EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: maxwell3e10 on May 18, 2022, 06:30:46 am
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I am trying to replace a burned-out HP analog panel meter part number 1120-1147. It seems there are many HP/Simpson panel meters with similar case and part numbers starting with 1120, but have different last 4 digit. Is there a way to find which meters have the same electrical properties, such as full scale current and resistance, and just different markings on the scale?
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Unfortunately not it seems and the 6177B & 6177C manuals give no details as to the F.S.D. for 1120-1147.
The 1120 is the HP part code is used for meters of all kinds, there are different sizes & case styles, the actual movements were made in standard linear, centre zero & logarithmic types, also some of the voltmeter scales were individually calibrated to the meter movement.
But you might get lucky & find the PSUs use similar small panel meters, with a different scale, just make sure the size is correct to fit the front panel.
David
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The 6177C 6181C manual gives two part numbers for the different scales, the 120V version (1120-1148) is available on ePay, question is can they be taken apart & the scales swapped without destroying the meter? You would have to go though the adjustment procedure afterwards too.
https://www.ebay.com/itm/124764961510 (https://www.ebay.com/itm/124764961510)
Then again is it actually burned out and not just a broken connection or some other problem inside? Or a problem with dirty contacts in the switching circuit, or an open circuit resistor feeding the panel meter.
The typical F.S.D. marked on the scale plate on some of the larger HP panel meters is 1mA, of course yours could be less or more.
I did manage to fix a different style of HP panel meter, where the hairspring had got crossed up with itself, be very careful if attempting any repair, non magnetic tools should be used. I've had many meters damaged (the plastic frame and/or the glass) by inadequate packing & shipping.
David
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This is a good find, it's probably as close of a model as one can hope to get.
I opened the meter, it's easy to replace the scale. It is an open circuit, I couldn't quite tell if its the actual winding open or one of the hairsprings is broken.
It seems 1 mA full scale is pretty common, but I was surprised there was not more of a standardization of the meters by full scale current and resistance. Probably in the olden days some repair shops would have a list of replaceable meters, but maybe it didn't survive to present day.
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I looked more closely, it is the hairspring that broke off at the solder joint. This is of course much more likely than the coil being blown, since the current source itself works fine.
But I messed up the hairspring trying to solder it on the inner joint by getting solder on other parts of the hairspring. So now have to buy a replacement meter.
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For future reference, the meter 1120-1148 has full scale current of 1 mA and resistance of 93 Ohm. It works fine as a replacement for 1120-1147 after change of the scale faceplate.