positive emitter coupled logic (PECL) signal/input voltage - Page 1
Forum section: electronics / repair

author: sae-7125
author_rank: Newbie
timestamp: October 22, 2022, 06:04:56 pm
content: in the process of diagnostics for a circuit that feeds a fairchild 9528 16 pin chip. its an oldie #vintage circuit design. there is a 1975 data book giving minimal specifications and no indication of input signal levels, voltages for high low as well as power supply limits.http://bitsavers.trailing-edge.com/components/fairchild/_dataBooks/1975_Fairchild_Full_Line_Condensed_Catalog.pdf[page 215]from what is measured and circuit design its a pecl being fed +4.1vdc. circuit involves 100 megahertz region (fm band tuner). output from the tuner gang fets and fet buffer still seem insufficient but not knowing what the 9528 is looking for makes things worse to troubleshoot.thought, ideas anyone? a royal pain in the pecl scenario..

author: sae-7125
author_rank: Newbie
timestamp: October 22, 2022, 06:49:58 pm
content: some informative sites:https://www.elprocus.com/emitter-coupled-logic/https://www.allaboutcircuits.com/technical-articles/the-basics-of-emitter-coupled-logic-ECL-inverter-buffer/

author: edavid
author_rank: Super Contributor
timestamp: October 22, 2022, 06:52:30 pm
content: The 9528 datasheet is in this databook:http://bitsavers.trailing-edge.com/components/fairchild/_dataBooks/1971_Fairchild_9500_Series_Easy_ECL_Family.pdf

author: sae-7125
author_rank: Newbie
timestamp: October 22, 2022, 07:32:42 pm
content: it looks like pdf pages 47 and 48 have useful info. unfortunately there are no examples of a positive ecl circuit and how it would affect the logic level high/low amplitudes.if using 5v or 4.14 vcc instead of -5.2 vee changes -1.14v high and -1.45v low to some other value, although the delta of 0.31v is interesting to note. i wonder if 4.06v high and 3.75v low would be correct/accurate for a pecl circuit?

author: edavid
author_rank: Super Contributor
timestamp: October 22, 2022, 10:56:29 pm
content: No, ECL thresholds are relative to the positive supply, so they would be VCC- 1.14V and VCC- 1.45V, so +3.00V and +2.69V.I'm surprised it's not AC coupled though. Why don't you post the relevant part of the schematic?

author: sae-7125
author_rank: Newbie
timestamp: October 22, 2022, 11:49:27 pm
content: good to know. i would post a schematic if one actually existed. the nixie frequency counter i am working with inside a vintage early 70s fm tuner was apparently sourced from another company. just like the multi fet tuner gang made by gorler of germany.unfortunately the tuner gang and fet buffer daughter board schematics are for a slightly newer version vs what i am working on since some of the parts and voltages dont line up. the "b" version of the fm tuner system used a 74s112 instead of 9528.here is a rater crude chip number layout that required special surgery to create:nixie nixie nixie nixie7441 74417490 7490 9093 74939022 7400 7490 74909528 7404i have been adding to a thread over at:https://audiokarma.org/forums/index.php?threads/sae-mark-vi-tuner.898661/page-6the nightmare continues.

author: sae-7125
author_rank: Newbie
timestamp: October 23, 2022, 04:57:47 pm
content: nixie board layout, rf inputs near bottom of photo. 150pf input capacitor connected to pin 15 of the 9528. potentiometer controls dc level/offset for rf input. 18 ohm resistor next to chip reduces 5v supple to 4.14v vcc on pins 4 and 5.