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2467B No B Sweep
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Hey All,
I've managed to find some time to play with my 2467B and have been trying to untangle whether the non-working CTT option (CT TEST 86 FAIL 02) has broken the B sweep or if the B sweep itself isn't working at all. Regardless of whether B "RUN AFT DLY" "TRIG AFT DLY" or "TRIG Delta DELAY" is selected, I see "MISSING B TRIG" on screen. I reckon "TRIG AFT DLY" shouldn't work at all since this is what's indicated isn't working by TEST 86 FAIL 02. So here's what I observe. I get a stable trace using the A sweep. I pull the SEC/DIV knob, turn it one click to the right, and push it back in to switch to the B sweep. I then observe no trace at all, for any position of the holdoff knob, for any value of the DLY value on screen, and for any B trigger setting. This scope is pretty complex and I understand I might just not be using the B sweep correctly... but if indeed this is abnormal behavior, how can I tell if the CTT failure is causing this, or if it's something related to the A/B trigger hybrid, B sweep hybrid, or display sequencer IC? Or perhaps something totally unrelated? Does anyone have any experience with this behavior? |
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Okay following the video of w2aew (), I'm now a bit more confident I'm not goofing something up. Pulling the SEC/DIV knob doesn't result in an intensified region, and turning the knob doesn't result in a second trace. I think the B sweep is just out.
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On Mon, Mar 18, 2019 at 09:05 PM, <thespin@...> wrote:
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It¡¯s not. The proper lights come on suggesting the scope is trying to run the B sweep, but it isn¡¯t running.
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On Tue, Mar 19, 2019 at 06:57 AM, Manuel Maseda wrote:
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You could try swapping the A and B sweep generator hybrids U700 and U900, they are identical part numbers. There should be some recommendations here about cleaning the contacts (carefully!) if the present U900 is at fault. The sweep generator hybrids are relatively low prices on the spares market which suggests they don't fail very oftem!
Roger |
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On Tue, Mar 19, 2019 at 8:54 AM <thespin@...> wrote:
It¡¯s not. The proper lights come on suggesting the scope is trying to runI would start by pulling, cleaning and re-seating U900. Second perhaps swap U900 and U700. If that doesn't help, you might be able to narrow this down a bit by experimenting with various A/B sweep speed combos and B delay/trigger settings. If there's any combo that will produce a sweep, then you can start eliminating problems. If there's no combo that'll start the sweep, then I'd focus on the constant current generator op-amp (U910A in my 2467 schematic), and then on the delay ref outputs from the A5 board. |
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I've tried cleaning U500 and U900 to no avail, and then I swapped U900 and U700 again to no avail. Will continue searching for sweeps that might work and looking at that opamp.
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On Tue, Mar 19, 2019 at 01:15 PM, Siggi wrote:
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Incidentally, it may help to understand what's inside the hybrid. If you're
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wondering, take a look at page 6-59 of this document < >. There's a fair bit of "stuff" in there (that I haven't studied in detail). On Tue, Mar 19, 2019 at 7:20 PM <thespin@...> wrote:
I've tried cleaning U500 and U900 to no avail, and then I swapped U900 and |
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On Tue, Mar 19, 2019 at 7:20 PM <thespin@...> wrote:
I've tried cleaning U500 and U900 to no avail, and then I swapped U900 andIt's probably worth mentioning that unless you're planning on re-calibrating the scope, you'll want to swap the sweep hybrids back. Part of the calibration is to compensate for R/C on-hybrid component variances. |
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1. No sweeps seem to work
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2. The opamp outputs look close enough that I'm inclined to assume they're doing their job 3. THO on U900 appears stuck high for all front panel configurations I could test. It dips low momentarily when turning the sec/div knob, but shows no periodic behavior. On Tue, Mar 19, 2019 at 07:20 PM, <thespin@...> wrote:
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I¡¯d look at the A5 timing reference signals next. Those go to DR of U700
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and get compared with the ramp voltage to gate the B sweep. On the A5 board they¡¯re DLY REF 0/1. NB: did you try dual delay sweeps? I believe that mode will use only the A sweep, but alternate the delay between the two control voltages, allowing you to see whether the controls are responsive. On Tue, Mar 19, 2019 at 19:56 <thespin@...> wrote:
1. No sweeps seem to work |
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Chuck Harris
Was this the 2465B that had the CTS installed? If so, pull all the
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plugs, and install jumpers on J102, pins 3&4, 1&7, and J101 pins 1&3, 6&8. The sweep won't work if those paths aren't connected... for whatever reason. -Chuck Harris Siggi wrote: I¡¯d look at the A5 timing reference signals next. Those go to DR of U700 |
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Pulling the relevant cables and adding the jumpers didn¡¯t seem to help. Will proceed by measuring all the relevant triggering lines and trying to figure out what¡¯s holding the sweep back from happening. But nobody has seen this sort of problem where there¡¯s no B sweep and assigned blame to one of the hybrids or the display sequencer or one of the surrounding components?
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On Wed, Mar 20, 2019 at 07:44 AM, Chuck Harris wrote:
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I haven't seen this failure here before, but if your timing reference
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signals from the A5 board get turfed, your B sweep would never start. It could be whole lot of other things, I'm sure, but A5 failures are endemic on these scope, easy to diagnose and inexpensive to fix. I'm told it's good practice to look for horses before zebras... On Thu, Mar 21, 2019 at 7:28 AM <thespin@...> wrote:
Pulling the relevant cables and adding the jumpers didn¡¯t seem to help. |
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Chuck Harris
I'm sure I have, but I don't specifically remember it.
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The sweep hybrids are solid, very few problems. However, the trigger hybrid is not, it is used heavily, and there are lots of problems with it.... particularly in CTS scopes... as the trigger hybrid is the basis of all CTS measurements. Everything in this scope is fly-by-wire. The DAC does yeoman's duty with all its use servicing sample and hold cells, and as an ADC, in conjunction with the trigger hybrid. 4051 MUX's fail regularly, as do the opamps in the sample and hold cells... and be suspicious of any CA3046's, or 3346's. on occasion one of the sample and hold storage capacitors will get leaky. -Chuck Harris thespin@... wrote: Pulling the relevant cables and adding the jumpers didn¡¯t seem to help. Will proceed by measuring all the relevant triggering lines and trying to figure out what¡¯s holding the sweep back from happening. But nobody has seen this sort of problem where there¡¯s no B sweep and assigned blame to one of the hybrids or the display sequencer or one of the surrounding components? |
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On Thu, Mar 21, 2019 at 9:48 AM Chuck Harris <cfharris@...> wrote:
4051 MUX's fail regularly, as do the opamps in the sample and holdI also remember a case where a decoupling capacitor on the mainboard side of one of the A5 control lines went leaky and pulled the control signal down. |
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DLY REF 0/1 also control the position of the vertical cursors, right? These function just fine, so I don't think it's these control lines.
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On Thu, Mar 21, 2019 at 10:13 AM, Siggi wrote:
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The 2465B has a separate CURSOR 0 line, but DLY REF 1 is shared. I think
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this was done to allow cursors under delay sweeps. I'd guess DLY REF 0 controls the B-sweep timing, so I'd take a gander in your shoes. On Thu, Mar 21, 2019 at 11:07 AM <thespin@...> wrote:
DLY REF 0/1 also control the position of the vertical cursors, right? |
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Okay one more question before I dig in. How is the trace A brightness intensified when you first pull the SEC/DIV knob? I assume somehow through U650. How does it know when to kick the trace brightness up a little over the region which will later be focused in on? I assume there's some comparators somewhere.
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On Thu, Mar 21, 2019 at 11:19 AM, Siggi wrote:
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On Thu, Mar 21, 2019 at 12:26 PM <thespin@...> wrote:
Okay one more question before I dig in. How is the trace A brightnessPer the service manual, page 3a-18: "To produce the intensified zone on the A Sweep trace for A intensified by B Sweep displays, an additional current is added to the crt drive signal by the Z-Axis Amplified during the concurrence of the /SGAZ and /SGBZ (sweep gate A and B z-axis) signals." If you think about it for a spell, it makes sense for this to be a function of the sweep gate signals, because of the complexity that goes into the timing of the sweeps. If you've ever played with a triggered intensified B-sweep, you'll know how it jumps around with the B-trigger position. On these scopes you can view the A and B sweeps simultaneously, with the B sweep intensified on the A sweep, and then again with a separate trace for the B sweep. This takes two total sweeps, one for each trace, with alternate sweep generators coupled to the horizontal amplifier. I've never tried to verify this, but I expect you'll see both the A and B gate signals change on every sweep when the B-sweep is engaged, whether the A or B or both are on display at the time. Good luck, Siggi |
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