My HP 400F bit the bullet the other night. Upon closer inspection the -9V that is supposed to be present on the meter drive circuit was at -2V. I had a big voltage drop across R69, I expected a blown Q16 but as it turned out C39 is partially shorted. I lifted one side of C38/C39 and C39 is 420 ohms, C38 measures about 1.5 Mohm. I left C38/C39 lifted and when powered up I now have -8.1V on the meter circuit.
So I know from my brief bit of researching that these old tant caps are extinct. I'm not too concerned with high frequency measurements, I typically have the 100kHz filter in circuit. Anybody have a recommendation for a replacement for one of these blown tantalum caps? Just a modern bi-polar electrolytic or maybe back to back polars?
Even though CR22/CR23 measure okay I'd also like to replace them just to be prudent. The older version of the 400F manual (My 400F is a late model dating to around 1983) lists these as 1N4392 diodes which are also extinct. Has anyone had any experience with anything else to substitute for these meter diodes?
I included a pic of the schematic.
So I know from my brief bit of researching that these old tant caps are extinct. I'm not too concerned with high frequency measurements, I typically have the 100kHz filter in circuit. Anybody have a recommendation for a replacement for one of these blown tantalum caps? Just a modern bi-polar electrolytic or maybe back to back polars?
Even though CR22/CR23 measure okay I'd also like to replace them just to be prudent. The older version of the 400F manual (My 400F is a late model dating to around 1983) lists these as 1N4392 diodes which are also extinct. Has anyone had any experience with anything else to substitute for these meter diodes?
I included a pic of the schematic.
Attachments
The type 150D tantalum capacitors are still available from Mouser.
150D396X9010B2B Vishay / Sprague | Mouser
The 1N4392 diodes are listed in the Motorola 1966 semiconductor book as special purpose. They appear to be very high speed and very low leakage. Motorola did not make them and it appears they were made by a division of Hughes Aircraft. If they measure ok, it would be prudent to not replace them. The nearest similar part, also obsolete, is the Fairchild FD700. Again, replacement of the 1N4392 is not recommended.
150D396X9010B2B Vishay / Sprague | Mouser
The 1N4392 diodes are listed in the Motorola 1966 semiconductor book as special purpose. They appear to be very high speed and very low leakage. Motorola did not make them and it appears they were made by a division of Hughes Aircraft. If they measure ok, it would be prudent to not replace them. The nearest similar part, also obsolete, is the Fairchild FD700. Again, replacement of the 1N4392 is not recommended.
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