Hameg HM605 issue. - Page 1
Forum section: electronics / beginners

author: davelectronic
author_rank: Frequent Contributor
timestamp: July 22, 2023, 12:44:28 pm
content: I have an old Hameg HM 605 60Mhz ocillascope, I was hoping to measure some DC power supply noise or ripple of these power supplys. I've had this scope for a long time, but hadn't got round to using it yet. I have noticed when I centre the trace, it looks short on the graticule scale by about 2mm and each end of the trace. When I use the probe to look at the built in wave form, it looks like it does go completely to each end of the graticule scale. I'm an absolute newbie to using ocillascopes. I only know what I've gleened from you tube and books. So my question is, does this trace look short on each end once I've centered it ? It only looks like this when the refresh rate is fast, if I slow it down, the trace looks like it starts and ends accurately from end to end. Any help appreciated, and thanks for reading.

author: RAPo
author_rank: Super Contributor
timestamp: July 22, 2023, 12:58:54 pm
content: The trace on my Hameg 605 covers the whole graticule (and even a bit more) at the fastest time settings.Look for bad solder joints in the area of the X-POS, the HOLD OFF and the TIME/DIV. pots

author: RAPo
author_rank: Super Contributor
timestamp: July 22, 2023, 01:09:02 pm
content: One more option: is the component tester-knob pushed in? That will shorten the trace.

author: davelectronic
author_rank: Frequent Contributor
timestamp: July 22, 2023, 04:04:17 pm
content: Ok, thank you for your replies, yes the component button does shorten the trace. But when realesed it goes back to the normal, be it short by about 2mm trace. Guess I better look for some dry solder joints then. I'm a newbie when it comes to the outside, let alone the inside. I'm familiar with the HT circuit inside there, so will take care making sure everything is discharged.

author: davelectronic
author_rank: Frequent Contributor
timestamp: July 22, 2023, 05:09:32 pm
content: I've had a look, it's to complex for me to do, I didn't see any obvious dry joints. But found what I believe to be a bodge on the time switch.

author: RAPo
author_rank: Super Contributor
timestamp: July 22, 2023, 05:21:05 pm
content: Is repair really needed? Can you measure signals reliably?

author: RAPo
author_rank: Super Contributor
timestamp: July 22, 2023, 05:29:54 pm
content: Loook in the service manual under the caption "Timebase".Trace length should be 10cm and can be adjusted by the pot for sweep amplitude.

author: davelectronic
author_rank: Frequent Contributor
timestamp: July 22, 2023, 08:13:39 pm
content: I don't know if repair is necessary, but there is still four green wires that don't look like they belong there. The soldering on them is not factory standard, someone has added those wires to the time base rotary switch. I've no idea what there there for.

author: tunk
author_rank: Super Contributor
timestamp: July 22, 2023, 08:34:41 pm
content: How does the test/cal-signals look like?If they have the correct voltage, then you shoud be able to measure noise/ripple.If you want the peak values, you could set the time base to the slowest.

author: davelectronic
author_rank: Frequent Contributor
timestamp: July 23, 2023, 11:31:47 am
content: Yes I have connected a probe and looked at the built in test signal, that works. I just don't know how accurate it is overall. And I haven't tried every function, I just don't have much confidence in a scope that's been messed about with. As for the green bodge wires, they bridge multiple large pins that are bridge inline. I haven't checked yet, but I'd guess it's a grounding of some sort, just because it's connected to several already connected pins. But no idea why it's been done.

author: RAPo
author_rank: Super Contributor
timestamp: July 23, 2023, 11:46:44 am
content: If you can't fully trust your scope, it is worthless for practical work.Consider it done and maybe you can still repair it a bit.Hope you didn't spend too much money on it.

author: gjvdheiden
author_rank: Contributor
timestamp: July 23, 2023, 12:24:38 pm
content: At 15:21. Those wires are even in the manual. Nothing wrong with them.

author: RAPo
author_rank: Super Contributor
timestamp: July 23, 2023, 02:03:50 pm
content: Yes that was a horror video :-).I've just bought a Hameg 208, and I am thinking of retiring my Hameg 605 now.