Sencore MX129/  Advice on how to assess an ECG160 (2n1178) - Page 1
Forum section: electronics / repair

author: watchmaker
author_rank: Unknown
timestamp: February 15, 2025, 12:57:45 am
content: I bought this expecting to do some work. I found the SM on line before I pulled the trigger. I spent the day identifying the adjustment resistors and verifying some waveforms. Some of the waveforms have issues, but that comes later.Composite, SCA, Modulation, 10 and 1000Hz signals are generated and levels can be adjusted. No RF output.This unit is an interesting mess. Some of the joints were NEVER soldered. Then there is the fact that a previous worker was a slob (and he wanted to work on FM stereo??). Several dangerous solder joints and it looks like he wound up at the same transistor as I did because the traces are lifted off the board.So the first order of business is to get RF (although it can just be used for MPX). Then will come trying to correct waveforms in the first stage and then comes trying to correct whatever adjustments he played with. Better than a crossword puzzle.My current issue is assessing a 2n1178 transistor with 4 leads (ECB and Is). I managed to find a datasheet and it looks like an ECG160 will work. I found it crosses to AF106/109R/360 but those have lower max Vs on one or more of the specs.I have the RCA manual with the 2N1178 specs, and have looked at several cross reference books.So can anyone tell me how to assess these 4 lead transistors?And I suppose I might as well ask: Does anyone have a 2n1178 they can give up?Also there are some 1.0 MF 400 v paper caps. What can I replace these with?THANKS!!

author: coromonadalix
author_rank: Super Contributor
timestamp: February 15, 2025, 03:12:32 am
content: NTE 160 supposed to be equivalent too with a grain of salt,but you have the s pin, not sure, if i'm not mistaken it was only connecting the case, the other 3 pins where the ones you need2N1177 NTE1602N1178 NTE1602N1179 NTE160R-497A NTE1602N1527 NTE1602N1525 NTE1602N1525 NTE1602N1525 NTE160attached service manual schematics

author: watchmaker
author_rank: Unknown
timestamp: February 16, 2025, 12:11:16 am
content: Quote from: coromonadalix on February 15, 2025, 03:12:32 amThanks!! I already found the manual (Internet Archive) and downloaded it before I pulled the trigger ($50).OK, below is screenshot of the curve family from the original 2N1178. Nothing wrong with it; is identical to an ECG160 I had.Back in it went; but I should have taken pics. I think it was installed incorrectly. I relied on the schematic and ohm meter to reinstall it. The Pic of the schematic shows the problem area. As noted, everything works up until that very last stage. And the voltages on that transistor seem close enough.There is also a screen shot of the trace from the composite out. The trace responded to any and all front panel adjustments.The SCA signal is 78Khz instead of 67 KHz. So someone definitely made "adjustments".Senocore's rep is very well deserved. Every time I moved the board another lead came cleanly out of its soldered thru hole; at least those that WERE soldered.So now I am thinking caps in that last stage. I did check the RF out lead and it is 180 ohms on the conductor and also on the shield. Made no difference if I probed at the lead/pcb joint.I least have the major problem localized. Then I have to readjust the thing.

author: factory
author_rank: Super Contributor
timestamp: February 16, 2025, 09:16:20 pm
content: Looking up the 2N1178 I see pictures of those infamous four leg transistors, that are known for growing tin whiskers that cause internal shorts. The AF11x series commonly found in old radios over here are the most well known in this package, NASA took one apart to investigate;https://nepp.nasa.gov/whisker/anecdote/af114-transistor/index.htmlThe TVT equivalent book gives AF178, 40244 & 2SA118 as possible alternates.For the wax paper capacitors, use some modern plastic film types, they are still made in axial form.David

author: coromonadalix
author_rank: Super Contributor
timestamp: February 18, 2025, 05:37:59 pm
content: woah never heard about this phenomenon thks

author: watchmaker
author_rank: Unknown
timestamp: February 18, 2025, 05:49:10 pm
content: Quote from: factory on February 16, 2025, 09:16:20 pmThanks. I remember a photomicrograph from the 50s showing this. It is one of the reasons my shop teacher was biased (pun) against transistors.I am making progress.Replaced a cap in the final stage (maybe the right one? 4pF or should it be 4nF?) and now I get nice clean traces. From the looks of it, I need to adjust the main RF inductor, but it might be on the mend.Any comments greatly appreciated. I am using this to relearn troubleshooting and also basic RF theory.

author: watchmaker
author_rank: Unknown
timestamp: February 20, 2025, 12:16:58 pm
content: RF WORKS! Adjusted it to 100MHz with scope. Set an FM radio to 100MHz and got the tone. Need to find a stereo radio; might buy a Nakamichi clock radio (remember when Nak was the new McIntosh?)

author: t1d
author_rank: Super Contributor
timestamp: February 23, 2025, 04:01:39 pm
content: Quote from: coromonadalix on February 15, 2025, 03:12:32 amI scanned through this thread, to see if I could help. But, to be honest, it is outside of my knowledge base. One thing I might be able to offer is this bit of information... I recently read that NTE has gone out of business. IIRC, some of their suppliers did have some remaining stock. You may have to find other components to make substitutions. I hope this helps. Also, watch out for an increase in faked NTE parts, now. Scammers will be jumping in and charging crazy prices, for renumbered trash.

author: watchmaker
author_rank: Unknown
timestamp: February 24, 2025, 01:40:05 pm
content: Quote from: t1d on February 23, 2025, 04:01:39 pmThank you for making the effort!I have repaired it using the original transistor. It was an open cap although there a host of other issues, many Sencore related (wires popping cleanly out of their solder joints, connections that were never soldered) and attempts at repair by a previous lost soul. But it now generates an FM MPX RF at 100MHz.I bought many ECG/NTE components NIB over the last 2 years and have an inventory organized around the ECG system. Also have the book and lookup program.NTE prices have now gotten silly because of the business closing and I agree, it is important to be skeptical of anything that is not in sealed bag.After seeing some projects that used 1206 SMDs on the thruhole protoboard, I am now heading in that direction. Would seem to help control patristics.