Anyone know if there is a solution to low display brightness on a HP 54111D oscilloscope, like maybe power supply capacitor replacement?
The CRT power supply voltage described in the service manual is puzzlingly-low...only 120 VDC (?!?) The 300V switching supply is described as used for generating the 5V logic supply.
I haven't dug further, but wonder how a color CRT can get by with such a low voltage...or if the CRT module has an integral flyback supply for anode voltage, and repair being module-focused, isn't discussed.
The CRT thought led me to wondering if CRT rejuvenation was an option.
I overly simplified the comments on the power supply which was evidently mo re confusing than accomplishing a summary.
Based on the service manual?s description of how the voltages are p roduced, I offered two distractions. The overview described the +300 V supp ly as being used for producing the +5 VDC logic supply and the CRT supply a s they name it is only +120 VDC. I didn?t mean to sound like only m easures 120 instead of 300.
There was an implied question-how the heck do they run a CRT on 120 VDC? I didn?t (yet) see further explanation of internal functions on the C RT ass?y. I hope it?s an assembly with the ability to produ ce all support voltages for a CRT.
The diagnosis for CRT problems, as well as other modules, often ends with ?replace the module?...I get ?why??, during the product?s heyday, but that leads to a ?problem? ? period (for wannabe users/restorers) in the future...which is now.
I haven?t measured anything yet...it?s usable, but I? ?m just snooping around for answers for that day when all the room lights have to be off to see anything. If I?m going to commit space to su ch a large (and loud!) I?m trying to be proactive.
I?ll read up on what I can measure without service accessories like extender board etc.
Tom- Not sure what CLIP is but I see it discussed on a 54111D thread on Yahoo gr oup-thanks,
I?ll have to lurk...9 years of blocked Yahoo password change access by AT&T and 9 years of grief led me to kill all Yahoo-owned accounts and n ow AT&T.
Nobody needs to hear that story.
That scope is heavy and obnoxiously loud. Sounds like it?s awaiting clearance for takeoff, but my basement isn?t long enough for a twi n-propeller scope to
I think I better restrict my posting to a computer. I?m on my phone now and have no idea where my previous drafts are (I hope not posted...apo logies if they are!)
produced, I offered two distractions. The overview described the +300 V su pply as being used for producing the +5 VDC logic supply and the CRT supply as they name it is only +120 VDC. I didn?t mean to sound like only measures 120 instead of 300.
I didn?t (yet) see further explanation of internal functions on the CRT ass?y. I hope it?s an assembly with the ability to pro duce all support voltages for a CRT.
?replace the module?...I get ?why??, durin g the product?s heyday, but that leads to a ?problem? ? period (for wannabe users/restorers) in the future...which is now.
??m just snooping around for answers for that day when all the room lig hts have to be off to see anything. If I?m going to commit space to such a large (and loud!) I?m trying to be proactive.
ke extender board etc.
There's all manner of reasons why it might be dim, including muck on the sc reen. Let us know when you've got some facts we can work with.
Rejuvenation entails *temporarily* running the heater of a tube at a high v oltage, the theory being it boils up the thorium from the cathode and expos es fresh surface. It does not entail leaving the filament at a higher volta ge in operation.
That was done with so-called CRT "brighteners" which were merely step-up au to-transformers. We've all seen those. They worked, for a while. But they d id cause other picture problems, like saturation that made the contrast loo k eerie. Sometimes you could adjust some of that out.
Any tube tester could be used to "rejuv" a tube or CRT. The process was wel l known in the shops. The key was always to leave the tube in the tester fo r some period of time after applying the 2X or 3X heater voltage for a minu te or so (hopefully you didn't burn out the heater) and then seeing if the emissions dropped off unacceptably over the next hour. If emissions stayed up, the rejuv "took" and you were good. If not, maybe you sold a new tube.
The problem with CRT rejuvenation was that the excess electron flow eroded the tiny aperture hole in the gun, causing blurry focus, smear, etc, on the face of the CRT. In lots of cases the customer didn't care, he did not wan t to spring for a new picture tube or new TV.
I often got the job of replacing CRTs after the sets came back in when the rejuvenation didn't hold up, or the customer didn't like the result. I had a knack for doing convergence, which can be one of the most frustrating thi ngs to attempt.
voltage, the theory being it boils up the thorium from the cathode and exp oses fresh surface. It does not entail leaving the filament at a higher vol tage in operation.
auto-transformers. We've all seen those. They worked, for a while. But they did cause other picture problems, like saturation that made the contrast l ook eerie. Sometimes you could adjust some of that out.
ell known in the shops. The key was always to leave the tube in the tester for some period of time after applying the 2X or 3X heater voltage for a mi nute or so (hopefully you didn't burn out the heater) and then seeing if th e emissions dropped off unacceptably over the next hour. If emissions staye d up, the rejuv "took" and you were good. If not, maybe you sold a new tube .
d the tiny aperture hole in the gun, causing blurry focus, smear, etc, on t he face of the CRT. In lots of cases the customer didn't care, he did not w ant to spring for a new picture tube or new TV.
e rejuvenation didn't hold up, or the customer didn't like the result. I ha d a knack for doing convergence, which can be one of the most frustrating t hings to attempt.
The rejuve process used in repair shops that I'm familiar with involves a z apping discharge at the same time as applying heater power. Although it fai rly often restores emission, it's only a short term result, and as the emis sion falls again the tube becomes unusable due to severe smearing.
You could say it was a way to ruin customer TVs prompting another purchase while appearing to be helpful.
The only zapping process I knew of was used when there were shorted element s in the tube. It can't be done with a tube tester -- rather a charged cap. It can restore emissions, depending on what was shorted in the tube. Heate r voltage was not required. If it works, the picture is not typically affec ted. But too often the short cannot be removed. In fact sometimes it welds an intermittent short permanent.
NT: I'm curious as to your understanding of the process you described -- wh at is the mechanism that would be in play that would increase emissions by zapping it while powered? Emissions are largely a function of the cathode q uality (useful remaining life) and unless a zap removes a cathode short, I don't see how it works. Also don't understand how it would contribute to sm ear, or how the emissions would fall again, unless the cathode was already bad, in which case the emissions would not have recovered at all.
Terry
zapping discharge at the same time as applying heater power. Although it f airly often restores emission, it's only a short term result, and as the em ission falls again the tube becomes unusable due to severe smearing.
nts in the tube. It can't be done with a tube tester -- rather a charged ca p. It can restore emissions, depending on what was shorted in the tube. Hea ter voltage was not required. If it works, the picture is not typically aff ected. But too often the short cannot be removed. In fact sometimes it weld s an intermittent short permanent.
what is the mechanism that would be in play that would increase emissions b y zapping it while powered? Emissions are largely a function of the cathode quality (useful remaining life) and unless a zap removes a cathode short, I don't see how it works. Also don't understand how it would contribute to smear, or how the emissions would fall again, unless the cathode was alread y bad, in which case the emissions would not have recovered at all.
Agreed.
I have used charged caps on three occasions (two successful) to restore bad coils in field-coil speakers. I have tried it several times without any su ccess to 'save' open transformer windings.
But, otherwise, 'rejuvenation' for tubes has consisted of over-voltage on t he filament for varying periods of time and at varying percentages over wha t is rated - and not much more. And CRT "Brighteners" increase voltage to t he filament in my experience as well. Some by a variable (adjustable) amoun t as well. Perhaps NT is conflating different processes?
I have a B&K CRT rejuvinator. I pulled the CRT out of my 1948 Andrea. It tested just below the Green range. Hit the zap-o-matic rejuvinator button. It crept up into the Green range. The third time it fell all the way down to the bottom of the Red range.
Well that settles that. Now it's dead instead of very dim.
--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com
The B&K units and their ilk work exactly that way -- increasing the filament voltage temporarily. They may also change the grid bias during the process - not sure.
Jeff, I suspect your filament is open now.... unfortunate.
Ok, a quick google search reveals that the CRT specific rejuvenators apply a high potential between the cathode and G1. The resulting arcing exposes s ome "fresh" cathode surface. I'd have to believe the area would be tiny and therefore the fix very temporary. Seems like it would also be prone to thr owing cathode debris at the phosphor surface, aperture mask, or gun apertur e. Ugh. But now I understand the ZAP reference.
I was familiar with the older method that used general purpose tube testers with CRT adapters. There was no such capability with those that I was awar e of -- only raising the filament voltage to overheat the cathode and boil up the emitting surface. Seems like a better chance of lasting results, if the filament survives the process.
Funny because I owned a B&K 467 for a while, but I don't think I ever tried to use it for rejuvenation.
ments in the tube. It can't be done with a tube tester -- rather a charged cap. It can restore emissions, depending on what was shorted in the tube. H eater voltage was not required. If it works, the picture is not typically a ffected. But too often the short cannot be removed. In fact sometimes it we lds an intermittent short permanent.
- what is the mechanism that would be in play that would increase emissions by zapping it while powered? Emissions are largely a function of the catho de quality (useful remaining life) and unless a zap removes a cathode short , I don't see how it works. Also don't understand how it would contribute t o smear, or how the emissions would fall again, unless the cathode was alre ady bad, in which case the emissions would not have recovered at all.
ad coils in field-coil speakers. I have tried it several times without any success to 'save' open transformer windings.
the filament for varying periods of time and at varying percentages over w hat is rated - and not much more. And CRT "Brighteners" increase voltage to the filament in my experience as well. Some by a variable (adjustable) amo unt as well. Perhaps NT is conflating different processes?
The zapping method was standard in the TV repair industry here while CRTs w ere in use. It only takes a couple of minutes to do.
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talks about a pulse of grid current much improving emission. How it works i s I gather disagreed on, but it does. The problem is the tube declines afte r not long, giving a smeared picture.
y a high potential between the cathode and G1. The resulting arcing exposes some "fresh" cathode surface. I'd have to believe the area would be tiny a nd therefore the fix very temporary. Seems like it would also be prone to t hrowing cathode debris at the phosphor surface, aperture mask, or gun apert ure. Ugh. But now I understand the ZAP reference.
Temporary, yes. Typically the customer would get a few more months service then it became unusable due to smearing as the emission declined.
Throwing crud about didn't matter unless it created a short, which it could .
Some folk think it cleaned a bit of cathode, some thing it created electrod e hotspots that scavenged gas.
I didn't like zapping at all, preferring an extra turn on the loptf heater wind. That gave a much better lasting result and didn't kill tubes.
rs with CRT adapters. There was no such capability with those that I was aw are of -- only raising the filament voltage to overheat the cathode and boi l up the emitting surface. Seems like a better chance of lasting results, i f the filament survives the process.
ed to use it for rejuvenation.
The worst CRT I ever did had no visible emission at all, and the tube type, sony trinitron, was known for not responding to attempts to improve emissi on. I gave it a large permanent heater boost after which it had plenty of e mission all round. But colour tracking was lousy, although it gave a nice w hite the intermediate colours didn't match a healthy set at all well. That thing stayed in service many years and kept going. Occasionally it would ar c over for a moment, causing green output to go way up for a few minutes th en calm down. It was very much an experiment in trying to fix unfixable tub es.
The Trinitrons were among the hardest CRTs to converge. Those square corner s were hell to get right. Some of the Sony chassis had better convergence c ontrols than others. I will say the last CRT Sony I owned, a 35" 220 lb beh emoth, had a beautiful picture and spot-on convergence.
e, sony trinitron, was known for not responding to attempts to improve emis sion. I gave it a large permanent heater boost after which it had plenty of emission all round. But colour tracking was lousy, although it gave a nice white the intermediate colours didn't match a healthy set at all well. Tha t thing stayed in service many years and kept going. Occasionally it would arc over for a moment, causing green output to go way up for a few minutes then calm down. It was very much an experiment in trying to fix unfixable t ubes.
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