Hameg HM604-2 disassembly - Page 1
Forum section: electronics / beginners

author: dutch fisher
author_rank: Newbie
timestamp: July 06, 2016, 10:20:15 pm
content: Hello Boys and Girls,I've just bagged my first CRO, Hameg HM604-2, from ebay.Got it today and went thru the accompanying user manual, all seems fine, bar a couple of things.Both channels magx5 pull-push switches no longer push, they only pull, ie pull all the way out, shaft along with knob.I noticed on Dave's HM205 ebay $19 bargain his did the very same.Question is, has anyone disassembled a 604 (or even a 205) to fixed this?How did you go about it?Can it be done without de-soldering?My electronics skill is zero, I bought the CRO to monitor CDI ignitions.CheersDutch

author: MosherIV
author_rank: Super Contributor
timestamp: July 06, 2016, 10:43:25 pm
content: HiQuoteIf by CDI ignitions you mean Capacitor Discharge Ignition - be warned spark plug ignition usually involve 1000s of volts.The most a CRO can handle even with x10 probe is a few hundred volts.You can get x100 probes. Never used them before so do not know if they will work for spark plug ignition.Try this page for a service manual (though it looks to be in German)http://frankshospitalworkshop.com/equipment/workshop_equipment_manuals.html

author: dutch fisher
author_rank: Newbie
timestamp: July 07, 2016, 08:33:07 am
content: Hi MosherIV,Yes CDI ignitions do knock out 30,000v on the HT and 300v on the LT, however i'm monitoring the timing and triggering circuits which are +/- 5v, so all good.I have the english and larger german manuals, however neither have any description on complete disassembly.I could do with any advice from someone who has actually done it.

author: Gyro
author_rank: Super Contributor
timestamp: July 07, 2016, 09:06:15 am
content: Well if you're used to doing stuff with cars then a mechanical issue with a scope shouldn't pose any problems. I'd make sure it's unplugged, pull the lid off and take a look. It sounds as if the shafts have just become detached from the internal switches, you'll probably find that either clamp screws have come loose or some plastic fittings are unclipped or broken (probably nothing that a bit of heatshrink wouldn't fix).The only caution is to make sure you don't touch anything high voltage that is still charged like PSU capacitors or the EHT connection to the side of the tube (respect the same way as plug leads). Basically look what you're doing.It's hopefully a simple fix, you can always remove the cover, take a look and put it back on if you don't like what you see.

author: tautech
author_rank: Super Contributor
timestamp: July 07, 2016, 09:21:20 am
content: Quote from: dutch fisher on July 06, 2016, 10:20:15 pmYeah right, sounds like you have a good idea what you're doing.As Gyro says it should be pretty straight forward mechanically.

author: dutch fisher
author_rank: Newbie
timestamp: July 07, 2016, 10:26:18 am
content: Quote from: tautech on July 07, 2016, 09:21:20 amErr no, putting the shaft back on the connector, yes, getting access to the connector, no.If you look at eevblog #502 on YT @31:10, you'll see the metal shielding that surrounds the CHI&II mini boards.The 604-2 shielding is even greater than the 205. When I find my camera I'll do a photo.I could access the CHII connector by grinding a small slot in the shield to access the grub screw on the connector.Access to the CHI connector is impossible without disassembly.Regardless, I think the connectors have failed not due to the grub screws coming loose, but because the connectors have split (plastic poss. nylon). I'm fairly sure this is the case as it has happened to the Delay fine adjustment connector (exact same design/material and easily accessed).A glued repair will do the trick.So yep, using my engineer eye, its a almost complete teardown to access, unless someone has a tip/trick.Cheers again

author: Gyro
author_rank: Super Contributor
timestamp: July 07, 2016, 10:51:35 am
content: Ah, that's a shame. As they are just the Y-channel x5 buttons it's debatable whether they're worth that amount of effort, you're unlikely to need them for your application. Maybe just secure them safely from the front.Edit: Hopefully you can get enough access to just ensure that both switches are in the 'out' position.

author: dutch fisher
author_rank: Newbie
timestamp: July 07, 2016, 10:54:14 am
content: That's very true, but getting everything working on my gear is an itch I have to scratch.

author: MosherIV
author_rank: Super Contributor
timestamp: July 07, 2016, 10:55:53 am
content: QuoteSorry, never worked on Hameg analogue scopes before. Worked on my Tektronics before.QuoteIt should be possible to access everything in scopes of this era. They were designed to be very serviceable. It is usual to have to dismantle quite a bit of it just to get to some parts.

author: oldway
author_rank: Super Contributor
timestamp: July 07, 2016, 05:29:21 pm
content: I had a look on my HM 605 and it seems not to be that difficult.I think you must remove the front panel.Than, it is easy to remove the two attenuator/preamplifier circuits.You will have to dessolder the shields to gain access to the broken plastic couplers.