Further to the BWD 845.
It appears that my "lightning diagnosis" was as far off target as most such are.
I thought that it was a horizontal fault, but a bit of actual hands-on fiddling shows that if I push the "beamfinder" button, the thing will trigger & show a full width properly triggered display, so it looks like a vertical centreing problem.
My current suspicions are focused on the +15volt supply, which uses a strangely packaged regulator, & does have "form" as the previous owner had to replace the reg some years back.
The old "Bee Dubya Dee" is remarkably pretty inside, nowhere near as "fussy" as their older things like my (now deceased) BWD511, & (dare I say it) easier to find my way about in than the Tek 7613.
BWD 845
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Re: BWD 845
Manual for those playing along at home:
https://www.kevinchant.com/uploads/7/1/ ... wd_845.pdf
These use a prereg PSU like another model BWD I had years ago, nice little CRO that I don't remember the model # now.
It's fault was a shorted tant that pulled a rail down (5V IIRC) some distance along the rail from the PSU as remote decoupling in parallel with an electrolytic cap.
Simple fix.
https://www.kevinchant.com/uploads/7/1/ ... wd_845.pdf
These use a prereg PSU like another model BWD I had years ago, nice little CRO that I don't remember the model # now.
It's fault was a shorted tant that pulled a rail down (5V IIRC) some distance along the rail from the PSU as remote decoupling in parallel with an electrolytic cap.
Simple fix.
Siglent Distributor NZ, TE Enabler
Re: BWD 845
My second hunch didn't pan out much better than the first, as all the power rails are there, so I had to drag out the "big guns" in the shape of the little Digitech analog CRO (the one that looks like it was designed to be used by Cabbage Patch Kids).
Chasing through the vertical amplifier chain, most stages were pretty close to the values on the schematic, so I ended up sniffing around the two transistors that drive the vertical plates, & their drivers.
The drivers are on one board, with the output stages on their own, separate board.
Looking closer at it, I think there is a nice dry joint where R234 connects to a standoff (or it might be R235, apparently those resistors have given trouble in the past & the replacements being larger, don't quite line up with the PCB markings.)
I decided to leave it till tomorrow, as my aches & pains were starting to kick in, & as I reasoned, "I'm not getting paid for this!"
Chasing through the vertical amplifier chain, most stages were pretty close to the values on the schematic, so I ended up sniffing around the two transistors that drive the vertical plates, & their drivers.
The drivers are on one board, with the output stages on their own, separate board.
Looking closer at it, I think there is a nice dry joint where R234 connects to a standoff (or it might be R235, apparently those resistors have given trouble in the past & the replacements being larger, don't quite line up with the PCB markings.)
I decided to leave it till tomorrow, as my aches & pains were starting to kick in, & as I reasoned, "I'm not getting paid for this!"
Re: BWD 845
Certainly an unusual setup with 6x 330R in series.
If some have been replaced you might do well to replace the lot.
If some have been replaced you might do well to replace the lot.
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Siglent Distributor NZ, TE Enabler
Re: BWD 845
It actually makes a lot of sense. The final amp will be operating in the linear region so there's going to be some power dissipated across those. That means you can use cheaper resistors, which are smaller and have less inductance. Also the parasitic capacitance is all in series so it's less than one big one.
Also 2N2219 as a plate transistor. Sneaky.
Also 2N2219 as a plate transistor. Sneaky.
Re: BWD 845
I'm getting to know old "Dubya" more intimately than I ever wanted to.
When I went out the back to feed the furry mob, whilst waiting for George (the dog, not the POTUS) to come in from his vital "George game", which seems to consist of running, stopping, running back to where he started, woofing then repeating the process, I had a look at those resistors with the Ohms range of the Fluke 77.
It looks like the resistor connection that visibly appeared to be a dry joint is maybe just a very "flux-covered" joint, as the connections look to be intact, & the resistance values right.
I was working on the hypothesis that one vertical deflection plate was getting a reduced or no signal, so the beam was deflected off screen, but reading how the beamfinder (which does work) is supposed to work casts suspicion upon other things, like, maybe blanking.
BWD really likes switches with multiple sections, so if one section removes blanking when that button is pushed, making the trace visible, perhaps I have been "chasing my tail".
If nothing else comes up, I will dig further into the beast today.
When I went out the back to feed the furry mob, whilst waiting for George (the dog, not the POTUS) to come in from his vital "George game", which seems to consist of running, stopping, running back to where he started, woofing then repeating the process, I had a look at those resistors with the Ohms range of the Fluke 77.
It looks like the resistor connection that visibly appeared to be a dry joint is maybe just a very "flux-covered" joint, as the connections look to be intact, & the resistance values right.
I was working on the hypothesis that one vertical deflection plate was getting a reduced or no signal, so the beam was deflected off screen, but reading how the beamfinder (which does work) is supposed to work casts suspicion upon other things, like, maybe blanking.
BWD really likes switches with multiple sections, so if one section removes blanking when that button is pushed, making the trace visible, perhaps I have been "chasing my tail".
If nothing else comes up, I will dig further into the beast today.
Re: BWD 845
Have you checked TP 2&3 for equivalent signals ?vk6zgo wrote: ↑Wed Sep 06, 2023 12:02 am It looks like the resistor connection that visibly appeared to be a dry joint is maybe just a very "flux-covered" joint, as the connections look to be intact, & the resistance values right.
I was working on the hypothesis that one vertical deflection plate was getting a reduced or no signal, so the beam was deflected off screen, but reading how the beamfinder (which does work) is supposed to work casts suspicion upon other things, like, maybe blanking.
If they are then the problem is in driver or output stages......wouldn't be the first time I've seen any of those transistors fail.
Siglent Distributor NZ, TE Enabler
Re: BWD 845
After boning up on the workshop manual, I spent a bit of time measuring the values of various resistors on Drawing 1406.
They all seemed to be pretty close to correct, so I fired the 845 up & checked the various DC voltages, which all seemed to be around the right figure (where it was given & what I guessed where it wasn't).
The waveform appearing as (1) on the previous page was shown as having a DC component of -600v.but I couldn't see where that would come from.
(1) is on pins 9,11 & 13 of U501 (a CA3046), & there were no components in the area which looked like they could survive -600v, nor would such a voltage make sense in the circuit operation.
The DC voltage was around 0.7v, which made much more sense.
Dragging out the "Cabbage Patch CRO", I looked at the waveform, which quite dissimilar to the one shown.
I tried various functions like ALT & CHOP, but no difference.
Around this time, I looked at the front, & lo & behold, a great big, fat, sassy trace!
I looked at the Digitech 'scope's CAL signal with the 845, & there it was, everything "up & running", with no idea of why! -----Don't you just hate that?
I messed around, trying to get it to fail, but to no avail!
After turning it off & on a few times I couldn't fault it, so I left it off for an hour, then turned it on.
The damn thing came back sweet as pie!
At least while it is working, I can check the various waveforms & see where BWD were "lying in their teeth".
I can't see anything wrong with using the BWD to "look up its own bum", as the little CRO won't photograph as well.
I will then hit various spots with the heat gun, & if that doesn't faze it, I'll button old "Dubya" up----that should do it if anything will.
If it still Ok, I have plenty of jobs waiting for its attention, including the 7613.
They all seemed to be pretty close to correct, so I fired the 845 up & checked the various DC voltages, which all seemed to be around the right figure (where it was given & what I guessed where it wasn't).
The waveform appearing as (1) on the previous page was shown as having a DC component of -600v.but I couldn't see where that would come from.
(1) is on pins 9,11 & 13 of U501 (a CA3046), & there were no components in the area which looked like they could survive -600v, nor would such a voltage make sense in the circuit operation.
The DC voltage was around 0.7v, which made much more sense.
Dragging out the "Cabbage Patch CRO", I looked at the waveform, which quite dissimilar to the one shown.
I tried various functions like ALT & CHOP, but no difference.
Around this time, I looked at the front, & lo & behold, a great big, fat, sassy trace!
I looked at the Digitech 'scope's CAL signal with the 845, & there it was, everything "up & running", with no idea of why! -----Don't you just hate that?
I messed around, trying to get it to fail, but to no avail!
After turning it off & on a few times I couldn't fault it, so I left it off for an hour, then turned it on.
The damn thing came back sweet as pie!
At least while it is working, I can check the various waveforms & see where BWD were "lying in their teeth".
I can't see anything wrong with using the BWD to "look up its own bum", as the little CRO won't photograph as well.
I will then hit various spots with the heat gun, & if that doesn't faze it, I'll button old "Dubya" up----that should do it if anything will.
If it still Ok, I have plenty of jobs waiting for its attention, including the 7613.
Re: BWD 845
I'd guess it's a dry joint or a dodgy connector.
I bought a 100MHz Hameg for next to nothing, being told that it didn't work and couldn't produce a trace. I took it home and tried it and sure enough, it didn't produce a trace, exactly as I'd been told. I removed the cover to check for anything missing, burnt or damaged, and check the voltages. All seemed OK. The room was fairly dark and I thought I saw a trace off the screen. I tried the Y position adjustment and the trace was on the screen. Then I tried with a probe and it produced the display I'd expect from the calibrator. I've tried it a dozen times since then, with and without the cover, and it just powers up as it should.
It's hard to know whether to be annoyed or pleased when that happens. On the one hand the scope works, so there's probably no gross fault such as the CRT or a transformer. On the other hand, you don't know why it stopped working or why it started working, and it could kick off again.
I bought a 100MHz Hameg for next to nothing, being told that it didn't work and couldn't produce a trace. I took it home and tried it and sure enough, it didn't produce a trace, exactly as I'd been told. I removed the cover to check for anything missing, burnt or damaged, and check the voltages. All seemed OK. The room was fairly dark and I thought I saw a trace off the screen. I tried the Y position adjustment and the trace was on the screen. Then I tried with a probe and it produced the display I'd expect from the calibrator. I've tried it a dozen times since then, with and without the cover, and it just powers up as it should.
It's hard to know whether to be annoyed or pleased when that happens. On the one hand the scope works, so there's probably no gross fault such as the CRT or a transformer. On the other hand, you don't know why it stopped working or why it started working, and it could kick off again.
Re: BWD 845
Yep that.
Byran, is CA3046 socketed ?
Might pay to reseat all/any devices that are.
Siglent Distributor NZ, TE Enabler
Re: BWD 845
Yes, it looks like all the ICs are socketed, so that is, in a way, a bonus.
Funny thing, I keep finding an IC puller amongst my junk, which disappeared for years when I would have used it, but now, from time to time, comes along & "nudges" me.
I better put it with the BWD hardware, so it doesn't hide again.
I typed a long, rambling screed (as is my wont) earlier, then W10 decided to crash the display to half size, & in the ensuing search for a fix, I lost everything I had written---- probably just as well!
"Dubya" has had a night off for the fault to come back, so I will trot out to the Lab/Ham shack/storeroom/dog room/cat room & try it again.
Funny thing, I keep finding an IC puller amongst my junk, which disappeared for years when I would have used it, but now, from time to time, comes along & "nudges" me.
I better put it with the BWD hardware, so it doesn't hide again.
I typed a long, rambling screed (as is my wont) earlier, then W10 decided to crash the display to half size, & in the ensuing search for a fix, I lost everything I had written---- probably just as well!
"Dubya" has had a night off for the fault to come back, so I will trot out to the Lab/Ham shack/storeroom/dog room/cat room & try it again.
Re: BWD 845
I now remember a similar fault in a Telequipment D83, in which every active device was socketed and while reseating them a lead fell off a bipolar, a ZTX500 IIRC which hadn't been available new for ages but successfully replaced with a modern equivalent.
Siglent Distributor NZ, TE Enabler
Re: BWD 845
The beastie hasn't shown any sign of the original fault, so I was playing around with it, & noticed that the delayed/dual timebase isn't working correctly, in that winding the delay multiplier doesn't shift the intensified part of the displayed waveform in the "A intensified by B" position.
Initially, I thought I was just unfamiliar with how BWD do things, but probing around with the little CRO, I determined that turning RV404 on DRG.1404 across its range changed the gate voltage of Q405, but did nothing on its source or pin 3 of U404.
As the JFET is part of an unobtainium Twin FET package, that was a bummer, but digging around amongst my junk, I found a scabby old 8 pin DIP header & some MPF102s & slapped a "bodge" together.
Now, I have a variable voltage on pin 3 of U404, but still no change of the intensified display section.
I can get U404 from DigiKey, but I'm not really certain if that, too is faulty.
At this point, I decided to try my usual trick when device information becomes vague,: -"See how Philips do it!"
Unfortunately, Philips "do it" in a completely different manner, as do Tektronix, so I'm "on my own"!
The little Digitech, although doing valiant service displaying the various waveforms is only single channel, where I really need to compare two waveforms, & apart from that, the BWD manual waveforms don't look like the ones I'm getting, so at this point, I'm going to "button the thing up".
Even without delayed timebase & with a "phantom" possibly recurring fault, it is still a very capable 'scope.
Initially, I thought I was just unfamiliar with how BWD do things, but probing around with the little CRO, I determined that turning RV404 on DRG.1404 across its range changed the gate voltage of Q405, but did nothing on its source or pin 3 of U404.
As the JFET is part of an unobtainium Twin FET package, that was a bummer, but digging around amongst my junk, I found a scabby old 8 pin DIP header & some MPF102s & slapped a "bodge" together.
Now, I have a variable voltage on pin 3 of U404, but still no change of the intensified display section.
I can get U404 from DigiKey, but I'm not really certain if that, too is faulty.
At this point, I decided to try my usual trick when device information becomes vague,: -"See how Philips do it!"
Unfortunately, Philips "do it" in a completely different manner, as do Tektronix, so I'm "on my own"!
The little Digitech, although doing valiant service displaying the various waveforms is only single channel, where I really need to compare two waveforms, & apart from that, the BWD manual waveforms don't look like the ones I'm getting, so at this point, I'm going to "button the thing up".
Even without delayed timebase & with a "phantom" possibly recurring fault, it is still a very capable 'scope.