Yeah, I'm in that one. If I remember correctly, it took over a week to get 'approved'. So hang in there, the mod evidently has a lot of other stuff going on.
Sorry, I know zip about your scope model. Do you have a service manual? If no, there are some manuals for it at the "boat anchor manual archive" www.bama.sbc.edu/ , doesn't say whether they are owners' or 'service' though.
Sorry, I know zip about your scope model. Do you have a service manual? If no, there are some manuals for it at the "boat anchor manual archive" www.bama.sbc.edu/ , doesn't say whether they are owners' or 'service' though.
The mod might be out of town or something. Just give it time.
"planning to recap the power supply" IMHO, general replacement of parts not proven to be defective is usually a bad idea in quality test equipment. Get a bridge and check the caps. If the values and dissipation factors are reasonable, leave 'em alone. The odds of creating problems where none exist is far greater than of improving anything. I refer to the problem as "technician blight", having purchased many things that would have been better off left alone. OTOH, if I find a particular brand and style of part where more than a couple are going bad, I do replace all of that particular type that may be present.
"planning to recap the power supply" IMHO, general replacement of parts not proven to be defective is usually a bad idea in quality test equipment. Get a bridge and check the caps. If the values and dissipation factors are reasonable, leave 'em alone. The odds of creating problems where none exist is far greater than of improving anything. I refer to the problem as "technician blight", having purchased many things that would have been better off left alone. OTOH, if I find a particular brand and style of part where more than a couple are going bad, I do replace all of that particular type that may be present.
I understand what you're saying, but this piece is from the early 80s and it needs it. Several caps have leaked, one already replaced. I'm only doing the aluminum electros not the tantalums which there are a lot of. There are not that many electros and most are in the power supply.
I agree, I seriously dislike working on equipment that has been previously screwed up.
Pete B.
I agree, I seriously dislike working on equipment that has been previously screwed up.
Pete B.
Tantalums don't generally have age problems so maybe I'm just unlucky, but check those as well. I've seen them go bad (ok, in HP stuff, not Tek) and it seems that either type of cap is much more prone to failure if the value is high and the voltage is low, say 500uF/6V. I have a Tek 7834 and a full compliment of plug-ins that works well, though I usually only pull it out when I need speed or storage. Believe it or not, a 545B fulfills all my space heating and daily troubleshooting needs 
bwaslo said:
Yes, got these manuals:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWNX:IT&item=220332800087
Fixed a few mechanical issues in the power supply, then powered it up carefully. Pre-regulator outputs were fine, but the +15V and +5 V reg were 0 Volts. Measured voltage on the current sense resistor for the +15V and it was limiting at 3.33A. +15V measured .3 ohms to ground - essentially shorted. Narrowed this down to a shorted big blue tantalum 100 uF 25V on the main interface board. People on the TekScopes group confirm that this is a fairly common failure. The 5V reg uses the +15V in the driver stage and that is why this output was 0V.
Most tantalum caps are not designed for power supply decoupling. Many have peak ripple current specs of about .5A, and we see above that the 7704A will supply 3.33A max during each power up cycle. Tantalums unfortunately fail shorted which can cause burnt traces and smoke in systems that do not have current limited power supplies. There are newer tantalums designed for power supply decoupling, some have max ripple currents of over an Amp, others have internal fuses so that if the cap section shorts the fuse blows rather than traces on the board.
This blue tantalum has no markings indicating the brand and I wonder if it is a low quality part.
The scope is working fairly well at this point.
Pete B.
Most tantalum caps are not designed for power supply decoupling. Many have peak ripple current specs of about .5A, and we see above that the 7704A will supply 3.33A max during each power up cycle. Tantalums unfortunately fail shorted which can cause burnt traces and smoke in systems that do not have current limited power supplies. There are newer tantalums designed for power supply decoupling, some have max ripple currents of over an Amp, others have internal fuses so that if the cap section shorts the fuse blows rather than traces on the board.
This blue tantalum has no markings indicating the brand and I wonder if it is a low quality part.
The scope is working fairly well at this point.
Pete B.
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