How to upgrade a 7854 to opt 2D
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Yes
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Dave -----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of g_kupka Sent: 17 March 2013 10:22 To: TekScopes@... Subject: [TekScopes] How to upgrade a 7854 to opt 2D I have two 7854. 1st one opt 2D(extended memory): I can store a signal, but it doesn't show the stored signal in the store mode, it shows only a horizontal line. 2nd one opt 78(P11 CRT): It works well. Can I upgrade this mainframe to opt 2D by swapping the memory board from the 1st one to the 2nd one? Gerhard ------------------------------------ Yahoo! Groups Links |
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I assume that the character display works correctly even when the
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stored signal has no or a low vertical deflection. I think you will find the problem around U1620A or U2 on schematic 34. If reseating those ICs or the A40 connections does not resolve the problem, then you could swap U2 with a different DG181 like U3 to see if the problem moves to the horizontal axis. I have read about reliability problems with the DG181 before. The TL072 used for U1620 has lots of possible replacements including the TL082 and any number of other FET and MOSFET input operational amplifiers. There could be a bad part in the networks surrounding U1620A. On Mon, 18 Mar 2013 16:44:53 -0000, "g_kupka" <ghm1@...> wrote:
After a warmup time of approx 2 hours the stored signal is displayed in the stored mode but only with an ampltude of 35% of the applied signal. |
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There are two versions of board A29 divided at 7854 serial number
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B085124 and below but the schematics are basically identical. DG181 is the part number used for a bunch of the analog multiplexors. The newer version replaced the LF13333 multiplexor (U1720) with a pair of DG181 multiplexors (U2 and U3). Accounting for the minor part number differences: I think you will find the problem around U1620A or *U1720* on schematic 34. I have read about reliability problems with the *LF13333* before. There are old posts in the message archive about possible substitutions for it. The TL072 used for U1620 has lots of possible replacements including the TL082 and any number of other FET and MOSFET input operational amplifiers. There could be a bad part in the networks surrounding U1620A. On Mon, 18 Mar 2013 19:51:21 -0000, "g_kupka" <ghm1@...> wrote:
Hi David, |
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But stick with a real LF13333N if you can. The alternative isn't as good for this application (I don't think it turns on as rapidly).
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Dave -----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of David Sent: 18 March 2013 20:47 To: TekScopes@... Subject: Re: [TekScopes] Re: How to upgrade a 7854 to opt 2D There are two versions of board A29 divided at 7854 serial number B085124 and below but the schematics are basically identical. DG181 is the part number used for a bunch of the analog multiplexors. The newer version replaced the LF13333 multiplexor (U1720) with a pair of DG181 multiplexors (U2 and U3). Accounting for the minor part number differences: I think you will find the problem around U1620A or *U1720* on schematic 34. I have read about reliability problems with the *LF13333* before. There are old posts in the message archive about possible substitutions for it. The TL072 used for U1620 has lots of possible replacements including the TL082 and any number of other FET and MOSFET input operational amplifiers. There could be a bad part in the networks surrounding U1620A. On Mon, 18 Mar 2013 19:51:21 -0000, "g_kupka" <ghm1@...> wrote: Hi David, ------------------------------------ Yahoo! Groups Links |
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I remember the thread where this was discussed. If an SW06 was used
to replace the LF13333, then I think the timing problem could be fixed by altering capacitors C2310, C2400, and C2300 a little bit to adjust the delays but since the SW06 analog switch is even less available than the LF13333, the easiest solution would be to just buy a couple of the original part. I just did a search and found only the SW06 as a viable direct replacement because all of the other quad analog switch candidates lack the disable pin. Comparing the old and new design 7854 designs, it looks like Tektronix had the same problem (Maybe they found the LF13333 switches to be unreliable?) so they designed the A40 board with a bit of extra logic, one quad 2-input NAND gate, to add the enable function to a pair of standard DG181 analog switches. They mounted the small A40 board directly to the back of the A29 board. On Mon, 18 Mar 2013 22:39:52 -0000, "David C. Partridge" <david.partridge@...> wrote: But stick with a real LF13333N if you can. The alternative isn't as good for this application (I don't think it turns on as rapidly). |
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FWIW you can order Analog Devices SW06GPZ online direct from Analog Devices online throught their sample program ...
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Regards, David Partridge -----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of David Sent: 19 March 2013 00:36 To: TekScopes@... Subject: Re: [TekScopes] Re: How to upgrade a 7854 to opt 2D I remember the thread where this was discussed. If an SW06 was used to replace the LF13333, then I think the timing problem could be fixed by altering capacitors C2310, C2400, and C2300 a little bit to adjust the delays but since the SW06 analog switch is even less available than the LF13333, the easiest solution would be to just buy a couple of the original part. |
David C. Partridge
David Hess