Solartron CD 1400 Oscilloscope Refurbishment

[DMcMahon]

Yesterday I started checking out my recent acquisition (FOC from Atlantic 52 through "Sets, Parts and Service Information Offered") of late 60's double beam oscilloscope Solartron CD 1400, including several spare timebase plug in modules.

Its last known operational status was" There is a beam albeit a bit dim & defocussed and scans to the left of the screen".

Because it has been powered up fairly recently I dispensed with the usual safety checks and powered it up (after checking for correct fitted fuse values).

No trace/display could be obtained at all with any timebase settings, graticule lighting illuminated and after a few minutes I could smell the valves warming up.

Removed the outer cover to investigate, everything inside was heavily coated with dust and lots of fluff present. so spent quite some time removing the worst of it, will continue more cleaning as time goes on.

After cleaning the dust off three wire wound resistors on Board 1, saw that one of them looked somewhat overheated and had lost some of its enamel coating.

These resistors are R105/R106/R107 all 680 ohm 4 watts and feed the decoupled +320 volt HT supplies to the 3 timebase modules, R107 being the suspect looking one which feeds the X timebase module.

I tried to measure the 3 resistors but could not get any sensible readings (I think due to old oxidised solder joints being high resistance on the surface), so unsoldered them and remeasured, they measured OK (R106 was a little high). Refitted the resistors, but still no display, measured the voltages at the resistors and one (R107) was bad (no volts), found that the 2 tracks that the resistor was soldered to had broken away (looks like the tracks are quite fragile when disturbed).

Repaired the connections and got good voltages (around +350 volts at output of the resistors). Now have a display/trace from the upper Y module. Have some control over it, can make it into a free running spot by changing the time base speed, but Focus does not work, nor Y shift and brilliance does not work properly.

All valve and CRT heaters appear to be powering up.

So a step in the right direction but plenty to do still I think. Next I will swap over the 2 fitted Y timebase modules to see what happens. Then will go back to basics and check out properly all the numerous power supply voltages before looking at the timebase modules in more detail.

David

[Ed_Dinning]

Hi David, if you have a circuit, or can trace the "tube network " ( a string of resistors and pots across most of the tube electrodes) you may find that some of them have gone high in value or leaky caps.
This will upset the voltages on the tube electrodes an give problems as you describe

Ed

[DMcMahon]

Hello Ed,

Yes I have the original manual that came with it, so will be checking all the various circuits, just need to find/make time to do it. The spine of the cover for the manual is broken, so all the pages are loose but other than that, it is in good condition, very detailed to.

I also downloaded the same manual, but the downloaded version additionally shows the expected waveforms on the various circuits.

David

[DMcMahon]

Swapped over the two Y timebase modules, still get the trace only on the Upper position.

Scope probed the Calibration test points, the Timebase out test point and the Test probe test point, all reasonable good apart from nothing on the 5mV calibration test point.

Connected the test points to the Y input but no sign of any signals, same with either Y timebase module fitted in the upper position.

Partially removed Board 3 (one I had not looked at previously, very dusty, found 5 of its push on cables connections pulled off, possibly could have come off while accessing the board, will refit once have worked out where they connect to.

[DMcMahon]

Tried to clean up Board 3 in-situ but too difficult, so removed it completely. The manual says the wires and the terminal posts on the board are identified but they are not on this one.

Cleaned the board up, really messy and sticky. First thing noticed that the board part number of 14009003 is different from the manual documentation which lists it as 14009103.

Also could see that the board has had some attention before with soldering being disturbed. One of the two K8/50 HV Selenium rectifier diodes has been replaced by an ITT TV20-16K80V dated 1972. Could not get any resistance or diode readings using normal methods for both of the HV rectifier diodes.

Resistor R302 (10k) is a fairly modern looking resistor so has been replaced at some stage. It is on the output of the -780 volt voltage Tripler for use on the CRT electrodes.

Basically the board is the same as the documentation but there are technical differences. The schematic and parts list show a CRT Sense Balance potentiometer RV 304 but it is not shown in the Board Component Location drawing. This pot is not fitted but there are two 24k fixed resistors in its place. These resistors look fairly modern. Also resistors R309 & R315 are shown as 390k on the schematic and 330k on the parts list but 150k resistors are fitted.

The replacement HV rectifier diode TV20-16K80V has one broken leg, looks like it may be repairable by soldering.

The three EHT capacitors C306/C312/C313 (0.07uF, 2kV) are in a right mess with very sticky wax. One (C306) is totally shot and does not measure any capacitance just measures 200 ohms.

C312 measures 114nF and 0.8 ohm ESR and 50Mohm insulation resistance at 1,000V
C313 measures 210nF and 2.1 ohm ESR and 4Mohm insulation resistance at 1,000V

So at least C306 needs replacing and probably C313. Would like to replace them all, may not be easy to find suitable replacements.

Resistors R307 & R314 (47k) are open circuit, these feed the Focus pots so would explain why Focus is not working.

Resistor R312 (27K, 2 watt) is open circuit, this connects the Set BA (Beam alignment), the Set I.P.S. (Inter Plate Shield) & the Astig potentiometers to ground.

Resistor R304 is also open circuit, this one is a bit of a mystery. It is not shown on the schematic and on the part list is listed as "Not fitted" with * note that "Fitted on early models only". Unlike some of the other "Not fitted" components references this one does not state what the value was on early units. It is completely burnt out with no sign of colour codes. One side connects to terminal post # 15, which on the drawing is cross hatched which also means "Fitted only on early models".

I will have to trace the wire that connects to post 15 to see what it connects to and then try and work out if a resistor is required (and what value).

Yet to test the 10 x 8uF 450 volt capacitors on the board.

[Craig Sawyers]

Looks a whole lot cleaner!

I had a look at farnell for 68nF 2kV ceramic capacitors - and they are now surface mount COG dielectric! That is what 60 years does to component size.

But in polypropylene film there is a 68nF 2kV cap here https://uk.farnell.com/epcos/b32654a...-pp/dp/2728553 which would need to be shoehorned in because it is again much smaller, and radial leaded.

There are axial leaded versions, but all of them (along with many other electronics parts) are on stupid lead times as a result of Covid, Not a political statement or invitation to divert into a banned topic, but just a statement of fact.

Craig

[DMcMahon]

Hi Craig, thank you for the information.

Before I read your message, I had already ordered three 0.1uF/100nF 2,000V Poly radial caps, initially not seeing any near 0.07uF/70nF & thinking that actual value not critical and probably better to go higher rather than lower.

Before throwing the old ones away, out of interest I have just wiped off the horrible sticky wax mess off 2 of them and surprised to see that they are actually 0.1uF as per photo (listed as 0.07uF in the parts listing and on the schematic).

David

[buggies]

Can't help with pin 15 as don't have circuit of the older units.
R304 was 18k 1/4w.
I have a some NOS K8-50 that you can have for cost of postage.
Checked with old wind up megger and about 10k in the good direction compared to some others which were giving 100k.

[DMcMahon]

Thank you very much George for the R304 Information, that is very helpful indeed, this is definitely not shown in my manual. When I refit the board there are about 6 wire push on spade connections that fell off when the board was disturbed including pin 15, I need to check all these to make sure I reconnect to the correct pins, so I should then see what pin 15 connects out to.

I checked my K8/50 diode resistance using push button Meggar and got between 500kohms at 50 Volts down to 100kohms at 1,000 volts, it only read in one direction so I think it maybe is OK. Still to repair the other replacement diode and will Meggar test after repair. The fact that I had a trace must mean that I had some reasonable EHT voltage.

I will PM you.

David

[buggies]

PM received and answered.

I seem to recall the wiring loom to board 3 was laced so it was difficult to connect to the wrong tag ( but not impossible...)

[DMcMahon]

Replaced the four 0.01uF/10,000pF 350 volt ceramic capacitors C314 - C317 (with 0.01uF 630 volt poly caps) on Board 3, these are used around the Focus & Brilliance pots. They were not really bad but all 4 measured around 25% low on their capacitance and were slimly and a couple of them were starting to crumble.

For a change the new replacements were larger (slightly) than the original old ones.

Thought wise to replace them while the board was out and had plenty of spares.

Tried to measure the ten 8uF 450 volt electrolytics C301 - C311 on Board 3 in-situ, but due to other connected components could not get sensible readings, so am removing one at a time and measuring. 5 done so far with good capacitance and ESR readings.

[DMcMahon]

Yes George the wiring loom is laced, so a lot of it is difficult to get wrong but especially at the bottom (where the wires fell off) not completely impossible, plus in that group of 6 at the bottom, is a wire not in the loom so depending upon which terminal pin that is fitted to it can throw some of the others out if the loose wire is refitted to wrong pin.

David

[DMcMahon]

All ten 8uF 450 volt electrolytics removed from Board 3 & tested. A tedious job and some artwork repairs required when they were refitted. I am glad now that I did remove for testing because one of them C304 is completely gone and just measures around 900pF (checked on 3 meters as did not believe it initially).

Now need to rummage through my spare capacitors to see if I have anything suitable as a replacement.

[DMcMahon]

New components arrived today so fitted.

3 x 0.1uF, 2,000VDC Poly capacitors, C306, C312 & C313, had to move a couple of the capacitor mounting terminal posts, as the new radial capacitors leads would not quite stretch across.
27k resistor to replace open circuited R312
18K resistor to replace open circuited R304
2 x 680k resistors to replace open circuited R306 & R313

Also replaced R303 18K, which measured 20k but looked very poor condition.

Also replaced R307 & R314 680K, which measured > 720K, but looked very poor condition.

Seem to have mislaid the ITT TV20-16K80V high voltage diode (in MR 304 position) that was removed during clean up, so fitted an original K8/50 that I received from buggies (George).

Started to check the push on spade wiring connections to this board and have got a bit confused as some of the wire number and connection references for the CRT connections do not appear to agree ? While checking this found some more differences between the board and the manual documentation.

The board has 2 terminals identified in the board component layout drawing as 14 but only one 14 is shown on the schematic which is the earth rail. The two 14 connections on the board are not connected together, which means that some of the components shown in the schematic connecting to earth, do not actually connect to earth, namely R312, C310 & C307. R312 for example only connects out to terminal 15, this being the same terminal that R304 connects out to (R304 previously being a mystery until its value was identified by George). Because of the confusing wiring connections (in the documentation) have not yet identified what terminal 15 connects out to.

Also see that the component layout drawing shows 9 terminal connections at the top of the board, while my board only has 8 terminals, luckily there are only 8 wires at the top section (plus one that solders to the board).

Could not find a suitable replacement for failed C304 8uF 450V so have ordered a couple.

[Chris55000]

Hi!

I've had a look through my extremely moth–eaten CD1400 book and RV304 is marked on my component layout diagram for PCB 3 (14009103) in the main unit, there's a value and type quoted for it plus setting–up instructions. RV304 is marked as a taller vertical rectangle just above the left–hand side of MR305 in the layout diagram.

R304 is referred to in my parts list as:–

"18K ¼W ±10%, Solartron Part No. 1723 41800 Erie Type 16 Carbon"

. . .and is marked on the component layout diagram as a very small hatched rectangle immediately below R312, along with Tag 15, but no pale orange lines representing the tracks are shown for either end of R304 or Tag 15, and it's not marked on either my Tech. Manual circuit, the Operating Booklet Circuit I have or the diagrams on Jon's Valve Page.

On my Operating Booklet Diagram, R309 and R315 are both marked as "330k" with additional 330k resistors R318 and R319 across R309 and R315 respectively, so Solartron may simply have fitted 150k in R309 and R315 positions – the modification adding R318 and R319 is mentioned in my parts list.

I would suspect that the left–hand end of R304 connects to the left–hand side of R312, etc., and the right–hand end of R304 leads off to Tag 15, am I correct?

The Board Assembly Removal Instructions for Board 3 make reference to 16 push–on connectors, or 17 in early models, but there's no written info on the tag wiring provided separately.

There is, by the way, hidden in the repair instructions, page 5 paragraph 32, a warning stating "components must not be unsoldered from the printed circuit", but if you have something like a Weller DSX80 or one of the "Duratool" heated vacuum desoldering–irons, you should be able to remove/desolder components if you use no more than 350–375°C or so.

Since you found R304 badly scorched/open circuit, obviously it's been passing current somewhere, but just exactly where?

My CD1400 looks like it could be fairly late production, so R304, Tag 15 and any wring to it could well have been deleted, but I'll have a check when I get time spare!

Chris Williams

[Craig Sawyers]

Yes - those single sided SRBP boards were not known for the quality of adhesion of the copper traces.

Even with single sided fibreglass it was not perfect. When I was at Wharfedale, we acquired Cambridge Audio, who used single sided FR4. The axial electrolytics used in the power supply were known to tear the copper during shipment. Overcome by a dob of hot melt to secure the component to the board during assembly.

Craig

[DMcMahon]

Thank you Chris for all the detailed information.

RV304 is not shown on my component layout drawing out, is listed in the parts listing and is shown on the schematic. So assume it was not part of the original/early design. The two 24k modern looking resistors that are fitted in place of RV304 must have been fitted at a later stage.

Yes you are correct about the R304 connections. It is shown on the component layout drawing but hatched out with no artwork connections shown, is not shown on my schematic and listed as "Not Fitted" on the parts list with no reference to its value.

I do not have the Operating Booklet. Good that your Booklet schematic shows 330k resistors in parallel with R309 & R315 (330k) so parallel combination of 165k close to my 150k values.

My board has 16 push on connections. Checking the wiring last night the missing one from the top section is # 6 which is for the Cathode Upper (KU). The soldered wire I referred to, that connects to a small pin on the board is the KU connection. Seems strange that my early version of the board did not have the 17th push on connection for KU, looks, like it was missed out on the board original artwork design !

Tag 15 is shown hatched out with no artwork connections shown on the layout drawing. I have checked out the wiring connections for the first 10 wires so 6 still to do including tag 15. There definitely appears to be errors in the numbering of the board connections at the CRT pin out, as shown on my 2 schematics which is making it slow to check fully.

David

[Chris55000]

Hi!

I will be drawing out and providing a new set of diagrams for Boards 1, 2 and 3 highlighting the various production alterations made in due course.

My manual also has two amendment sheets that are far too fragile and discoloured to attempt to scan, but I can retrieve the information from these and write them up onto new documents which will get done as soon as I have a few hours spare!

Chris Williams

[DMcMahon]

That sounds good Chris, I do not know how you will find time with all your extensive work for your planned Test Equipment & Repair book (which sounds great by the way).

I do not think my manual has any amendment sheets but will double check.

David

[Chris55000]

Hi!

Circuit diagrams, book writeups, etc., are written & drawn late at night when my landlord friend is snoring away having gone to bed and therefore not ranting at me!

Chris Williams