Best way to repair bent Oscilloscope shafts? - Page 1
Forum section: electronics / repair

author: cmscss
author_rank: Newbie
timestamp: January 13, 2016, 01:33:59 am
content: Hi There,I recently received an Hitachi V-1100A analog oscilloscope with two bent shafts (H Position & VAR Holdoff).This is my first Oscilloscope (got it for a Guitar Amp project) so am VERY green when it comes to this stuff - I was wondering if anyone had suggestions for the best way to improve the bent shafts. The H Position in particular is difficult to turn because the shaft is bent - the VAR Holdoff looks angled because the front face holding the knob is bent (see side image for bent chassis) so the entire knob/pot is angled.I've powered the unit up and can see the calibration signal and the knobs work so would be keen to ensure the bent shafts don't cause damage when turned because of the odd angles.Any suggestions or pointers in the right direction would be much appreciated.Cheers

author: cmscss
author_rank: Newbie
timestamp: January 13, 2016, 06:26:14 am
content: OK, so I've taken the knobs and faceplate off and I'm pretty sure I don't want to bend the pots so am thinking I have to replace them.Does that sound like the best way forward? If so, it's bit daunting as I've only ever worked on guitar effects pedals, the service manual looks pretty full-on!Some questions...ConnectorsSee attached: [connectors.jpg] & [connectors-service-manual.png]I need to remove some connectors to get at the card but I'm not 100% how they work so don't want to start pulling. Do I just pull them out or do they some how unhook?Any help would be much appreciated.CheersBen

author: rs20
author_rank: Super Contributor
timestamp: January 13, 2016, 06:46:44 am
content: I'm not an expert, but I think replacing the pots is the best way to go if you can find them.As for the flat flex cable, yes, you just pull them out I believe. For maximum chance of success, make sure you hold on to it close to the plug, so that you get some purchase on the stiffer bit (the "protect board").

author: cmscss
author_rank: Newbie
timestamp: January 13, 2016, 06:59:20 am
content: Thanks heaps for the reply,I've pulled the front aluminium frame off exposing the pots (see attached - RV1300 & RV1210).I'm thinking I could just desolder/resolder without removing the card as there's a confusing amount of plugs and wiring going into the back of the boards.What do people think about doing it that way?CheersBen

author: cmscss
author_rank: Newbie
timestamp: January 13, 2016, 07:16:19 am
content: Actually, I thought the pots were just a double arrangement like the level pot I saw first but the shaft goes through to a square box on the back (see attached).Where would be the best place to search for these types of pots - or do you think I'd be out of luck?Or could I disassemble them and try to straighten the shafts by themselves - or are pots too fiddly?Any help or pointers in the right direction would be much appreciated.CheersBen

author: tautech
author_rank: Super Contributor
timestamp: January 13, 2016, 07:34:35 am
content: Man do I hate to see this.While they might not be unobtainium, they won't be easy to find and attempting to straighten them will probably result in breakage.To dismantle them youmayhave to remove the Ali splined end from the brass shaft or that shaft is possibly inserted into the second pot and held there with a circlip or E clip behind the first pot.Removal from the PCB shouldn't be too hard if you've had some practice at salvaging components.Careful study and some thought should reveal how they've been assembled.Or fingers crossed and use them as they are.

author: cmscss
author_rank: Newbie
timestamp: January 13, 2016, 07:49:12 am
content: Thanks for the reply - yes, very painful especially when it was due to terrible packaging from an Ebay seller.I got a full refund (including shipping costs) so all good but it's a shame as it's in good shape and looks to be great analog scope complete with cursors.Anyway, only one of the pots is really bad (very difficult to turn) so I'll proceed slowly and see what I can figure out.The service manual lists the pots as part number:3142080AVR Carbon, 16 type, 10KB+50KB with SWIf anyone else has some ideas, feel free to chime in.Cheers and thanks heaps for all the replies, much appreciated.Ben

author: tautech
author_rank: Super Contributor
timestamp: January 13, 2016, 07:55:25 am
content: Quote from: cmscss on January 13, 2016, 07:49:12 amYou say it is the H Position pot, that'll be one of the shafts, what's the other?Service manuals usually have a BOM and codes to identify the component manufacturer, tihs may help find a replacement.

author: cmscss
author_rank: Newbie
timestamp: January 13, 2016, 09:50:39 am
content: Thanks for the reply,Yes, the problem shaft is labeled H POSITION and the other is labeled VAR HOLDOFF with a pull labeled SWP VAR - not sure what this one does. But while this second one is also bent, I can turn it and it works fine. The H POSITION shaft is almost impossible to turn.And yes, the service manual shows both to be identical parts: P/N 3142080A - VR Carbon, 16 type, 10KB+50KB with SWBut I haven't had any luck searching or finding based on the part number as yet.CheersBen

author: MrSlack
author_rank: Frequent Contributor
timestamp: January 13, 2016, 10:14:33 am
content: They are standard pin mount P16 pots as sold by Omeg/Alps. Switch is probably a DPDT looking at the pins.The only pain is that it's easy to get dual gang ones without a switch and single gang ones with a switch. Not sure if you can bodge a triple gang and a switched one together to produce some human centipede analog though...Edit: Bourns PDB183 may work but you can't get them in different taper resistances per gang. Again, might have to bodge.

author: cmscss
author_rank: Newbie
timestamp: January 14, 2016, 02:02:55 am
content: Thanks guys,I've unsoldered the unit and bent the pins back to start pulling it apart but it looks like the resister track in the first pot is doubled over and broken which accounts for the noise and grittiness when turned.And the middle shaft is almost impossible to turn independently. I've had a go at bending the shaft but all I've succeeded in doing is marking the shaft as I forgot about a cloth.Overall, it looks pretty poked so it must have had a hard knock - it took a lot of work to bend the front aluminium face of the unit back into shape.What a shame as it looks to be a great unit.Thanks for the links and you're right, a double pot with switch is the option that's missing from Bourns but I'll email them anyway.CheersBen

author: cncjerry
author_rank: Unknown
timestamp: January 14, 2016, 03:38:45 am
content: if you can get the shafts apart, take a picture and maybe I can make new ones for you. You would have to cover the cost of shipping is all.I hate when people do a bad job of packing. One of my favorites was an old HP DMM I bought with the original box, manual, leads, etc. The idiot I bought it from wrapped tape all over the original box and ruined it.

author: AF6LJ
author_rank: Unknown
timestamp: January 14, 2016, 04:31:35 am
content: Carefully take it apart, save the parts you may be able to cobble together a replacement from a combination of new and existing good parts.The hard part will be the center shaft.You need to see if you can straighten it.if you can do that you can most likely be able to pick up what you need to cobble together a new control.Good luck and be careful.

author: cmscss
author_rank: Newbie
timestamp: January 14, 2016, 07:18:08 pm
content: Thanks guys, will have another look at this tomorrow and will be much more patient.

author: Cubdriver
author_rank: Unknown
timestamp: January 14, 2016, 09:14:59 pm
content: I hate morons who can't pack things worth a damn. It seems as though it should be something easy to do, but far too many are incapable of it.Good luck with the repairs - as others have mentioned, hopefully with a combination of various parts you can make up a Frankenpot that will work.-Pat

author: MrSlack
author_rank: Frequent Contributor
timestamp: January 14, 2016, 11:41:06 pm
content: Even the best courier can mangle the best packaging I have found. I sent an HP power supply (computer one, not bench one) with 9 inches of bubble wrap and a box around it and ParcelForce here in the UK managed to puncture it and bend the casing.

author: Joule Thief
author_rank: Regular Contributor
timestamp: January 15, 2016, 12:07:04 am
content: This site may be of some value in searching for ganged potentiometershttp://www.futurlec.com/PotRot.shtmlmy apologies - you need independent duals - not gangedgood site none the less