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Old 7th Jul 2020, 12:44 am   #41
Chris55000
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Morning Dave!

Yes, the OAZ271 zener diode would clamp the square–wave to approximately 7.5V to 8V peak–to–peak, and this would occur whether you have the early version shown in my layout–drawing fed from 155V or the later version shown in the books fed from 46V.

Incidentally Solartron did a hopeless job on their CD1400 Main Frame Component Layout Diagrams, none of the artwork matches the component overlay!

Circuit diagrams to match my replacement Component Layout Diagrams will be provided and a full wiring diagram of the three CD1400 Main Frame Boards will follow on at the end!

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Old 7th Jul 2020, 6:02 pm   #42
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Removed as much solder a I could from the two tag 14 artworks and am sure as I can be that it is a common artwork that both tag 14's connect to.
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Old 7th Jul 2020, 8:33 pm   #43
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Hi!

I'll amend my sheet to show that and re–upload it! Work on the other two board layouts and circuits is ongoing and will be uploaded when completed!

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Old 8th Jul 2020, 12:08 am   #44
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Repaired numerous bad soldered joints on Board 1 and refitted/reconnected wiring connections. Refitted Board 3 & connected some of the wiring. Deduced that the yellow wire that solders to a pin on Board 3 that I previously worked out was the missing tag 6 connection is in fact tag 9 wire for the Cathode Lower (KL) so it is tag 9 that is not fitted on this old board.

Repaired dodgy soldering at C4 on rear of CRT for the Z modulation.

Tested the Brilliance, Focus, Astig, Set BA and the Set I.P.S. potentiometers voltage range of operation, all good.
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Old 11th Jul 2020, 2:56 pm   #45
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Hi!

Please note that the provisional layout diagrams I will provide aren't super–accurate enough to make replacement PCBs from, they're only a guide after all, but if anybody needs any making because an original is badly damaged by overheating, or has burnt–up too much to repair, please PM me with the exact physical dimensions of the board needed and I'll get onto it!

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Old 14th Jul 2020, 5:07 pm   #46
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

For the record, the voltage measurement results from Post 44 were:-

1. Brilliance Upper - min -ve 818 volts, max -ve 736 volts, Brilliance Lower - min -ve 822 volts, max -ve 733 volts.

2. Focus Upper - min -ve 394 volts, max -ve 680 volts, Focus Lower - min -ve 385 volts, max -ve 670 volts.

3. Astig Upper - min +221 volts, max +308 volts, Astig Lower - min +210 volts, max +307 volts.

4. Set BA - min +122 volts, max +212 volts.

5. Set I.P.S. min +222 volts, max +310 volts.

6. Cathode Lower (KL) -ve 751 volts, Cathode Upper (KU) -ve 767 volts.

7. Board 3 tag 13 -ve 140 volts.

8. C.R.T. Balance wiper (2 fixed resistors) -ve 845 volts.
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Old 15th Jul 2020, 11:05 am   #47
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Hi!

All those voltages are nicely balanced and about the right range to be expected now!

The main difference between your version of the CD1400 power supply and the later production versions relates to the heater supplies - on your version the heater circuit from T1 winding 23-24 is earthed by the PCB earth-return leads, on later production it was returned to tag 11 at the mid-voltage point of the h.t. doubler rectifier to elevate it to +180V approx., in order to prevent the heather-cathode ratings of the final amplifier valve stages being exceeded.

My diagram will make this clear!

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Old 15th Jul 2020, 10:40 pm   #48
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Reconnected the remaining connections to Board 3 including the EHT connection cable, found EHT cable soldered connection was broke at the CRT end (PDA connector) so repaired it.

Checked the EHT voltage as far as I could, do not have anything to measure the full +3.2kV, can only go up to 2.5kV with the Avo

Measured the EHT at the first half of the HV voltage doubler at junction of HV diodes MR304 & MR305 at around 1,750 volts, assume the full output at junction of MR305 & C312 would be around double this value.

Measured the full EHT output at 2.5kV by adjusting mains variac for 190 volts.

Next will refit the X & Y timebase plug in modules and hopefully will have at least one good trace.
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Old 16th Jul 2020, 12:37 pm   #49
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Refitted the timebase modules.

Get a reasonable (fully adjustable) Upper trace but as at the beginning still no sign of the Lower trace. Will have to scope check the X timebase drive signals to the CRT X plates.

Various problems with the Y timebase operation including:-

1. No trace if X10 input gain selected.
2. If AC coupling selected the trace drifts upwards and after 30 seconds disappears (OK on DC coupling).
3. V/cm input switch calibration out and some positions do not work at all.
4. Basically responds to the 5V scope test point signal OK but does not respond correctly to the larger amplitude Timebase out test point.
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Old 19th Jul 2020, 10:21 pm   #50
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

X plate drive signals look good as well as all the other CRT connections, so still to work out why no second trace ?

One possible strange thing is that with either X1 or X2 drive signal disconnected then only then get a partial width trace
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Old 19th Jul 2020, 11:39 pm   #51
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Hi!

You will only get a pertial-width trace if you disconnect either X1 or X2 because of the way the CRT is built, the various alignment and screen electrodes interact with each other, and you only get a partial scan with one plate driven.

The next step is to switch off the 'scope, allow all the capacitors time to discharge, then transpose all the "U" gun and "Y-plate Upper" leads on the CRT with those for the "L" gun and "Y Plate Lower" and test the oscilloscope again - if you still only get an upper trace, the lower gun of the CRT is duffy, most likely an internal cathode or first anode disconnection.

If the Upper trace now disappears but the Lower trace appears, there is still some fault associated with the electrode potentials concerned with the lower gun controls and the "Y1U" and "Y2U" deflector plates, so you'll have to go thro' them all meticulously!

Have you made sure both gun heaters are correctly alight? - there are only two heater pins so if one of them is out it's another CRT time!

If you do find the CRT at fault I doubt you'd find another blue one (P11 phosphor), so you'd need to get the perspex and coloured filter-piece with the replacement CRT as well, green most likely!

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Old 20th Jul 2020, 8:33 am   #52
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

PS!

Third paragraph in my last post should have been:–

"If the Upper trace now disappears but the Lower trace appears, there is still some fault associated with the electrode potentials concerned with the lower gun controls and the "Y1L" and "Y2L" deflector plates, so you'll have to go thro' them all meticulously!"

I'll discuss the wandering trace you get when you select "AC" coupling on one of your plug–ins in a later post but let's worry about getting both traces up and straight and even first!

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Old 20th Jul 2020, 9:03 am   #53
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Thank you Chris for the useful information and suggestions.

Yes am concentrating on hopefully getting 2 traces working before starting to look at apparent Y timebase issues.

I think both gun heaters are alight OK, top and bottom there are extra bright areas, a little difficult to be sure as the whole circumference of the tube neck lights up.

Was considering swapping over the wiring, to see if fault switches over to the Upper trace, will try that a little later.

A few days back I removed the CRT escutcheon to clean dust off the graticule and saw that the CRT trace phosphor look blue and there is also a blue Perspex filter.

David
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Old 20th Jul 2020, 7:30 pm   #54
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Hi!

The normal accumulation of dust and grot, etc., on the base of the CRT neck will tend to diffuse the light from the heater/cathode assembly somewhat making the whole interior appear to glow, but if the glow you can see is a very bright pale orange/yellow there is a possibility that one of them for the lower gun assembly could well have gone out or high–resistance, or even be partially short–circuited.

The quickest check is to see if the cathode voltage regulator neons V301 and V302 are both correctly alight, as the current flow via the focus control/intensity control chain from chassis–earth down to the cathode pins of the CRT is insufficient to allow them to strike on their own, the neons also rely on the CRT gun's cathode–current in part flowing into them for correct stabilisation.

If you have any doubts about these neons, they are available cheaply n.o.s:–

https://www.ebay.co.uk/itm/392821963663

Anyway, go through the intensity/focus chain again, making sure both kL and kU are correctly returned to the –e.h.t. Supply via the external Board 3 wiring.

Don't forget that valve and C.R.T. electrodes are "dead–end" open–circuits when the devices are cold, so what you resistances you read on a d.m.m. is what there actually is – there's not usually any semiconductor "shunting" effects in all–valve circuits to worry about – the diagrams will give you a guide as to what you should read!

Chris Williams
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Old 21st Jul 2020, 8:45 pm   #55
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

With Board 3 fitted, it is impossible to see V301 & V302.

After removing control knobs and board securing screws partially hinged out the board and provided paper insulation to stop the various wiring connection tags from shorting down.

The 2 neon valves are lighting up but one of them is secured with a P clip so difficult to compare brightness levels, I will remove the P clip and compare better.

However now (since moving the board) I have lost the previous visible Upper trace, so need first to find out what has happened.
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Old 21st Jul 2020, 10:06 pm   #56
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Hi!

The original Hivac "Signalite" datasheet suggests these neons don't give a lot of visible light because their envelopes are quite heavily "sputtered" internally in manufacture, but the normal voltage across them in operation is normally 84 ±2V, and they're designed for stabilization over an operating current range of 0.1 to 2mA.

Almost certainly you're probably disconnected the upper gun's cathode lead, or one of the other common electrode leads when disturbing the board, so recheck the kL and kU leads, and also the A1 and the blanking–off anode lead AM – the A1 of the CRT obtains +160V from the X/TB unit SKTC pin 8 – this supply is derived from the h.t. cathode–follower dropper valve V7a pin 3 – the one mounted horizontally on the small bracket.

The Blanking–Off anode AM has a sweep–length positive–going "unblanking" pulse varying between +160V (quiescent) and +220V (sweep active), from the anode of the unblanking/gate pulse amplifier V4A (ECF82 pentode), thence from pin 16 on the T.B. PCB and SKTC pin 9 to the AM Blanking–Off anode (pin 11) of the CRT base end pins – check all these connections!

Disconnection of either the A1 or AM leads will blank off both traces as these two electrodes have a common connection to both upper and lower CRT gun's.

Chris Williams
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Old 22nd Jul 2020, 9:02 am   #57
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Thank you Chris, all the connections at Board 3 and the main voltages check out OK.

Still to check A1 & AM, will first refit Board 3 as it is a bit precarious partially hanging out.

David
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Old 22nd Jul 2020, 11:43 am   #58
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Before refitting Board 3, I rechecked all the voltages and found that tag 3 (A3U) was very intermittent, a lot of the time no voltage and occasionally for short period good voltage. This is the Upper wiper connection for the Astigmatism (Astig) pot to the A3 electrode.

Found the other end of the grey wire was just about hanging off the end of the A3U pin on the CRT, this wire is extremely tight if Board 3 is moved away from its fitted position.

Correctly fitting the wire to A3U has returned the Upper trace to operational.

Removed P clip and both neon regulator valves look similar brightness, no obvious difference if A3U is connected or not connected.
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Old 24th Jul 2020, 9:45 am   #59
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Hi!

I wonder if you need to renew all the wiring between the CRT base, Board 3 and the wiring between Y1L, Y2L and SKTA/SKTB?

I fully appreciate that trying to renew individual wires in laced wiring–looms etc., is a "pita", but renewing all the wiring at one go is usually a bit easier if you can get at both ends of it all!

I think that 0.11" or 0.187" non–insulated spade connector tags should be suitable for the push–on connectors on board 3.

It's possibly beginning to look like you've got internally intermittent wiring between the CRT electrode connections and the rest of the oscilloscope and a rewire might be in order, but before undertaking this project you need to ascertain by swapping over the lower gun and lower Y plate wiring, as per my previous suggestion, that the lower gun of the CRT is capable of producing a trace!

If the CRT turns out duffy, then replacing it with another, including the appropriate perspex filter, the associated wiring and Board 3 complete (if you get another main–frame rather than just a CRT on it's own) is the most likely way of getting a working CD1400 main unit to repair the plug-in units with, they're not exactly rare – I get notified of new listings every day practically, but so far only seen one unit with an orange CRT and no blue ones yet!

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Old 24th Jul 2020, 4:47 pm   #60
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Default Re: Solartron CD 1400 Oscilloscope Refurbishment

Hi Chris,

Good suggestion, it is just a question of finding/making time to do it amongst many other ongoing jobs. Definitely will swap over the lower & upper wiring.

David
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