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).
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,
On "my" schematic 34 there is no U1620A or U2 and no D181 or U3.
I found the TL 72 OpAmp.
I have a U900 aa vertical D/A converter an a U1010 as horizontal D/A converter.
Gerhard
--- In TekScopes@..., David <davidwhess@...> wrote:
I assume that the character display works correctly even when the
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.
Gerhard
--- In TekScopes@..., "g_kupka" <ghm1@> wrote:
I swapped the RAM Board and now the 2nd 7854 has the opt 2D.
The 1st 7854 has still the problem, that it doesn't display the stored signal in the store mode, it shows only a horizontal line.
Where can I find the failure?
Many thanks.
Gerhard
--- In TekScopes@..., "David C. Partridge" <david.partridge@> wrote:
Yes
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
David Hess