Gould 3100 oscilloscope (Hitachi V-1100A) - Page 1
Forum section: electronics / testgear

author: shakalnokturn
author_rank: Super Contributor
timestamp: September 18, 2019, 08:53:17 pm
content: I have one of these with some problems to solve so I'm looking for a service manual or service manual for anything similar in it's family.A user manual could also be handy.Anyone out here know how you change the probe ratio? This thing has no probe sense rings and I'm stuck on "P10x".I can't seem to make any sense of the blue text on the keypad either, what's that about?Edit: Changed title including Hitachi model.

author: The Senate
author_rank: Newbie
timestamp: September 19, 2019, 02:01:39 am
content: This thread may be of help. It refers to the 3150, but it looks very similar to yours.https://www.eevblog.com/forum/testgear/gould-3150-analog-oscilloscope-need-user-manual/

author: shakalnokturn
author_rank: Super Contributor
timestamp: September 19, 2019, 06:13:43 am
content: Thanks for the link!A quick guess after reading that revealed it's a rebrand of the Hitachi V-1100A.The user and service manuals are available.

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 02, 2019, 11:03:15 pm
content: Opened the case, sprayed a few connectors tightened a few screws and the display was back on centre. Funny as when it was off to the top a good tapping had no effect.I replaced the backup capacitor for the front panel settings.Also dumped the EPROMS, there are dumps of a v4.0 on ko4bb but it's uncertain whether those are for the "A" or non-A version of the scope, so I'm joining my v3.3 files.Now I'd like some clues on a CRT ghosting problem. I've had plenty of experience with TV CRT's but very little with CRO's.I can get acceptable focus but still not as crisp as I like it and have tried readjusting the astigmatism.The beam has a ghost to it, making the viewing uncomfortable with a lot of background illumination, this happens even without turning the brightness very high.Ghost intensity varies with trace intensity, it's focus also follows the trace focus, it's position though is offset depending on trace position.If the spot is centred the ghost is also but as the spot moves off-centre the ghost moves off in the same direction before the spot. Attached photos showing spot in two positions and traces using beam finder.I have not touched the "CRT Bias" trimpot not being sure of it's use.

author: tautech
author_rank: Super Contributor
timestamp: October 03, 2019, 05:32:10 am
content: That trace ghosting isn’t apparent in pics in the OP.Has it only appeared after your work on the scope ?Have you checked the EHT voltage is within spec ?

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 03, 2019, 09:39:42 am
content: Quote from: tautech on October 03, 2019, 05:32:10 amHard to say, it didn't look fantastic in that respect to start-off with in original pictures, but at that point I was focusing on the offset problem, so may not have paid attention to the ghosting. Also on the second set of pictures adjustments and lighting conditions were set to emphasise the case. I don't see what I could have done that would have caused such an issue anyway so let's suppose it was like that before...I've since played with the "CRT Bias" adjustment: No effect other than altering brightness.I haven't got round to measuring the 18kV supply yet , all my H.V. probes have drifted, I'm waiting for another one arriving soon from the UK.Looking closer at the screen it appears to have a mesh to it like on storage CRO's, the normal display clearly shows the chess pattern, this also explains why the focus isn't quite as crisp as I expected.The ghost image does not have the chess pattern but rather a more conventional uniform phosphor glow so it looks as if the ghost is caused by part of the beam being scattered by the mesh, depending on the spot position the angle the mesh is hit at could explain the ghost having more offset.(Attached macros with spot voluntarily out of focus.)Now, why this scope would have a meshed CRT... Is it normal or has the CRT been swapped for a storage model at one point? I don't know enough to say.Maybe someone with a similar model can confirm they have a meshy CRT? Does it also ghost to some extent?

author: tautech
author_rank: Super Contributor
timestamp: October 03, 2019, 09:56:22 am
content: Nope, EHT is the -1900V.PDA is the +18KV and you never need/want to measure that !If the minus 1900V is too high it might be the cause of the blooming.It's not clear if CRT Bias is the only adjustment that might affect it or if there is another pot off that schematic.Regardless, there's a few high value resistors connected to the EHT that if drifted high could let the negative EHT voltage become higher than it should be.R1491, R1470, R1475, R1476 etc.Check them all.

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 16, 2019, 01:00:53 am
content: Quote from: tautech on October 03, 2019, 09:56:22 amSometimes you need to do crazy stuff, I did measure the PDA. It's only at about 17.45kV but I'll call that good enough.EHT is at 1.94kV should be good too?I'll check the resistors later.Some recent re-reading of topics on the Tektronix groups.io revealed that this effect is not that uncommon in scopes with high PDA, and though annoying, it may be inherent to the CRT type.Below an extract of the book "Electrical Instruments" by Anton E. Pannenborg also mentioning some adverse effects of high PDA.

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 16, 2019, 09:59:22 am
content: Just been trough the higher value resistors on the CRT biasing, nothing wrong there, even the carbon powder style R1476 was spot on 10M, I had expected that one to drift high.The CRT has another slight defect:First placing a trace spot-on centre and adjusting trace rotation so it matches the X graticule perfectly, then moving two traces to top and bottom limits of the graticule, the traces are not perfectly parallel. Converging to the left, diverging to the right. There is about 0.2div error end to end on each trace.Anyway, without input from someone who has run into this before and can say that it's abnormal I'm going to have to call this a working scope.

author: gweilo8888
author_rank: Newbie
timestamp: October 05, 2021, 10:05:59 pm
content: Quote from: shakalnokturn on October 03, 2019, 09:39:42 amJust stumbled on this thread. As it happens, I have the original Hitachi version of the same scope, and although I'd never noticed it before now I can confirm that mine does indeed show the same mesh, and even with the same slight tilt to the left as shown in your pictures. Here's a rough-and-ready, not-quite-focused macro of my own.I don't see the ghosting that you do, however.