]

Anyone know what 'zapping' means in the context of these transistors?

Tin whiskers cause a problem by shorting things together. My guess is that zapping means identifying the short, and feeding a current source through it, oriented to be reverse biased. The voltage would need to be limited to well below the reverse biased junction voltage limit. Just randomly connecting a battery across the tin whisker short might get rid them but in the next instant, blow the transistor.
But even if successful, there may be other tin whiskers in waiting.

But as per previous post, there’s no indication that tin whiskers are the issue here, it’s not as if a shorted AF117 has been identified.

What’s the problem with operating the transistor with its problematic metal can removed?
To avoid it becoming an optotransistor, it would need isolating from light somehow. But inside a radio, would its exposed gubbins become liable to damage from environmental contaminants?

I have a background in the UK rail sector, where tin whiskers are a major issue, following a post disaster investigation finding that they were to blame for the signalling failure that caused it.
It’s pretty difficult for designer to be sure that a system is ‘fail safe’, if any circuit node can randomly short to any other!
Due to the issue from tin whiskers in lead free solder, key industry sectors such as aerospace, transport, nuclear and military have an exemption under the lead free regs.

[Helmholtz]

I think the method means burning off (melting) the shorting tin whiskers by a strong short-circuit current (discharging an ecap).

[vintagekiki]

Question
Is it whisker or whistler like radio noise. Nearby lightning sounds like the familiar crackle heard on an ordinary AM radio but distant lightning produces distinctive `chirps. `

https://en.wikipedia.org/wiki/Whistler_(radio)

[Helmholtz]

Question
Is it whisker or whistler like radio noise. Nearby lightning sounds like the familiar crackle heard on an ordinary AM radio but distant lightning produces distinctive `chirps. `

https://en.wikipedia.org/wiki/Whistler_(radio)

It's whiskers and means very thin tin needles, which spontaneously grow over time and may cause shorts.