Hello Everyone,

I had that pocket radio for a long time, and now I had some time to look at it. It does not work, no surprise there.

Here is some info on it at the radiomuseum web site: http://www.radiomuseum.org/r/philips_90al071_90_al_071.html
On Beka's web site there is a pictorial of its dis-assembly and some documentation on it: http://translate.google.com/translate?hl=en&sl=auto&tl=en&u=http%3A%2F%2Foldradio.tesla.hu%2Fszetszedtem%2F569philips-zsebradio%2Fal071.htm

The oscillator is not working in my radio.
Here is a pic of the front end schematics of the radio. (I expanded the schematics from Beka's web site.) +2 gets +3V through a 220 Ohm resistor and 47u bypass cap. I also added a 10n cap there.

This is what I have looked at so far:

- DC voltages are in the ballpark.
- Resistors have the proper values.
- Transistor is fine, has a beta of 295.
- Disconnecting L1 and driving it from a signal generator the circuit peaks at the right frequency and with reasonable Q.
- At the osc coil the tap was not connected, dismantled the coil and reconnected it. Just needed a touch up at the solder lug. Now there is signal at the tap point.
- Paralleled C2 with another 10n cap.
- Grounded the base of Q1 with a 10n cap (the osc works in a grounded base configuration).
- Sometimes, at parts of the frequency band, when I grabbed the ferrite bar of the loop stick antenna, as if I have seen the stage oscillating! I have not checked the frequency though. Most curious!

Well, it is still not oscillating!

Only thing I can think of is that the phase of the osc coil is reversed (no positive feedback). It is highly unlikely, as the radio certainly looks used, so at one stage it probably did work and the coil looked original!
I also simulated the circuit and it does not seem to be too sensitive for component/feedback variations.

I would love to hear theories that what could be wrong!

Thanks, Peter

Hello Peter,

Is the cap at left of T2, the 1st IF transformer, internal ?

If so, have seen these fail & cause odd symptoms. On some of the older ones, the silver-mica wafer is simply connected by a small spring tab in base which can lose contact... Try parallelling the cap on primary winding pins with a 0-365 pF variable and slowly adjust it through range while monitoring the oscillator... Just an idea since it appears you've already been pretty thorough in checking the convertor circuit...

Good luck & let us know !
John

Hi Peter,

That radio isn't particularly valuable. Worth about $5 - $10 depending on condition.
Not sure if it's worth the trouble to repair, but that's your choice. If you're doing it for fun, then thats OK.
One just sold recently on eBay for about $8.50, see here:
http://www.ebay.com/itm/ws/eBayISAPI.dl ... true&rt=nc

Your radio seems to be targeted for the European market, so you probably won't see much information
on this side of the pond. In fact Sam's Photofacts show absolutely no Phillips radios in the TSM series.

All that being said, I wonder if you have an intermittent connection at the antenna or around the oscillator circuit?
I'd reflow all the solder connections in that area, cleanup with 90% isopropanol alcohol and check with a 8X loupe.
Good luck.

~ Mitch ~

Hello Everyone,

Yes, I am doing this radio for fun!

Did some more checking, and it looks like the osc coil is not up to snuff. Took it out again, and put it on the Q-meter. At 1MHz Q is 40, at 1.3MHz the Q is only 30. There is probably some internal short in it. It has that lovely green and red wires with the thermoplastic insulation. I will probably rewind it with some properly insulated wire.

Peter

If you have a scope do a ringing test on the osc. coil --this will tell you for sure.

If the coil is fine then replace the transistor irregardless of how it tests. I have had literally hundreds of sold state radios, particularly auto radios, that had osc. transistors that checked fine but would not oscillate. Remember murphy ----Amplifiers oscillate and oscillators amplify.

You might find a bit more information if you search for a Philips 90RL071:
http://www.google.com/search?q=90RL071& ... h=577&bs=1

~ Mitch ~