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Re: Advice on Buying a 7904A
John Griessen
On 12/9/21 14:45, Dave Daniel wrote:
I always capture the eBay listing and whatever photos are on the listing and save them away just in case they turn out to be useful to document damage that occurs during packing or shipping.Yes, if anything is not in photos yet, and it is ebay, try to get seller to do photos. Then they will assist you in negotiating damage down down in dollars. |
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Re: Help required finding a Tek 466 power rail short
Ok, good so far.
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You may want to see if Artek Media has a manual with the appropriate serial number. I'd disconnect everything from the supply, and then check the +5 and +15 volt rails again for shorts.? Then if you have an ESR capacitor checker, check the output capacitors.? Also check the bridge rectifier because a shorted diode in any bridge generally results in a pretty much dead short across the transformer secondary.? In fact, I'd be tempted to check the bridge rectifiers first, then the capacitors. If the 15 volt line (for instance) reads a dead short, then check on the other side of the pass transistor.? I would not expect that reading to be a dead short.? If, on the other hand, the transformer secondary reads a dead short with the probes in both directions, then a shorted diode.? (This depends on the rectifier configuration).? I'd be checking them and not waste fuses. Most important thing is to have the power supply disconnected from the rest of the scope. I generally like to make a copy of the schematic and then note the readings I make.? That can often give a good idea for an overall view of the problem. Harvey On 12/9/2021 4:35 PM, James55 wrote:
Thank you Harvey for the helpful advice. |
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Re: Need a 465 Slope Level potentiometer/ switch
Second that.
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I found the power light for my 453 there that I'd been looking for for quite some time and it was very reasonably priced. Thanks, Barry - N4BUQ ----- Original Message -----
From: "Ananda via groups.io" <adesilva_1999@...> Here is another source for TEK parts: |
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Re: Model 3 cart
I could use another. Where are you located??
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DaveD On 12/9/2021 4:40 PM, Carl Hallberg via groups.io wrote:
Anybody need a cart?? Pickup only. --
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Re: Advice on Buying a 7904A
Of the four 7xxx 'scopes that I have purchased through eBay, all were packed ridiculously poorly and all survived the trip without damage. I think the highest price I paid for any of those was around $150.
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The main danger is that the front panel controls could be damaged if the front of the 'scope is not protected from hitting the inside of the box. I would strongly suggest that if you do buy the 'scope, ask the shipper to pack the plug-ins separately with lots of bubble wrap around each, particularly the front panels. It sounds, though, that the seller is not very responsive. That would leave only the 'scope's controls in danger. I always capture the eBay listing and whatever photos are on the listing and save them away just in case they turn out to be useful to document damage that occurs during packing or shipping. DaveD On 12/9/2021 4:00 PM, cmjones01 wrote:
On Thu, 9 Dec 2021, 20:12 John Griessen, <john@...> wrote:On 12/9/21 10:22, Jeff Dutky wrote:They can be surprisingly tough. I bought my 7904A mainframe from eBay inThey sent me some pictures of the unit from other angles, and the restof the case looks to be in good condition, with no obvious dents or --
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Re: Help required finding a Tek 466 power rail short
Thank you Harvey for the helpful advice.
As I mentioned, none of the rails are correct as the fuse blows if it is connected to the mains. Currently the 5v and 15v rails give a direct short with an ohm meter. The serial number is lower than the 200000 which is were the manual was updated. Anyway, have the 50 ohm resistor and shall have another look... |
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Re: Advice on Buying a 7904A
On Thu, 9 Dec 2021, 20:12 John Griessen, <john@...> wrote:
They can be surprisingly tough. I bought my 7904A mainframe from eBay in the US for an absurdly low price because it had no plugins. It came via the eBay shipping program and arrived here in Poland in an enormous cardboard box full of polystyrene chips. That was the only packing. It Just Worked and met spec. To this day it occasionally emits the odd polystyrene chip, though. Chris |
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Re: Advice on Buying a 7904A
John Griessen
On 12/9/21 10:22, Jeff Dutky wrote:
They sent me some pictures of the unit from other angles, and the rest of the case looks to be in good condition, with no obvious dents or scratches, and no significant discoloration. The damage to the vertical plug-ins is consistent with damage I have seen on other 7A26s and 7A18s, so I'm not too concerned about that.Does it have to be shipped? That can be the end of a 7904 if not packed well. |
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Re: Advice on Buying a 7904A
One downside of the 7904 as compared to the 7904A is that the 7904 does not have the kick-stand feature, where the top (display) half of the 'scope can be lifted up and placed on a kickstand for working on the instrument. I've worked on both, and the 7xxx 'scopes with the kick stand are definitely easier to repair.
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DaveD On 12/9/2021 12:35 PM, Jeff Dutky wrote:
Roger, --
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Re: Advice on Buying a 7904A
Roger,
Yes, I think that the beat up righthand plug-in is a 7A24. The single slider switch and the labels above the BNC connectors are a dead giveaway. I am pushed for space as well, but I'd really like to have a four-slot mainframe with more bandwidth than the scopes I currently have (my fastest scope is currently a 2465 at 300 MHz). I would prefer a 7904, both because of the more elaborate front panel controls, and because it doesn't use HYPCON hybrids, but this price is pretty good. -- Jeff Dutky |
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Re: Advice on Buying a 7904A
Chris,
Thanks for the response. Yes, the plug-ins are a bit banged up. I'm not sure that both A and B are selected; I thought that only B was selected, which would also be invalid since there's no plug-in in the B horizontal slot. I said that the seller was playing dumb, but maybe it's not an act. They sent me some pictures of the unit from other angles, and the rest of the case looks to be in good condition, with no obvious dents or scratches, and no significant discoloration. The damage to the vertical plug-ins is consistent with damage I have seen on other 7A26s and 7A18s, so I'm not too concerned about that. The CRT seems to be the least replaceable part of scope (though I understand it also uses a bunch of custom ICs and hybrids), so I just wanted to be sure it was not obviously damaged. -- Jeff Dutky |
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Re: Advice on Buying a 7904A
OK, just tried this and I can get a similar result. Both A and B timebase
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buttons pressed, intensity cranked up, I get a fair glow on the whole screen, with normal readout (though more flickery than usual). So a known good 7904A can behave like this. That doesn't mean the one you're looking at is all good, of course, but the photo doesn't definitely mean it's broken. Looks like it's been bashed around, though, with broken knobs and plugin tabs. Chris On Thu, 9 Dec 2021, 17:53 Chris Jones, <chris@...> wrote:
Looks like both A and B timebase buttons are pushed in, which is an |
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Re: Advice on Buying a 7904A
Looks like both A and B timebase buttons are pushed in, which is an invalid
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combination, and the intensity is cranked up to maximum so the screen illumination is probably just a very intense spot somewhere off the side of the screen. I'll try the same settings on my 7904A and see if it behaves the same. Chris On Thu, 9 Dec 2021, 17:44 Jeff Dutky, <jeff.dutky@...> wrote:
I'm thinking of buying a 7904A that I found on-line for a relatively low |
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Advice on Buying a 7904A
I'm thinking of buying a 7904A that I found on-line for a relatively low price ($90), but there's very little info and the seller is playing dumb.
I've uploaded a picture of the instrument to this album: /g/TekScopes/album?id=270678 It looks like a number of the pushbutton lamps are burned out, but I my real concern is the even illumination of the CRT (and no readout). Does this indicate a specific failure mode for the CRT, or is this just the seller setting the INTENSITY controls stupidly? -- Jeff Dutky |
Jared Cabot
James55
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