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-   -   Roberts R200 schematic (https://www.vintage-radio.net/forum/showthread.php?t=74734)

G4GNU Andy 2nd Oct 2011 3:04 pm

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!

Darren-UK 2nd Oct 2011 3:08 pm

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.

geofy 3rd Oct 2011 9:44 am

Re: Roberts R200 schematic
 
https://www.vintage-radio.net/forum/...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.

G4GNU Andy 3rd Oct 2011 1:17 pm

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.

G4GNU Andy 3rd Oct 2011 9:40 pm

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.

See_Mos 8th Oct 2011 5:16 pm

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.

Neil Purling 19th Nov 2011 4:26 pm

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.

geofy 20th Nov 2011 11:30 am

Re: Roberts R200 schematic
 
Quote:

Originally Posted by G4GNU Andy (Post 469618)
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 (Post 481547)
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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