Test Equipment Anonymous

This came from a silent key stall at a swap meet. It was sold as spares or repairs. It's an older and bulkier Hitachi scope. An advantage is it uses bigger components such as resistors and presets than later Hitachis with fiddly 1/8th Watt resistors. It's a 100MHz scope with delay sweep.

I powered it up, but it didn't produce a trace. I tried it again, and it did produce a trace. Sometimes it produced a trace when it was powered up, sometimes
it didn't. If left on, it eventually produced a trace.

I checked the supply rails. They were about right, with no significant ripple, apart from the 5V rail which was at 1.8V. I changed the reservoir cap in the 5V
supply with no change. I thought one of the soldered joints on the 7805 regulator looked odd, so I remade those with no change. I changed the regulator although I've never known one to fail. No change.

Eventually I looked at the soldered joints on the pin header bringing in power from the transformer and sure enough three had circular cracks around the pins. That explained it. They probably only conducted properly when they were warm and expansion made them contact fully. I desoldered and resoldered all of the joints on the pin header and no more 5V problem.

I felt silly for not spotting that quicker. I had the same problem with a 40MHz Hitachi but I found it a lot quicker.


The scope more or less worked with the usual problems caused by controls made stiff by hardened grease, which were freed with lighter fuel and relubricated with PTFE dry lubricant. All the knobs were grubby so I removed them and cleaned them. That made it easier to clean the front plate properly. The delay sweep vernier knob has a 1/32nd" grub screw which I had to order an Allen key for. I cleaned the contacts I could reach easily and thought that the others such as for the 20MHz cut off filter didn't do anything critical and could be glossed over.

I tried the scope out and found that channel 2 almost met the 3dB spec at 100MHz but channel 1 fell far short.

I have a Siglent function generator which will sweep on both channels up to 120MHz and provides a sync pulse. It seems fairly flat over that range. I swept both channels and channel 1 did fall off very quickly. With the 20MHz filter in the fall off was very quick as expected. With the filter out the reponse varied depending on how the button was pushed. The Y preamp board had to come out so the contacts could be cleaned properly. The 20MHz filter switch is connected to the button by a flexible cable rather like a bike brake cable. I squirted contact cleaner into the switches and worked them back and forth. The Volts/Div switches could be accessed easily now and were cleaned again. I washed off the residue with IPA. The board was replaced.

No problems with the 20MHz filter or the other controls, but there was still the poor frequency response from channel 1, this time not altering when the 20MHz filter button was fiddled with.

This is a picture of a 1 to 100MHz sweep of both channels. Channel 1 is the profile that dies off fastest.
I fed both channels a 100MHz signal and traced it through the Y amplifiers with another scope (a 100MHz Siglent with the 150MHz improvement). Everything was comparable until after the second attenuator when the signal changed to differential.

I checked resistors as best I could and compared between the two channels. No particular differences. I also checked voltages, again, nothing obviously different.

There are a few factory selected components. I believe many Hitachi scopes have essentially the same Y amps, with different filtering components to give 40MHz models, 50MHz models etc.

On the schematic, the starred parts are factory selected. There are several.
It occurred that C64 may have had something to do with it and may have failed. I held in place a 120pF cap across it and the frequency response changed greatly. I experimented with a few values and found that a 33pF made the response look more acceptable. I looked and saw that C64 had not been fitted. I tack soldered a small preset cap in the C64 position solder side and adjusted it for what looked like the best response, easily meeting the 3db down frequency and giving a fairly flat response. It was desoldered and measured with an Atlas component tester. 37pF. I tried two 18pF caps and a 20pF and an 18pF. The 20pF and 18pF seemed the best.

Hmmm. Had this just been omitted in manufacture and channel 1 had never met its spec? Had it been found unnecessary but since then other components have drifted?

And so the same treatment for channel 2, which wasn't quite up to spec. C164 was removed and measured at 3.6pF. The preset value that made the two traces nearly the same was 29pF. An 18pF and a 10pF made it nearly right. A 1.2pF made no difference. Adding a 2pF got it right.

At this stage the two channels had near identical frequency responses and the 3dB point was well over 100MHz. The traces deviate towards 100MHz with channel 1 having noticeable greater amplitude, but both comfortably over the -3dB spec.There's a big difference between 0pF (parasitic) and 3.6pF and 30 to 40pF. Had I missed something? I often wonder how these things performed when they were new.
So far so good, but I don't feel I properly understand what those factory selected parts were selected for. They may have been aiming to meet the 3dB point and have a completely flat response. This isn't quite flat. I recall the Tektronix rule is that scopes can be expected to be rock solid and need no allowances made up tp 20% of their claimed bandwidth, which this does. I haven't experimented with the other factory selected parts. There's something unsatisfying about this suck it and see bodging.

I went through the set up procedure a couple of times. The scope works well enough on all functions.

There's a slight overshoot on a 1MHz square wave on channel 1 which I can't adjust out. The manual says to adjust for a 0.1 div overshoot on a 1MHz square wave 5 divisions high, which I suppose this is, but I don't like to see it.

Here it is displaying 1MHz triangle and square waves in a classic ebay working pose. I should have put the camera on a tripod and arranged better lighting and a neutral or more congenial backdrop for an ebay photo. If you look carefully at those ebay photos, they are usually displaying 1kHz signals and the timebase continuous adjustment has been selected for best effect.

Pretty much it works with no glaring faults, all functions work and I've had enough of messing with it for now. I don't feel I've got it quite right. I may revisit it later. The scale illumination doesn't work and uses wire ended bulbs which are now quite expensive. Only one of the original bulbs is there and it's dead. I may look into replacing them with LEDs.

It's a working 100MHz scope with delay sweep. The display isn't as sharp as later Hitachis but sharper than a Tek 475. It would be usable as an every day scope. It doesn't use a load of ASICs and hybrids. The delay sweep timebase knob is quite chunky, not like the very nice, but delicate one on Tek 400 series, which is often broken or cracked. On many scopes the trigger view done with a momentary contact switch. With this you can turn it on permanently. They mention channel 1 and channel 2 - fair enough. They also have labeled channel 3 and channel 4, which are the external trigger and the delay trigger, which you can view with the trigger view. I suppose others do that too, but it seems like marketing having too much say.

It's a bit big and heavy. Here it's pictured with a Tek 465. It gives the impression of being much bigger and heavier.

Those Hitachi scopes are nice machines, sometimes I regret flipping mine but something had to give, I was running out of space rapidly, much the same as I am again, this time with calculators taking a lot of space.

I now have four; two V422s (40MHz), a V525 (50MHz) and the V1050F (100MHz).

As sub top tier (Tek, HP, Lecroy) scopes that I've had my hands on go, I think they are impressive. There are a lot I haven't tried, such as Philips and Iwatsu.

They are relatively easy to dismantle and work on. Typically you don't have to desolder things to remove a board. They don't use too many unobtainium parts. They use Japanese transistors, but mostly you can get them, they have Western equivalents and transistors rarely die anyway. The manuals are fairly good, and while not up to Tek or HP standards, they are certainly usable and much better than some. When they have been sorted out they are nice to use and with very good, sharp displays.

I suppose I should think about selling some of them on. Of those four, the V525 would be the hardest to part with.

You're far better harbouring calculators than oscilloscopes.

Zenith wrote: ↑Thu Oct 05, 2023 11:36 am ...You're far better harbouring calculators than oscilloscopes.

Sage advice, that.

mnem
like smoking, the best cure is don't start.

Zenith wrote: ↑Thu Oct 05, 2023 11:36 am I now have four; two V422s (40MHz), a V525 (50MHz) and the V1050F (100MHz).

As sub top tier (Tek, HP, Lecroy) scopes that I've had my hands on go, I think they are impressive. There are a lot I haven't tried, such as Philips and Iwatsu.

They are relatively easy to dismantle and work on. Typically you don't have to desolder things to remove a board. They don't use too many unobtainium parts. They use Japanese transistors, but mostly you can get them, they have Western equivalents and transistors rarely die anyway. The manuals are fairly good, and while not up to Tek or HP standards, they are certainly usable and much better than some. When they have been sorted out they are nice to use and with very good, sharp displays.

I suppose I should think about selling some of them on. Of those four, the V525 would be the hardest to part with.

You're far better harbouring calculators than oscilloscopes.

If you ever get your hands on a Iwatsu SS5710 I can really recommend you do, it is only a 60MHZ machine, but it is beautifully made and has 4 traces, albeit 2 are only for low voltage inputs.

Anyway, I have the following manuals in my collection that might help you if you pick any up.
Iwatsu SS7610, SS7611, SS7607, SS7606, SS5710, SS5710E and SS5711

Phillips PM3110 and PM3217

Thank you. I shall mark that down for reference.

The only Iwatsus I've seen recently are 20MHz ones which looked decidedly tatty, so I wasn't interested.

Around 15 years back I was offered a 100MHz Iwatsu when I visited a well known electronics/junk shop which was closing down. A 100MHz scope back then was not cheap. Even though it was a closing down sale, he still wanted top wack. He asked fifty notes for it. It didn't work but he said it only needed a bridge rectifier. A likely story. As if a character like that wouldn't bung in a 50p rectifier, show it working, and ask at least £100 for it. I looked on the WWW and Iwatsu manuals were virtually non-existent. All considered it was not one to chase.