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Old 07-16-2011, 02:29 PM
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Simpson 2701

Here are some pictures of the inside of my 2701. It powers up, but only the kOhms range is close to working properly. DC volts has a variable offset (usually reads around .5v with the leads shorted). AC volts fluctuates all over the place, even with the leads shorted.

So far, I've checked all the basics, cleaned switches, controls, and connectors. I've spot checked at least one of each type of cap, and they were all perfect. The power supply seems to be working properly as far as I can tell with the vague information in the service manual.

This is what Simpson sent me a few years ago:
http://wine-in-a-box.org/AK/2701%20Service%20Manual.pdf

The only adjustment I've been able to ID is the one for the -61/-60 volt regulator. It was wayyyy off, but within range of the adjustment. Either someone has been tweaking things, or something else is wrong. None of the boards are silk screened, which makes matching the block diagram to the boards difficult.

It's very compact for what it is. It's spotlessly clean, so considering that it has a fan, it probably wasn't used much.
Attached Images
File Type: jpg 2701-1.jpg (116.6 KB, 35 views)
File Type: jpg 2701-2.jpg (128.0 KB, 21 views)
File Type: jpg 2701-3.jpg (77.5 KB, 26 views)
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Old 07-16-2011, 03:35 PM
bob91343 bob91343 is offline
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Perhaps a leaky transistor. When was this built, and what are some of the transistor types?
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Old 07-16-2011, 05:55 PM
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It's from the late 60's. The transistors are all European types, mostly made by ITT, and SGS. A few random types are DW6467, DW6501, and BCY59VII. There are a lot of transistors, so I can't really test them all. Either way, I'll need to know what the adjustments to to calibrate it.
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Old 07-16-2011, 06:20 PM
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Let's try this again....

It's a rebadged Metrawatt:

Here's the complete manual:

http://www.rainers-elektronikpage.de/DIGITAVO.pdf


The cheesehead screws helped me close in on it. I have a Metrawatt Freq. Counter, Nixie type, all germanium inside, and good to a whopping 500Khz.

sprechen sie deutsch?? I might have a resource - a retired Navy Electronics Tech, born in Germany and fluent in electronics and German.

Cheers,
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Old 07-16-2011, 07:40 PM
bob91343 bob91343 is offline
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I kinda figured Simpson engineers weren't capable of designing such a beast, so different from their usual products.

I have an old HP counter that looks very much like that inside. But it works great, the 5245L I think. Silicon transistors.
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Old 07-17-2011, 01:24 AM
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Brian, that's it! Thanks for figuring out who made it. Still not full schematic, but it identifies all the adjustments. It looks like that manual will fill in most of the gaps in the Simpson service manual. Now I just need to OCR and translate it. Even with no German, a lot of it is pretty obvious.
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Old 07-17-2011, 10:48 AM
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I managed to translate enough of it to at least identify all of the adjustments, and get a little more understanding of how it works. I could still use the calibration procedure, and a full schematic with all the component values.
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Old 07-17-2011, 09:08 PM
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I've made a little progress on the DC offset, but it's not perfect. The AC volts is still completely unresponsive. It either reads out of range, or a wildly fluctuating voltage. I'm not sure if it's related to the other problems, or which board is the problem. Only having a block diagram is like navigating around LA with only a map of the freeways. I think I'm going to have to shelve this project until I either find a parts unit, or some better documentation.
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Old 07-17-2011, 09:27 PM
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Quote:
Originally Posted by andy View Post
Only having a block diagram is like navigating around LA with only a map of the freeways.
I thought the 405 was closed.....

PS - My German buddy at church is VERY interested in translating the manual, or at least the sections germane to calibration, and AC, obviously. I'll print it out and leave it for him - maybe he can get to it quickly. He's 70ish, and retired, but active with the food pantry, Boy Scouts, and other duties.

Cheers,
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Old 07-18-2011, 12:50 PM
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Correct me if I'm wrong, but I don't think there's a section about calibration to translate. I suspect there's a separate calibration manual that I need, and who knows if they ever released it, or the schematic to the public.

I was able to use OCR, and Google translate to figure that it covers the operating instructions, general theory of operation, circuit description, and how to check that it's working properly. It tells you what all the controls do, and how they relate to the circuit, but not how to adjust them (which is far more than I had before, so thanks anyway). If it was working, I could probably touch up the calibration now.

For example, knowing that R5 is the comparator amp null is helpful, but it doesn't tell me which test point to null, or what the conditions of the adjustment are.
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Old 05-30-2012, 11:07 AM
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I'm finally getting back to this after almost a year of sitting on a shelf.

To refresh, it has been having trouble with unstable and wildly inaccurate readings in all ranges. This week, I tried injecting a voltage after the amplifier stage (more or less directly into the A to D). This resulted in a stable, reproducible reading, so at least I know the A/D and and the digital circuits are working.

This made me focus on the main amplifier (a complex module with 3 boards sandwiched together). I checked all the caps, and did an in circuit test of the transistors and diodes. I ended up finding an open diode and I'm trying to figure out if it's anything special. It is labeled

"NT 9757 N".

There is one other identical diode on the board that measures like a normal silicon diode, but it looks like it could be something special. It's a very large diode considering that it doesn't appear to be in a circuit that would see much current, or high voltage.

For now, I've replaced it with an ordinary high speed silicon diode. Things are working better, but it still has accuracy problems on low ohms and DC volts (maybe a calibration issue), and AC volts/amps show over range even with no input. k ohms, and M ohms are right on, and DC current and DC mV are also good. It's about 4% low on DC volts, and about 10% low on ohms. Some, or all of that might be calibration, so I won't worry about it until I get AC volts working and hopefully learn more about the mystery diode.
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