Do you have a Roberts Revival R250 radio with only hiss on some wavebands? It’s a fairly common problem with these radios caused most likely by a batch of faulty components or rough handling.
Warning – this gets technical but it’s really not difficult and you can have your radio working again in an hour or so.
All you need is a voltmeter, soldering iron and some spare parts and it’s a fairly easy fix.
If the AM wavebands just hisses and no station can be tuned in on MW or LW there are several likely causes. To find out which follow the checks below.
Cause 1: Broken aerial wires / set rattles – the internal ferrite rod aerial has two sets of coils one for MW and one for LW. The wires are fine and there are four wires for each waveband. Unfortunately the studs and glue that hold the ferrite in place can break and the rod becomes detached and rattles around inside. If you have bought a radio from eBay and had it shipped by MyHermes then this is the likely problem (I’ve had several damaged this way by MyHermes and don’t mind publishing the fact although of course other couriers may be just as bad. I’ve seen the MyHermes lorry throwing sacks of parcels out onto the road in the early morning for the local drivers to pick up and scurry away into their cars and vans.) Parcels are subjected to excessive g-force and the high mass aerial suffers. Best just send it back as eBay covers buyers. But if you have a broken aerial read on.
It’s possible to re-solder the wire if it’s not broken right next to the coil. Don’t try to strip back the insulation, just heat each wire end with the soldering iron and the insulation should dissolve so that a solder joint can be made. The wires are colour coded so if several are broken it may take some detective work to figure out which goes where. The circuit board has cryptic lettering to help – MG – medium wave green, LB – long wave black. It’s likely the wires are still partly in place so you can see where they connect to the board. If the ferrite itself is broken it can be super glued together but best use an elastic adhesive to fix the whole aerial back into the clips.
Cause 2 – Oxidised wave change switch – this can affect FM as well but mostly shows up when switching to MW or LW due to more contacts in use. The problem is crackle when changing bands and sound may return if the button is held pressed down repeatedly. The fix is a squirt of switch cleaner – pop into Maplin and pick up an aerosol contact cleaner ideally with lubricant. Apply a little to the top of each switch in turn while pressing the button up and down to clean the contacts. The hiss should disappear and wave change return to normal. It may take several goes to clear the problem. If there’s rust showing around the switch housing it’s likely the radio has been exposed to moisture and may not recover. The switch assembly is interlinked with numerous connections that makes replacement (assuming you have one) only for the brave.
Ceramic capacitor suspect
Cause 3 – Faulty ceramic capacitors – the main chip controlling the AM/FM receiver is a BA4236L. It’s temping to think this is the problem particularly if the main audio chip has also blow (see Roberts R250 – No Sound Faults) when the problem lies in a cheap ceramic capacitor. Look for small buff coloured disc about 5mm diameter with the number 103. If you have an ohmmeter check to see if it’s low resistance it should of course show no reading. Replace with a 0.01uF (10nF) ceramic capacitor. There are two – C23 / C24 – the ones connected to pins 8 & 9 seem problematic.
Circuit diagram for Roberts R250 from http://vintage-radio.net
01/01/2018 at 5:19 pm
I am looking at fixing my mother’s old R250. Noisy and hissing on AM bands, with a loud tone (about 1 kHz) except at the strongest stations.
Cause 1: Nothing broken or loose
Cause 2: A lubricating contact leaner removed many of the noises, but it’s still not resolving AM stations.
Cause 3: I would like to confirm the capacitors you suggest, before I wield the soldering iron. C23/C24 are green and appear to be marked 2A103J (10 nF, 1000 V, polyester film caps). The ceramic caps nearby are 22 nF, 100 V (marked Z5U 223M). Which are the ones you consider most likely to give problems? And when checking the resistance, can they be checked in situ or do they have to be removed to avoid the influence of surrounding circuit components?
01/01/2018 at 9:17 pm
Hi Gerard – the 103 ceramic caps I had problems with are the circular light brown disks not the green polyester ones. When checking resistance it measured near 0 ohms in situ. I generally check for faulty components in situ and see if it measures the same resistance with multimeter polarity either way round but you are right that other circuit components could affect readings.
AM stations are becoming more difficult to tune in due to switched mode power supplies being used instead of the old transformer types. It’s worth checking the noise is still there on 9v battery power to rule out external interference.
25/10/2019 at 6:31 pm
I am repairing a Roberts R250 I found waiting disposal on top of a dustbin. I have found the posts here very helpful. Have you got the schematic for this radio? If so can I have a copy please.
26/10/2019 at 9:00 am
Hi Nick, I do have some circuit diagrams, will try to dig them out. You can also find the data sheets for the ICs that show example circuits that Roberts based their designs on.
26/10/2019 at 3:36 pm
Thanks. I have looked at the data sheets and have a very poor version of the schematic, missing parts and unreadable. If you have anything better I’d like a copy. You also mention using a contact cleaner from Maplin can you suggest an alternative now that it’s no longer available
26/10/2019 at 8:08 pm
Found an old schematic have added link to pdf in main post above, note sure if any better than one you have. There are some voltage readings from the IF chip that may help.
I use Servisol Super 10 switch cleaning lubricant. Hope that helps, let us know how you get on.
12/11/2019 at 10:54 pm
Thanks for schematic, it is the one I have though not as degraded. I wonder why it is so difficult to get official data on this model. I emailed Roberts but they never replied. So far I have replaced all the electrolytic caps and the ceramics mentioned above. I needed to replace the volume control as the switch no longer worked and the audio amplifier chip . Now I have a working radio with only hisses and whistles on LW/MW. Cleaning the switches removed all the crackling. FM works but the volume is about a half as loud as I would expect on full volume. Surprisingly it works just as well without the telescopic aerial. attached.
14/11/2019 at 10:51 pm
Good to hear you have made some progress. Had a few R250s with multiple faults like this. Check all the fine wires are connected on the ferrite aerial, they can break which causes the whistle and hiss. I’ve had the whole ferrite rattle around as the mounts have broken in transit and wires fractured. Low volume could simply be the headphone socket contacts tarnished – check how it sounds on headphones as it could also be a faulty speaker.FM often works without the aerial being extended but surprised signal does not improve when connected.
14/01/2022 at 8:35 pm
Hello there, I contacted you a while ago about no FM on my Roberts R250. I noticed when spraying the wave change switches that the MW switch will not go all the way down. All the others do and sometimes it even pops right out at the top. Also I can’t get LW. Could the problem with the MW switch cause it to stick on that one waveband at all? I do have a video.of this. I was that focused on the FM switch I didn’t notice that this MW doesn’t push all the way. Thanks for reading
16/01/2022 at 11:05 am
The plastic buttons do come loose and can jump out but should not affect the LW switching – check there’s nothing stuck in the mechanism that’s preventing the switch going fully down and locking. Lack of LW could be due to a broken wire on the ferrite aerial – follow each fine wires from the PCB to the coil and see if any have become detached. The LW coil has more turns and is thicker than the single layer MW coil. Hope this helps and you fixed the FM issue.