Good morning Sirs,
first of all sorry for the English language: I'm Italian and unfortunately I don't speak German.....I've read this interesting thread thanks to Google Translator
The job performed on this Offenbach is amazing, so I would share with you my troubles with another sample of Offenbach U53 (a friend brought it to me to overhaul).
Really this radio has already been repaired in the past (changing electrolytics, paper capacitors and same resistors), but my friend told me: "it worked for a little time, than...only hum in FM and something (but wrong) in AM".
From the first check, the voltages on the tubes are OK (approximately 90V on the plates and 70V on the screens) and the tubes are in good condition (tested on my Unaohm GB24 for emission and mutual conductance).
Next step was to check the FM intermediate frequency chain, by injecting a 10,7 MHz signal on the first grid of the first DF91......but the bad surprise was that the signal dies along the way, despite the capacitive trimmers on the filters are adjusted for the maximum (and the tubes and the 5nF "pill" capacitors are good). You can see the situation in the image below (Vpp is for "peak to peak", because I checked the signal step by step with the oscilloscope):
I've a doubt about the working state of the capacitive trimmers.....could someone tell me what's the capacitive range that they have to realize?
But this radio seems a never-ending challenge.............my friend told me that the serviceman (that repaired the radio in the past) had to work a lot on the sliding contacts of the band selector. So I got so brave, removed the two screws on the chassis and moved the band selector to perform some checks.................and I had a terrible surprise:
With the method described by Toni I removed the sliders and now the mechanics is on the table: I'm going to reproduce (in a manner that I have to imagine) the plastic part that move the slider.
It's sure that this damage is not the cause for the wrong signal on the intermediate frequency chain.....but it's also true that in this condition the radio cannot work!
Any advice about this radio will be very appreciated!
Greetings from Roberto (Genova, North of Italy)
first of all sorry for the English language: I'm Italian and unfortunately I don't speak German.....I've read this interesting thread thanks to Google Translator
The job performed on this Offenbach is amazing, so I would share with you my troubles with another sample of Offenbach U53 (a friend brought it to me to overhaul).
Really this radio has already been repaired in the past (changing electrolytics, paper capacitors and same resistors), but my friend told me: "it worked for a little time, than...only hum in FM and something (but wrong) in AM".
From the first check, the voltages on the tubes are OK (approximately 90V on the plates and 70V on the screens) and the tubes are in good condition (tested on my Unaohm GB24 for emission and mutual conductance).
Next step was to check the FM intermediate frequency chain, by injecting a 10,7 MHz signal on the first grid of the first DF91......but the bad surprise was that the signal dies along the way, despite the capacitive trimmers on the filters are adjusted for the maximum (and the tubes and the 5nF "pill" capacitors are good). You can see the situation in the image below (Vpp is for "peak to peak", because I checked the signal step by step with the oscilloscope):
I've a doubt about the working state of the capacitive trimmers.....could someone tell me what's the capacitive range that they have to realize?
But this radio seems a never-ending challenge.............my friend told me that the serviceman (that repaired the radio in the past) had to work a lot on the sliding contacts of the band selector. So I got so brave, removed the two screws on the chassis and moved the band selector to perform some checks.................and I had a terrible surprise:
With the method described by Toni I removed the sliders and now the mechanics is on the table: I'm going to reproduce (in a manner that I have to imagine) the plastic part that move the slider.
It's sure that this damage is not the cause for the wrong signal on the intermediate frequency chain.....but it's also true that in this condition the radio cannot work!
Any advice about this radio will be very appreciated!
Greetings from Roberto (Genova, North of Italy)
