Telequipment S61 triggering problems

[MrBungle]

I have a problem with a recently acquired Telequipment S61. It mostly works and smells slightly less horrible after some judicious cleaning of the wafer switches and chassis but it doesn't trigger reliably all the time. Various attempts to locate a service manual have also been unsuccessful and finding any similarity between the D61A units and this. Does anyone know where I can locate a manual for this or shed some light on the relationship to other models. Any help appreciated.

[Cobaltblue]

Hi as far as I know you can download the S61 and S61A info from here
http://elektrotanya.com/telequipment.../download.html

Good luck!

Cheers

Mike T

[MrBungle]

Excellent thank you very much - I had no idea that site even existed.

A quick scan reveals an interesting problem. Mine has two separate transformers in it whereas the schematic only shows the main power transformer. Very odd.

[micheal]

http://elektrotanya.com/telequipment.../download.html

This site only offers D61A circuit, which is totally different to the S61, as
far as i know the S61 is not available as a free download on the webb

[MrBungle]

Indeed. I noticed that earlier.

The main board appears to have the same layout however and there is space for a second channel in the chassis. I suspect it's a cut down D61A. I will proceed on this basis and see where I get and write it up for anyone else who comes across one of these. Might take a week or two!

[karesz*]

Micheal;
you can see in "my attached" doc, that its for S61B, and (only)parts of the circuit are marked as "D61"...
Btw; its a source (maybe) for S61A SM at $3.99_hopfelly. Or after registration, must be free from here...
Karl

[MrBungle]

From what I can tell there was only one S61.

The manuals listed are all for D61 units with no mention of the S61. The one on servicemanuals.mobi has a picture of a D61 on the front unfortunately. I think this scope is an awkward one.

I took a detailed look at it last night and roughly traced the timebase and triggering circuit and it based on the same design as the D61 with a very different board layout. I have isolated the purpose of the second transformer. It turns out to just supply the two main analogue rails and the other transformer does the HV and deflection voltages but I didn't poke it as I don't have an HV probe set available.

On a positive note, I hooked up my other scope to it and watched the trigger pulses and noticed that it wasn't triggering correctly on certain timebase positions. A quick poke at the contacts with a tweaker and triggering works better but there is a huge amount of noise. That suggests the wafer switch, despite cleaning, is completely knackered. The rings are all clean so this is probably the contacts themselves. I will extract one, a mammoth task looking at it, and see if I can find a replacement or refurbish it.

If that fails, I shall eviscerate the timebase and controls and use it as X-Y display and as an enclosure for my eternally incomplete spectrum analyser.

[micheal]

Karl,
as far as i know the S61 was only made as S61 no A or B, but i stand to be
corrected, and of coures it's only 5megs bandwidth. Mike

[MrBungle]

I think 5MHz was pushing it. I can see the -3dB at around 4MHz at the moment but this might be calibration issues. At least there's no problem with 1x probes knocking the bandwidth out

[MrBungle]

I've taken some photos for reference as people might find it useful if they come across one of these.

Firstly we have the vertical section, which is about as cheap as they could muster. The left section appears to be (left to right), a power supply followed by differential amplifier (assume main vertical) followed by another diff amp (trigger I think) and attenuators and compensation:



The rear has nothing exciting other than some cringeworthy use of flat 300 ohm transmission line.



The main board is slightly more interesting. From left to right timebase, CRT amp, HV section, mains input filtering and voltage selection.



Pretty much as cheap a scope as they could make I reckon!

[MrBungle]

A late reply. I fixed this. There was a resistor that had drifted out of tolerance. Was the LAST one I desoldered and tested. But I won the battle.

[micheal]

Well done what is it's circuit reference?

[MrBungle]

I don't know what the circuit reference was - I couldn't locate it in any schematics due to the disparity of the S61 and D61 models. It was on the timebase control wafer switches and wasn't part of the main timebase oscillator.