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Old 12th Jan 2018, 9:45 pm   #1
Analog Dave
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Default New member and a Telequipment D54

Hi folks

I'm a new member with a new to me Telequipment D54. I have been restoring vintage organs-Hammond Tonewheel, Farfisa Compact transistor etc and vintage tape and wire disc echo machines for years as a collector and hobbyist and have finally got around to searching for a suitable oscilloscope. I wanted something analog from the era that my gear comes from.

I bought the D54 knowing that it might need some work and with the risk that something non-replaceable might be toast such as the CRT. I also have no experience with scopes but I am used to working on dangerous high voltage tube amps.

Having gone through the calibration process in the service manual the problem has become evident. The CRT works and I can set up the position of both channels but the time base control has no effect. Both dots disappear when switched away from the Ext X setting. There is no movement. When I apply signal to a channel there is a thin vertical modulating line but it does not move. All other controls appear to work with position, size, gain, contrast etc.

As with all of my gear I will go through and replace all of the electrolytic caps including the power supply caps but then what?

In the days to come I am hoping that one of you may be able to help me understand how the time base circuit works to help me work this out with logic and elimination.

Best
Dave
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Old 13th Jan 2018, 7:01 am   #2
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Default Re: New member and a Telequipment D54

Welcome t' forum Dave. Most of the big electrolytics will probably be ok so a mass change of caps may not fix your problem or make the situation worse. Not familiar with this scope but hopefully someone will. It's a good idea to post the schematic of the relevant circuit, you get more answers. Manual here - http://www.eserviceinfo.com/download...pment_D54.html

Andy.
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Old 13th Jan 2018, 7:41 am   #3
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Default Re: New member and a Telequipment D54

First things first: how do you have the triggering controls on the timebase set? There are many combinations of settings that won't allow the timebase to run. I don't know the D54 specifically, but look for the words 'INT' and 'AUTO' and select those. Does the timebase run then?

Chris
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Old 13th Jan 2018, 9:20 am   #4
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Default Re: New member and a Telequipment D54

My Telequipment 'scopes suffered from EHT resistor chain faults, and bad contacts on plug in transistors. Had no capacitor faults, you may make matters worse just changing them.
I was greatly helped by "mhennessy" on this forum who knew some of the qwerks.
They are a pig to work on, access to both sides of the pcbs at the same time is impossible.
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Old 13th Jan 2018, 12:07 pm   #5
Analog Dave
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Default Re: New member and a Telequipment D54

Hi friends

Thank you for so many replies in quick succession! I'm glad this is such a lively forum and I wish I had found it before.

I take on board your advice about the electrolytics and will leave them unless I see any bulging ones. My electronics background has been mainly in audio as I mentioned before and for tonal quality or tuning stability there is a lot of emphasis on replacing them.

I have a copy of the manual kindly posted above and carried out the "first time" procedure as described at the beginning.

Something I neglected to mention in my first post is that when the unit is first turned on from cold (after 24 hours of non use) I get a little activity from the first couple of settings on the time base control. This doesn't last more than 30 seconds. The dots will move across to the middle of the screen from the left and vanish. On the next setting it is faster and then nothing else happens. I am assuming that something is warming up and then failing. I have had this on my combo organ where a transistor will go out of tune after a couple of minutes.

I would like to try and figure out the transistors that are part of the timebase circuit. Maybe I can freeze spray them to identify a bad one or replace them shotgun style. I am fortunate to work near a company called Langrex in Billingshurst, West Sussex who have been a great supplier of vintage components in the past.

I will get it opened up in my workshop today and start probing.

I did notice a helpful post on this forum last night through a google search that was talking about a different Telequipment model that was prone to cracking resistors and am wondering whether my model is likely to suffer this too.

Many thanks again for your interest.

Best
Dave
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Old 13th Jan 2018, 12:39 pm   #6
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Default Re: New member and a Telequipment D54

They all suffer from resistor failures, especially the high voltage ones. That timebase behaviour is familiar, I think it is connected with the supplies developed from the EHT box that feed the timebase. May be wrong, its been a while.
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Old 13th Jan 2018, 1:44 pm   #7
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Default Re: New member and a Telequipment D54

Have a look at Mark Hennessy's web site, there is info on Tele scopes.
https://www.markhennessy.co.uk/
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Old 13th Jan 2018, 4:51 pm   #8
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Default Re: New member and a Telequipment D54

Telequipment D54. Nice machine, dual trace, 10Mhz, with a very good Brimar tube D13-47. Worth getting going. I'd endorse what the others say.

But even more first, check out all the voltage rails. Should be within +-10% at this stage. As it appears to be largely working, leave electrolytics alone. They are often a higher grade in test gear than in consumer equipment.

The EHT resistor chain is a well known weak spot on later Telequipment (Tektronix) scopes (D63,D75,D83), but this one has a mains powered EHT, lower value resistors and less voltage stress across them. and you have a trace, so leave R302-305 alone.
You appear to have a Y trace.

Have you an external X trace: feed in the calibrator to get a horizontal line, and can you shift and expand it (X shift and X gain controls). That confirms the X Amplifier. Though the initial spot only moving half the screen suggests half the X amplifier has failed. Easy to identify, just check voltages across X amplifier loads R175,R179. Leave that for now and get the TB working first.

So now look at where the main trouble sounds to be: Trigger, or the Timebase itself.
Trigger is a traditional trouble spot with early Telequipment scopes, but this one appears a Tektronix design after the take-over, which are usually better.
Check control settings, Normal/Int with Y1 signal input, Y1 on, Y2 off, TrigCh1. Set Trigger Level to Auto and Stability to fully CW. Then try with Trigger Level central and play with Stability. Those should give a horizontal sweep.
If not, clean all Trigger and TB switches.
The negative voltages mentioned shouldn't be a problem on this model. It is not a separate feed from the EHT supply, as in some earlier Telequipment scopes, jsy off the -12v rails.

Transistors. I have found the Motorola pnp MPS6518 a bit unreliable. I have had much trouble with them in a couple of D67, where substitution proved a quick solution. Almost any small general purpose pnp eg. BC388/BC212/BC307 will do. It doesn't matter if it is not quite the same specification, as long a voltage rating is enough, as you want to get the thing working now.
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Old 13th Jan 2018, 7:27 pm   #9
Analog Dave
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Default Re: New member and a Telequipment D54

Thanks all for the continued support. I haven't got her on the bench yet, it will be tomorrow.

However I have tried Bill's advice and connected my signal generator to Ext X and have a horizontal trace that is adjustable in length and position. Again - as soon as I turn the timebase control away from the Ext X setting I lose everything off the screen.

Does this narrow things down a little?!

Dave
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Old 13th Jan 2018, 9:32 pm   #10
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Default Re: New member and a Telequipment D54

This sounds a bit like an unblanking problem to me.
A WME-Bill said, make sure STABILITY is set fully over to ensure trace will run. You see some initial timebase display, but it then disappears. Set your timebase speed very slow, say 0.1 secs per division. Connect a voltmeter, PREFERABLY ANALOGUE**, between one X-plate connection (collector of TR113 or TR114. You should see the pointer go from 0 to to about 50v, then quickly back again. Similar on each X output point. If that is happening, but you see nothing happening on the screen, then the X amp is OK, but the unblanking is not. Check TR109, Tr111 and TR115, replacement being easy as Bill said.
**If you don't have an analogue meter, set timebase speed to 1sec/div, and MAYBE a DVM will show the same, but it will take 10 seconds to rise fron 0v to 50v.
Les.
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Old 13th Jan 2018, 10:22 pm   #11
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Default Re: New member and a Telequipment D54

Quote:
Originally Posted by Analog Dave View Post
Something I neglected to mention in my first post is that when the unit is first turned on from cold (after 24 hours of non use) I get a little activity from the first couple of settings on the time base control. This doesn't last more than 30 seconds. The dots will move across to the middle of the screen from the left and vanish. On the next setting it is faster and then nothing else happens. I am assuming that something is warming up and then failing. I have had this on my combo organ where a transistor will go out of tune after a couple of minutes.
Don't be mislead by this - it might just be the effect of caps charging initially, rather than any real life in the timebase. Had you seen a few complete scans, that would be a different matter.
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Old 14th Jan 2018, 2:19 pm   #12
Analog Dave
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Default Re: New member and a Telequipment D54

Just a quick update, on opening her up I found C409 15uf/450 had leaked electrolyte, so have ordered three to replace the row of them.

Turning to the transistor replacement, can you believe that every si transistor in my stash is an NPN rather than the PNP called for here. I have ordered some BC 388's to try.

I cleaned the timebase and trigger controls with Servisol 10 but this made no difference.

I would like to check the power rails next but am unsure where to take my reading from.

Best
Dave
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Old 14th Jan 2018, 6:31 pm   #13
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Default Re: New member and a Telequipment D54

PNP transistors have not been "Called for". WME-Bill mentioned that the mps6518 frequently used by TQ can be faulty. I specifically mention transistors in the X output and unblank sections, all of which are NPN.
Don't assume only PNP types used.
Les.
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Old 14th Jan 2018, 6:51 pm   #14
Analog Dave
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Default Re: New member and a Telequipment D54

Sorry I'm not sure how I made my mistake Les.

I looked at the Datasheet for the BC008 transistor that Bill suggested and it was a PNP. I didn't think that I could swap a PNP for an NPN. When I said "called for" I was only talking about the three transistors that Bill said I should check.

Over the years I have heard techs use the term "called for" as in "the schematic calls for a 100R resistor" or some such.
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Old 14th Jan 2018, 9:41 pm   #15
Analog Dave
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Default Re: New member and a Telequipment D54

I ought to ask for some safety advice before diving into this scope. On my audio/music equipment I am aware of where the high voltage is and where the low voltage is but I have never worked on anything with a CRT. I know how to discharge caps on tube amplifiers but that is where my flirting with danger ends.

If I have to remove the circuit board in my scope for component replacement or even just to lift resistors, are there any precautions I have to take? Is the CRT HV safely contained within it?

Thanks
Dave
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Old 15th Jan 2018, 7:24 am   #16
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Default Re: New member and a Telequipment D54

Treat the CRT as a big valve, it has a heater, anode, cathode, and grids just like an EL84 or ECC83 so no EHT is stored.

Most analogue scopes have positive and negative rails in relation to ground. Most of the rails are measurable with a 1000v DC DMM apart from the cathode ( over -1000v DC ish ) the anode is usually about + 700 - 900v , again ish. The CRT heater winding is usually center tapped and referenced to some high negative voltage, usually the cathode.

But as your scope uses tranny's and not valves and you know the CRT is ok, you can leave the scary rails be. All you have to be aware of is caps holding charge, which you know about.

Andy.
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Old 15th Jan 2018, 5:03 pm   #17
Analog Dave
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Default Re: New member and a Telequipment D54

Thanks Andy! I want to get the board out ready for the replacement of C409 -412. I might as well replace the other few board mounted caps while I have it loose. The chassis mount ones look fine.

Last night I found another D54, scruffy with a dead CRT for 20 and free postage on ebay so have snagged it in the hope that I can swap out the transistors and hopefully get my timebase/trigger working.

Best
Dave
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Old 15th Jan 2018, 9:59 pm   #18
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Default Re: New member and a Telequipment D54

A CRT is not really "just a big valve". There is around 2+ KV at the hot end and -1KV at the other end, and scope tubes, like TV tubes can hold enough volts to wake you up.
Just take care, and don't pull out any boards without very good reason.
Some scopes can have 20KV from one end to the other!
Les.
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Old 16th Jan 2018, 8:58 pm   #19
Analog Dave
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Thanks Les!

Well I tried to remove the board last night but couldn't. The wires to the back of it were too tight. I was going to connect the new caps to the legs of the old caps after removing the bodies of the three caps that were leaky.

However the second "parts" D54 I mentioned above was here when I got home and although the channel 1 Volts/CM switch is damaged, the unit works fine! So my original unit will become the parts doner. At least I know everything works apart from the time base and I can swap over the channel 1 rotary switch at some point. I am still tempted to get to the bottom of the timebase problem as it would be a good learning exercise!

Still at least I can start those repair jobs that need a scope now!

Thanks everyone.
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