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Tek 7904 Display Problem
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Don Crano
Hi All
My old faithful 7904 has started to have a little problem with the display. It will run for hours or days with no problem. Then it will start to drift the display up and down, this is the trace/s and readouts as well. Note this is not on oscillation up and down. It will shift up for awhile, then drop down lower then it should be for awhile. I am talking about a 1/2 CM or so. Everything is always on screen, it just gets annoying after awhile. I found I can turn off the readouts and it will stop. Turn the readouts back on, and it will be fine again for a few hours or days. Any ideas what might be going on and where to start looking before I tear into it. Thanks, Don BTW Hi Mark Gurries glad to see you on the list. |
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Mark Gurries
BTW Hi Mark Gurries glad to see you on the list.Hi Don. Been watching the list for a while. It was from one of your email on the DCC list that I learned about this list. Anyway... I told Jim Williams here at Linear Tech about this list. (My Lab bench is next to his.) But he is not one to use PC's. That Jim for ya. For those who are not familiar with Jim, he is one of out treasured assets at the company. Hi writes many application notes for our IC and tackling problems and parts that cause most of us to glaze over our eyes in terms of the accuracy or noise level requirements. Things like how do you verify all 24 bits of a 24 bit DAC! The trick around here to getting a Tek scope fixed and checked out by Jim Williams is to get an old 500 or 400 series scope in the lab. Tell Jim about it, and the fact that it does not work annoys Jim to no end. Before you know it, he is digging into the scope and fixing everything. Not that we cannot fix out own scopes mind you, but, Jim does a faster and better job than anyone I know. It fun to watch him and of course you learn along the way the history and debug tricks. We have about every make of Tek scope at the company labs. We have lots of 547's working in parallel with the latest Tek Scopes. We just got around to setting up an old 556 dual beam on another engineers lab bench. 454's are another favorite. A few of the guys have 7K stuff like yours. One of my employees has every 7K plug in made including some test adapters if I recall correctly. It amazing to see the latest scopes setup right next to an old classic. The biggest reason we like the old 400 and 500 series scopes is the very fine trace and excellent noise floor. When Jim sets up his 556 with two 1A4 plugins showing 8 traces that are all beautifully detailed (4 of the traces are on a different time base to boot) published in a App note, we sometimes get letters and calls about the scope photo alone! How did you do that? We think that our lab is one of the biggest consumers of electricity in Silicon Valley with all these Tube Tek scopes on and possibly the source of all the blackouts here in California. We already went though one air conditioner! ;-0 Best Regards, Mark Gurries gurriesm@... --------------------------------------------------------- Promotor of the DCC Standard for Model trains. Model Railroad Club and NMRA DCC presentations are at: -------------------------------------------------------- Audio Enthusiast (Love SAE equipment) ---------------------------------------------------------- |
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Don Crano
Hi Mark,
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Yeah I remember posting a list of the YaHoo groups I belong to. I know what you mean about the older scopes and their fine trace lines. My old 453 is still on of my favorites, I can sync it on anything I feed into it.<g> Under it sits a 475A with it's mixed mode delay is nice, but does not have the fine trace of the ol 453. On a Tekmobile 3 I have the 7904, with the two lower shelfs each holding a TM504A, and both fully loaded with plug-ins. So it is my mobile work bench, I can take it any where around the layout as need be.<g> I really do not have a count of the 7K and TM plug-ins I have and what works and does not work. But I am sure I do not have them all. Then on my bench I have a 2230 for what ever analog/digital I might need. Don Remember Always Have Fun and Enjoy!, Don Crano Akron, Oh NMRA #096211 mailto:donc@... Visit Model Railroading with DCC at: Join Model Railroading with DCC Web Ring. ----- Original Message -----
From: Mark Gurries <gurriesm@...> To: <TekScopes@...> Sent: Thursday, April 19, 2001 6:12 PM Subject: Re: [TekScopes] Tek 7904 Display Problem BTW Hi Mark Gurries glad to see you on the list.Hi Don. Been watching the list for a while. It was from one of your email on the DCC list that I learned about this list. Anyway... I told Jim Williams here at Linear Tech about this list. (My Lab bench is next to his.) But he is not one to use PC's. That Jim for ya. For those who are not familiar with Jim, he is one of out treasured assets at the company. Hi writes many application notes for our IC and tackling problems and parts that cause most of us to glaze over our eyes in terms of the accuracy or noise level requirements. Things like how do you verify all 24 bits of a 24 bit DAC! The trick around here to getting a Tek scope fixed and checked out by Jim Williams is to get an old 500 or 400 series scope in the lab. Tell Jim about it, and the fact that it does not work annoys Jim to no end. Before you know it, he is digging into the scope and fixing everything. Not that we cannot fix out own scopes mind you, but, Jim does a faster and better job than anyone I know. It fun to watch him and of course you learn along the way the history and debug tricks. We have about every make of Tek scope at the company labs. We have lots of 547's working in parallel with the latest Tek Scopes. We just got around to setting up an old 556 dual beam on another engineers lab bench. 454's are another favorite. A few of the guys have 7K stuff like yours. One of my employees has every 7K plug in made including some test adapters if I recall correctly. It amazing to see the latest scopes setup right next to an old classic. The biggest reason we like the old 400 and 500 series scopes is the very fine trace and excellent noise floor. When Jim sets up his 556 with two 1A4 plugins showing 8 traces that are all beautifully detailed (4 of the traces are on a different time base to boot) published in a App note, we sometimes get letters and calls about the scope photo alone! How did you do that? We think that our lab is one of the biggest consumers of electricity in Silicon Valley with all these Tube Tek scopes on and possibly the source of all the blackouts here in California. We already went though one air conditioner! ;-0 Best Regards, Mark Gurries gurriesm@... --------------------------------------------------------- Promotor of the DCC Standard for Model trains. Model Railroad Club and NMRA DCC presentations are at: -------------------------------------------------------- Audio Enthusiast (Love SAE equipment) ---------------------------------------------------------- To unsubscribe from this group, send an email to: TekScopes-unsubscribe@... Your use of Yahoo! Groups is subject to |
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--- In TekScopes@y..., "Don Crano" <donc@s...> wrote:
Hi Alldisplay. to drift the display up and down, this is the trace/s and readouts as well.Note this is not on oscillation up and down. It will shift up for awhile,then drop down lower then it should be for awhile. I am talking about a 1/2CM or so. Everything is always on screen, it just gets annoying after awhile.readouts back on, and it will be fine again for a few hours or days.Hello Don, I had this problem. It turned out to be the channel switch hybrid U625 (part nr. 1555-0060). This is located on a 'mezzanine' PCB behind the two vertical plugins. Some other sources mentioned the two 1W metal film resistors on the vertical amplifier. hope this helps Patrick |
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