Hello Calvin,
I see. Sorry about the mix up. Just want to make sure. The basic tests are [Shift + Free run], [Shift + Manual] (done), and [Shift + M4].
[Shift + Free run]?is for the lighting and is to make sure all LEDs light up like Christmas. It also indirectly tests the processing side by noting that the correct behavior of the marching pattern as described in the manual. You've pressed [Shift + Manual]?for the fault annuciator already so we know to focus on the ADC. As for [Shift + M4], I don't think it'll be of any help but you can try. Actually I forget what it will do with an ADC fault. Its a diagnostic test that tests everything and will list everything. The thing to note here is that an ADC is higher in the chain vs individual components tethered to sections of the rf path. The Processing section being the highest in the chain.
You're right that 8340B schematic is literally broken and 8340A (assuming this since they don't have a 8341A) is unreadable but did you try all of the manuals? 8340A 8341A 8340B and 8341B are all the same except for FM input, SYTM for 20GHz vs 26.5GHz, and a sweep output 5 vs 10 V/GHz. I do admit it is still hard to read but I've seen harder. 8673B + 8673C/D service manuals were insane before I found a recent independent scan via google search and this group. Here is a link for 8341B component level volume. (page 201)
?
Be sure to read up on theory of operation for A27 in the assembly level volume as well. A21 is involved based on the RF block diagram. What its doing and how it affects A27 that would have to be read. I see "ADC timing"
as the name of the signal between those boards.
If worse comes to worse there is google and bitsavers for individual component catalog/product guide searches (ie. motorola, nec, pmi, national semiconductor).??or ebay at the assembly level.
So far it looks good in terms of economical repair. Anything encased in a solid block of metal that is damaged on the RF path is expensive. Can still be repairable within economical means as shown by Tobias' recent post. That was really lucky though imo. If the damage was on a hybrid circuit (ie bond wire or MMIC amp, transistor, diode)..... uneconomically repairable. It can still be repaired but you'd need to be in the business of wire bonding and Microwave IC design or negotiate the replacement assembly's the price down. Prices can be negotiated down if you know if the component is used in another instrument. HP usually repurposes the same components in different equipment. An example is a hybrid circuit I thought I was doomed to be unobtainium. Turns out this circuit is used in 3 instruments. What would have been a $600 - $1500 part was negotiated down to $175. Probably lower with the way things are trending. Checking now, there is a seller selling more than 10 but doesn't know what they have. There is another seller also selling extra components along with the component of interest for half of what the lone assembly would go for. Anyways I don't believe you will have this problem or those types of hoops and hurdles. I suspect a few components on a board assembly or 2 is the issue that failed due to old age. ICs or capacitors that age with heat, cycle use, and naturally occurring chemistry (oxides and acids forming). Compare that to someone that put in too strong of a signal and blew the inputs of the AM and PM. Worse would be the RF output (that attenuator and other RF modules are not cheap) or a physical drop of the instrument or on top of the instrument due to moving. Good luck with your potential buy.
-Lex
