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Old 2nd Oct 2011, 3:04 pm   #1
G4GNU Andy
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Default Roberts R200 schematic

Help please! I have acquired an early R200 (s/n 9896) and it is dead! The first thing I noticed on taking apart is that the waveband switch was very loose and had obviously been turned round a few times, twisting the wires and causing 3 to come adrift! I have no circuit diagram or schematic or anything that would tell me where to re-connect the wires that have come away (pink from tuning cap, orange from ferrite rod and black from pcb. Can anyone please help? Thanks in advance!
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Old 2nd Oct 2011, 3:08 pm   #2
Darren-UK
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Default Re: Roberts R200 schematic

http://www.service-data.com/section.php/7337/1

Note there's three versions of this radio but I'd assume the wiring in question was the same on all of them.
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Old 3rd Oct 2011, 9:44 am   #3
geofy
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Default Re: Roberts R200 schematic

http://www.vintage-radio.net/forum/s...ad.php?t=64700

The pictures in the link of my radio might help, this still has the AF117's fitted, I replaced one faulty one. One output transistor had gone faulty so both where replaced with AC128's and the bias current rechecked and set to around 5mA.
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Old 3rd Oct 2011, 1:17 pm   #4
G4GNU Andy
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Default Re: Roberts R200 schematic

Thanks Darren and Geoff, I found the link to the service manual but being tight, I just wanted to replace the fallen off wires first to see if that did the trick, if not then I will definitely invest in the service manual. Your photo (rb2.jpg) would have helped Geoff, but the model I have has a rotary switch with 4 inner (poles) that can each switch to 3 separate positions. This is from memory as I am at work and the radio is at home! If anyone can just give me the wiring detail of this switch (or a photo) that would be great. Thanks again!

I was told the radio was working but that was obviously before the wavechange switch came loose and was swivelled round several times! This is why I am hopeful that just re-soldering these 3 wires back on will do the trick.
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Old 3rd Oct 2011, 9:40 pm   #5
G4GNU Andy
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Default Re: Roberts R200 schematic

Have purchased the service sheet and have reconnected all wires. Sort of works when I hold the ferrite aerial. At least the audio side is fine! Thanks for your help, much appreciated.
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Old 8th Oct 2011, 5:16 pm   #6
See_Mos
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Default Re: Roberts R200 schematic

I have just repaired one of these, The detector diode inside the last IF can was open circuit. An oscilloscope showed plenty of signal at the last AF117 collector but nothing at the volume control. I replace the diode with an OA91.
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Old 19th Nov 2011, 3:26 pm   #7
Neil Purling
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Default Re: Roberts R200 schematic

How do you get on locating component positions on the print side of the PCB to remove them. I don't know if Newnes has the component positions marked onto a diagram of the PCB tracks for the three versions or not.
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Old 20th Nov 2011, 10:30 am   #8
geofy
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Post Re: Roberts R200 schematic

Quote:
Originally Posted by G4GNU Andy View Post
Have purchased the service sheet and have reconnected all wires. Sort of works when I hold the ferrite aerial. At least the audio side is fine! Thanks for your help, much appreciated.
If there is a radio signal when the ferrite is held, it could be a coupling capacitor or the tuner has not been connected correctly, holding the aerial is making a capacitive coupling.

Quote:
Originally Posted by Neil Purling View Post
How do you get on locating component positions on the print side of the PCB to remove them. I don't know if Newnes has the component positions marked onto a diagram of the PCB tracks for the three versions or not.
If there are any spare holes in the board, put a bit of single strand wire though the hole, it gives some idea of where the top of the board is in relation to the other side. Then look at the transistor and figure out where the leads are attached to the printed side, it shouldn’t be to difficult. Find the connections to the output transformer as the leads will be close to this.
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