Audio Precision S1 repair- A common problem is plugging an amp into the output of the AP and frying some components. The initial symptom is incorrect levels below 500 mV. Duke has a test to validate the attenuator accuracy. On this unit it identified the problem an which resistor was most likely bad. Repairing it is pretty involved because you need to access the bottom of the source board. To get there you need to disconnect a lot of stuff and keep track of the connections. Photos help. Someone had tried unsuccessfuly to repair it. In my checking it seemed some relay contacts were cooked. Photos of the parts and damage are below. Next the repair- Fortunately suitable (identical to original) resistors are still available from Mouser. Relays not so available. I found a suitable relay at Mouser, however it draws 4X the current. I have found and ordered some correct relays from China but the one from Mouser arrived much sooner.
After installing the new parts and cleaning everything it still had an issue. Traced it down to a damaged trace from the botched repair. Now it all works to spec.
Attached are before an after repair photos.
After installing the new parts and cleaning everything it still had an issue. Traced it down to a damaged trace from the botched repair. Now it all works to spec.
Attached are before an after repair photos.
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I have spent the last few months repairing Quan-Tech 5173 semiconductor analyzers. It seems no one wants to work on these. The company no longer exists and there are no real modern replacements. And they are essential to meeting some Mil-Spec requirements. They are hard to work on and the docs are not complete and in come cases just incorrect. And the units have been poorly repaired (butchered) in some cases. Here are a few pictures of one.
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Hi Demian,
I'm afraid that butchery is the norm these days. I saw some with really good test equipment in 1999 - 2000, before that with "repair grade" (B&K, Leader) test equipment. In audio, service has scraped new lows. I am having to do down to chassis rebuilds just to get the things back to factory. It's really sad.
I am curious about the AP-1. Doesn't it attenuators on it's inputs? I haven't used one so I don't know. The relay banks would suggest they did. Also, what kind of overload does it take to damage signal relay contacts???? Not unless it is designed for signal line levels only.
I'm afraid that butchery is the norm these days. I saw some with really good test equipment in 1999 - 2000, before that with "repair grade" (B&K, Leader) test equipment. In audio, service has scraped new lows. I am having to do down to chassis rebuilds just to get the things back to factory. It's really sad.
I am curious about the AP-1. Doesn't it attenuators on it's inputs? I haven't used one so I don't know. The relay banks would suggest they did. Also, what kind of overload does it take to damage signal relay contacts???? Not unless it is designed for signal line levels only.
It was the output attenuator that was cooked. Power amp connected to the wrong connections. The AP has its output on the left side. Every other audio analyzer I have used (a lot) has its inputs on the inputs on the left side. Don't think, just plug and poof the magic smoke appears. The source Z is 50 Ohms so many amps could cook it.
I'm not a fan of parts that don't fit. I just yanked and discarded some new Jantzen capacitors someone rammed into a pair of MC60 McIntosh amps. That and a whole bunch of "audiophile approved" parts. Now everything fits, it's neat and will actually last. They even replaced wire for Teflon type. I replaced it, ran it properly so the amps are also stable.
I have measured and listened to all kinds of capacitors. Audiophile type caps are no better than good industrial capacitors (that are smaller), and very often are not as good. I don't know why you have 800V caps in that location either.
Anyway, whatever.
I have measured and listened to all kinds of capacitors. Audiophile type caps are no better than good industrial capacitors (that are smaller), and very often are not as good. I don't know why you have 800V caps in that location either.
Anyway, whatever.
I always explain reality, then if they insist I will either pass on the job, or do it. I would never have installed those capacitors in that unit. I'd rather walk on the job (and I have). #1 rule, the parts must fit. If they don't, I won't install them. There is enough work out there that I don't have to perform jobs that aren't right.
It is likely you had to enlarge the component holes for the leads on those caps. Big no-no.
It is likely you had to enlarge the component holes for the leads on those caps. Big no-no.
"To each his own" but replacing 10 uF caps with 2 uF caps on long leads will both reduce the low frequency extension and add inductance, along with the inductance intrinsic to a large axial component. I would have recmended bypassing the 10 uF cap with a .1 uF film or NPO ceramic. No brand cachet but better electrical performance.
Just started on a nice little HP 209A. Other than a general cleaning, the main gears were very gummed up and hard to turn but that was fixed easy enough. As expected, the caps on the PS board are all pretty much toast - included what was needed on the current Mouser order. No major drama or war stories with it - just a nice addition to my collection; I didn't have one of these and had been looking for one so I'm quite happy with how it seems to be turning out.
Hal
Hal
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Yes, I do have strong opinions. Sorry. It's great you didn't have to enlarge the holes.
I was trained by old techs (apprenticed), uni, then by several large audio manufacturers. For most of my career I maintained equipment under warranty contracts. There are in fact right and wrong things to do to equipment. I have always had to rescue equipment from the effects of "improvements". So that is where my strong opinions come from. Experience in test and measurement / calibration also affects how I practice and think. I always measure before and after performance (most people don't), and listen to the thing.
You can obviously improve equipment performance with modern components in the right places, or modern circuit techniques. But you have to make certain those changes actually do effect improvements. You cannot do that without equipment able to measure to the levels (or beyond) you are working at.
That's the simple truth. I am not trying to push you at all. You should pay attention to Demian's comments as well.
I was trained by old techs (apprenticed), uni, then by several large audio manufacturers. For most of my career I maintained equipment under warranty contracts. There are in fact right and wrong things to do to equipment. I have always had to rescue equipment from the effects of "improvements". So that is where my strong opinions come from. Experience in test and measurement / calibration also affects how I practice and think. I always measure before and after performance (most people don't), and listen to the thing.
You can obviously improve equipment performance with modern components in the right places, or modern circuit techniques. But you have to make certain those changes actually do effect improvements. You cannot do that without equipment able to measure to the levels (or beyond) you are working at.
That's the simple truth. I am not trying to push you at all. You should pay attention to Demian's comments as well.
For me, electronics is an escape from some really ugly stuff that I can't do anything about. I get great ideas from many here, but just put in a more diplomatic way. That is the key between appreciation and a fist fight with me. At the moment, I am extra sensitive about life for what is happening around me right now, and I am aware of it. I'm noy going talk about who I was and the greatness of those who trained me. I could not live up to who they were. This is going a little sideways because of my reaction to how I saw things that were presented to me here.
My best bet considering where I am at right now is to bow out. I do appreciate the cap bypass by the way.
My best bet considering where I am at right now is to bow out. I do appreciate the cap bypass by the way.
Thanks! They are nice little oscillators. That is one model that I've been keeping an eye out for a while but up until this one they have all been in poor condition or overpriced. A ton of them were made but it seems unusual that I just don't see that many of them for sale... maybe people just hang on to them since they are simple, small and just work.
I for one hate to see someone go over something like this. There are a lot of very opinionated people on the various forums here and very few of them are shy about making those opinions known. IMHO most of them have opinions formed from drinking the Kool-Aid of whomever is spouting off in favor of whatever opinions that they already have. Others have opinions formed on knowledge gained from a lot time spent in the trenches working and learning about the equipment and gear that they love - seeing what works and what doesn't and are willing to learn from their experiences both good and bad. In this particular instance you were communicating with one of the latter. Did they sugar coat their words or be overly tactful? No, but I've noticed that those into technology or engineering tend to be that way - and while one can learn an extremely large amount joining in "discussions" with them, a thick skin is pretty much a requirement to partake. And if things get to the point that you truly take offense or are bothered by what someone says, try in a polite and tactful manner to let them know. Yes, there are way too many trolls around but I think that most of those whose knowledge and opinions really matter will back off, apologize if necessary, and resume in a calmer manner.
But, then again, I'm one of those with strong opinions so take all of the above as you will.
Hal