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Old 6th Aug 2018, 2:29 pm   #1
poppydog
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Default Roberts R500

I have a Roberts R500 with an intermittent MW switch. It has not responded to the copious amounts of Servisol I have put down it, once pressed a gentle sideways pressure restores MW. Has anybody ever had cause to remove one of these switchbanks for repair and if so any tips or solutions please as its something I am not looking forward to i.e. lifting foil etc.

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Old 7th Aug 2018, 8:58 am   #2
GeoffK
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Default Re: Roberts R500

If the MW switch is completely unsoldered so the tags are free and the switch can be moved around, a position might be found where the switch operates. Hold the switch in that position and resolder the tags. Or can the top be accessed with a small screwdriver blade to bend the contact slightly.
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Old 7th Aug 2018, 11:29 am   #3
poppydog
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Default Re: Roberts R500

Hello Geoff, all 3 switches are arranged to come out as 1 unit, accessibility inside the switch is not good. I am losing continuity on the pin in-between S3 and S5 and the pin in-between S9 and S7 on the sheet, reflowing makes no difference, I have got no choice but to remove and repair, being all mechanical should have a good chance of repairing it. I just don't relish the thought of bits of the solder foil coming unstuck upon removal

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Old 7th Aug 2018, 9:10 pm   #4
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Default Re: Roberts R500

I seem to have ended up in the s with this one. After an awful lot of dismantling the switch is out, however, there is a piece of what I think is solder trace laying on the board unattached. I am really hoping somebody has a scrap one they can look at for me as I cannot for the life of me work out where this solder trace has come from, if not this one is scrap. Please see pics.

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Poppydog
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Old 7th Aug 2018, 11:23 pm   #5
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Default Re: Roberts R500

Just seen this post, the correct method would be to completely remove pcb and
switch intact from the metal front panel first, and then desolder the switch. Difficulty is
caused by the double sided board. Inspect the board where the track has lifted,
such a lo tech circuit can easily use point to point wiring instead, see circuit diagram.

This is Roberts' first transistor with SW. My one has a Harrods sticker.
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Old 8th Aug 2018, 3:15 pm   #6
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Default Re: Roberts R500

This ones been scrapped, can the mods please close.
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Old 13th Aug 2018, 8:39 pm   #7
poppydog
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Default Re: Roberts R500

This one has been saved, as after all that the loose piece of solder trace hasn't come from this board. Poor quality control? After dismantling and cleaning the switch bank then reuniting the PCB with the chassis, its all working . There is however, a piece that I have just come across, some sort of retaining/hog ring, and don't know where its come from - any ideas?

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Old 13th Aug 2018, 9:31 pm   #8
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Default Re: Roberts R500

Looks like a clip from a volume pot.
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Old 14th Aug 2018, 7:23 pm   #9
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Default Re: Roberts R500

Thanks Oldtechfan, it is where its come from thanks, as I didn't remove it I had no idea. However, having to pull the shaft to alter the volume should have given me a clue, sometimes it takes a while to twig something that obvious, just thought it was a quirk of the radio.

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Old 16th Aug 2018, 7:56 pm   #10
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Default Re: Roberts R500

Some pics of the switch removed and under repair. The solder trace was very fragile, you can see there are bits trying to lift which was almost impossible to avoid.

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It was nice to be able to strip and clean the offending switch rather than replacing, which is what you would probably have had to do with something more modern. The solder flux during original assembly had run down the pins creating a varnish type of coating on them, servisol was useless at trying to remove this stuff, bit of fine paper sorted that and restored continuity.

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I managed to solder the switch back in with very little trouble, and was very pleased with the result as I had anticipated more lifting of the traces.

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I think if there ever was a next time around I would:

1. reunite the pcb to the chassis after soldering the wires from the ferrite, as trying to solder those wires onto the pcb up against the chassis was a real pain, avoiding the iron melting the insulation of the other wires was time consuming.

2. buy a new solder sucker so I didn’t have to keep going over the solder pins upon removal with the soldering iron.

3. maybe look at dismantling the switch without any unsoldering, its all held together with metal twists (practice on a turd ).

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Old 16th Aug 2018, 8:35 pm   #11
crackle
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Default Re: Roberts R500

This was mentioned in another thread, and it seemed quite reasonable price wise for a Temperature controlled de-soldering tool, so I just bought one.
It works well https://cpc.farnell.com/duratool/d00...st=desoldering

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Old 18th Aug 2018, 10:16 pm   #12
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Default Re: Roberts R500

Thanks for the link Mike but that's a bit too expensive for me just now.

The electrolytics in this radio were physically leaking i.e. powdery deposits on their tops, so I have decided to replace them, restuffing where I can. What I am hoping to do is to just plop the bored out caps over the top of the replacements that have been soldered in a position to do this, but I am not keen on hot melt glue as I have had little success with it, I thought about silicone sealant but I know that can be quite acidic. I was wondering if I could use a two part epoxy such as araldite 10min epoxy for this, it needs to be quick drying otherwise it will run everywhere and also gap filling to an extent.

Some pics of what I am trying to do below.

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Old 18th Aug 2018, 10:34 pm   #13
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Default Re: Roberts R500

Quote:
Originally Posted by poppydog View Post
I thought about silicone sealant but I know that can be quite acidic.
Hi.

Servisol used to do a good clear neutral cure silicone sealant which doesn't contain acetic acid so is safe to use on components. I have also used other makers' neutral cure silicone sealant available from many DIY outlets.

Good to see that you saved the R500, I have one in my collection which is yet to to be serviced.

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Symon.
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Old 20th Aug 2018, 10:12 pm   #14
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Default Re: Roberts R500

Hello Symon

Thanks for the advice on the silicone, I ended up using the ten minute epoxy and it did a very good job. A small dab on each cap and its held firm. However, I will consider using the silicone when the epoxy has gone.

And yes I am glad I saved it as well. The module has been removed, one of the AF117s was suffering from whiskers, both transistors were replaced with GT322bs. The pair of electrolytics inside the module were replaced as they were very bad.

Quite pleased at the way the restuffing has turned out, they are all slightly out of position but not too noticeable. All the electrolytics were replaced with good quality long life rubycons.

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Old 20th Aug 2018, 10:28 pm   #15
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Default Re: Roberts R500

Hi poppydog.

That's an excellent result and well worth the effort. I'll have to try this method on one of my next Roberts sets. It really does preserve the originality of the set which is more important in this case due to the chassis being quite visible to the user. In cases where the caps are out of sight then I would just use modern replacements.
Those Rubycon caps are very good quality like the similar Panasonic types.

Regards
Symon.
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Old 25th Aug 2018, 1:53 pm   #16
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Default Re: Roberts R500

Thanks for the encouragement Symon. The re-cap has made a massive difference to the sensitivity and sound. I just wish I had looked at the cabinet a bit more before I started as its worse that I thought, the rexine is coming off in sheets and it seems to have shrunk as well. I think its been stored in damp conditions, got to keep pressing on though as there has been far too much work done to leave it now
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