This is the first mainframe I got. Of course, it did not work, so I bought it at a good price. It came with a nice bonus; a 7D20 Programmable Digitizer plug-in. Here you have the story of their restoration. It is really a collection of my articles in the firstname.lastname@example.org e-mail List. I have added some pictures to make more interesting the reading and some extra text where needed. Added text is written in italics. Hope you enjoy it!
Well, the saga continues!. Let me explain a bit about my R7603. I got it from a local ham (who is also a microwave engineer and has an outstanding home lab, plenty of spectrum analyzers, generators, counters, ...). He told me he bought this set some time ago, already unworking, but had no time to work on it. So, when he saw my message in a local swap mail list, he sent me a message offering me the set. Well, I went yesterday to his home, at about 115km from mine and picked it up. We were talking for about one and a half hour about, you guess it, test equipment (which is one of my passions!). And about this R7603/7D20 I asked some basic things, as if he had switched it to 220VAC (it is a USA set, so it was originally wired for 115VAC). He told me 'of course!'. But when I arrived home and opened the mainframe, I noticed the main fuse was dead. And it was a 2A fuse, which is the recommended for 115VAC. Furthermore, it was a nice Buss fuse which _could be_ an original part... Hmmmm... So I suspected about the set not being wired for 220VAC, but as I had no manual and it was too late, let it until today.
So this afternoon, having checked all the evident power supply failures (rectifiers, transistors, capacitors, ...), as I didn't find anything wrong, I decided to check the mainframe with a new 2A Buss slow fuse and connecting it to 115VAC (I have a large isolating transformer for this use). So I switched the mainframe (alone, without plugin) and... voilą!. The power light glown and the fan started to rotate!. I had also put my Fluke 77 monitoring the -50VDC line, and it showed a nice reading of -49.9VDC... All the other voltages (+15, -15, +50) where almost exact, so I went for the _real_ test, and put the 7D20 plugin... Powered on... and something was on screen!. Yes, 'FAILURE 521' along some other text. Well, it couldn't be SO easy ;-)!
7D20 failure display
I had never worked with a 7D20 and it took me some minutes to familiarize with its functions. But after a while, I have been able to check most of the functions (both channels, timebase, memories, cursors, trigger, ...) and everything works EXCEPT for these:
*I was unable to center the display vertically with the 7D20 front panel 'display cal' controls; I have resorted to the vertical amplifier 'C' labelled pot to center it (fortunately, my assumption was right and it did the expected effect). Now it is perfectly on place.
*Character generator fails; some characters are shown incorrectly. But not all ocurrences of same char fail. I mean that, for example, a 'E' is shown right in one part of the screen and not so (it is missing points or has points which should not be present) in other display location. So I think the RAM memory which hosts the display map is bad. OTOH, display of the waveforms is fine at any display point, so there should be two layers of display memory, one for the waveforms and another for the characters, which is the one failing.
So I wonder if you could help me with these questions:
(1)Is the 'FAILURE 521' generated by the 7D20 or by the 7603?
(I must admit I was really new to Tektronix 7000 series when I did this question. Analog mainframes, as I learned later, only generate basic text and have no way to give you a failure code)
(2)In both cases, any Service Manual (for the 7603 or the 7D20) around?. I would need only the part regarding that fault, which should be a memory trouble.
(In few days I got a 7603/R7603 and a 7D20 Service Manuals which would probe to be a really nice reading)
And, of course, any advice would be more than welcomed!
All in all, I am happy with the set so far. And hope to be able to get it working 100%
Thanks for your help!
Based on some information I got by e-mail, I checked and the R7603 was wired for 115VAC. Just changing a jumper in the power supply, I got it working at 230VAC R7603 Power Supply detail
Hi my friends,
I did it!. Thanks to Gary N0KQY, who based on the 7D20 technical manual pointed right to the culprit (waveform RAM 1, which is ICU 910, a 4116 16k x 1 static RAM), I have just repaired the 7D20!. Just by replacing it with one found in my 'old ICs' box (hi, I never thought those old chips, taken from old video consoles, would help so much!), now the character display is 100% good and the digitizer passes its self-test.
R7603 Power 7D20 RAM chip detail
7D20 selftest pass!
7D20 before and after
What can I say?. That I am a VERY happy camper tonight!. Yahoooo!!!
I just can't get the smile out of my face ;-). I think this happens to all of us sometimes, am I right?
Best regards and thank you all for your help!
When I talked about my R7603 and its faults I did not tell all the truth... I forgot that the Dark Side had got it and... graticule is always dark ;-)!!!. So, do you have a set of bulbs (3) available for sale?. While checking my 7603/7D20 against my Tek 475 (curious comparison as the 200MHz BW of the 475 has nothing to do with the 'poor' 70MHz repetitive of the 7D20 ;-) ), I noticed how nicer is the lighted graticule of the 475... so I need the bulbs, please!!!
As I did not find replacement bulbs, I managed to repair them. Here you have some pictures about my work to get them lighting again:
R7603 lights on place
As I am still looking for a 7D20 similar to mine (the one with added CH A, CH B, CLOCK and TRIG SMB-type connectors in the front panel) and have not yet found any hint about what that mod was intended for, I have looked in detail to the internal wiring for those connectors... and have found an interesting thing. All of them go directly to the 7D20 back panel coaxial connectors (the ones in the upper part of the plugins; they are in groups of four coax connectors, one for each plug-in position). Looking the front panel of the R7603, starting from the leftmost module, CH A goes to the leftmost coax connector and CH B to the next one (so there are two empty coax positions). Then, in the middle module there is CLOCK, at the leftmost coax connector. And then, in the rightmost module, you have TRIG also in the leftmost coax connector.
7D20 front panel
(Observe the four extra SMB connectors)
So I wonder which signal is present (or you can inject) at those points... It seems as some kind of analog connection, bypassing the digital (7D20) module... Perhaps some kind of markers???. As I have not yet got the 7603 manual, I have no clue of the use of those plugin 'back side' coax connectors... any idea?
7D20 extra coaxial connectors
What seems evident to me is that in an standard 7D20, back side coax connectors are not used, as these four are the only ones used of the 12 available positions; if you take them out, no coax would exit from the 7D20 to the mainframe. Am I right?
Well, this is getting interesting :-)!
Go back to Main Index Page