MC-1304 replacement

N

norla

New Member
Hello everybody, my first post here!

I have a Pioneer SX 770 receiver with a w13-024 MPX unit that does not work. Everything points to the MC-1304 IC being faulty so I would like to replace it. However they seem a bit hard to come by, so I was wondering if someone in here knows any good alternatives?

This thread (http://audiokarma.org/forums/index.php?threads/pioneer-sx-1500td.212410/) mentions a "CA3054, that crosses over as NTE 917", but I'm struggling to find something that would match that as well.

There are a couple of 1304's for sale at eBay but after shipping (to Sweden) it would cost me more than I paid for the amp. So any help is greatly appriciated!

All the best,

Mattias

Edit: spelling
 
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another cross to explore is the m5109p dual differential amp that superseded it on mpx board w13-026 that Pioneer recommended (the 026 board!!) as a replacement for the 024 board.

unfortunately that brings us back to CA3054, and the cross NTE 917 / ecg917 ...
 
Ok thanks, no easy way out I guess. Fun fact: the schematics say it should be a 026, but there is a actually a 024 inside the unit.
 
Thanks for the info/specs rcs16, might come in handy!
Found an MC1304P on eBay for 9 euros plus 6 euros shipping (something like 17 dollars in total).
Think I'll go for that.
 
The specs are really good, they show all the pins voltages on them too.
I could not find one on eBay.
I hope you can get the parts and it solves your problem. You might have to do some tuning of the tuned ckts, hopefully not.
 
Norla...Wow! I've had the identical problems on an SX770. Let us know if those ebay replacements worked! I've seen the listings you are talking about.
 
i just replaced my mpx board in a sx1500td with the upgrade w13-026 board. i, like you, got on ebay and bought an mc1304 ic, AND STILL NO STEREO LIGHT! with the the old w13-024 board. and while it sounded nice i couldnt hear any separation. so i spent 20 bucks and bought one on flea bay. it arrived yesterday afternoon, i recapped it and replaced the 2sc871 with a ksc 1845. i also replaced the 3 2sc870's on the fm muting board. success! i have a steady fm stereo light and separation that i can hear. i just finished it up an hour ago and remembered this thread and thought you would like to know. as far as the supposed discrepancy with 024 vs 026 i could Find NO schematic on line that showed the 024 board but could find several service manual's that showed that board, unfortunately,none of THOSE manuals had a "whole unit" schematic,
 
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Very interesting to hear that, thanks. Still waiting for my mc1304 to arrive so we'll see how it turns out. Mine seems to be completely dead.
The combined signal arrives just fine to the IC but there is nothing at all coming out of it.
 
well if it doesnt at least you have an "out", there was a seller on flea bay that was selling all the boards and switches for a 990 for 55$. i looked closely.and it had the later 026 board. its nice to find parts.but at the same time it seems a crime in a way to carve the things up.
 
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Ok, got the item from eBay today. With the IC pins sticking out of the envelope! Jesus christ...

Fil 000 (1).jpeg

I bent the legs into shape and installed the mc1304 and everything seems to work fine now. So problem solved I guess!
Still curious why it failed in first place, might start a new thread for that however.
 
JC is on your side, good job. The IC might be older than you are, it was a early 70's part. As to why the IC failed, shit happens :) .for example, dielectric breakdown, electro-migration, and a few more not worth considering. Enjoy.
 
Well I'm an early 70's part myself so I guess me and the 1304 are about the same age :)

Anyway, the reason I'm curious is that I'm a bit worried i might happen again. Here's the thing:

The excellent document you provided rcs16 specifies that the max voltage for the Stereo/mono pin (nr 4) is 2V. This pin is fed from pin 9 (MUT) on the FM board which seems to indicate the signal strength. However there is this weird peak around 98 MHz where there is total audio silence but the signal strength goes through the roof. The signal meter hits the bottom and the voltage on pin 4 on the MC1304 is over 3V. Which is way over it's range and might cause some damage I guess.

My theory is that this weird peak is caused by some fault on the FM board. I cannot see it on other FM tuners I have.

Or am I just being paranoid, reading the specs wrong or something else?
 
norla said:
My theory is that this weird peak is caused by some fault on the FM board. I cannot see it on other FM tuners I have.
Click to expand...
Not sure why that is.
I do not have a schematic for a W13-024, but I do see a layout for one in the owners/service manual, it has a 15K for R2. In the 1304 datasheet they use a 20K for a pullup to Vcc.
I do not think that the max V on pin 4 is 2V, it is the highest level guaranteed to switch to stereo.
 
Sounds reasonable. I'll put the cover back on, relax and enjoy my shining stereo light! Thanks again for all your help with this.
 
So I just replaced that mc1304 with an ECG718 that I bought online. Worked great. I was amazed.

In my case, it appears that the L+R path of the 1304 breaks, so when in FM mono, you get no output, in FM stereo you get distorted (but discernable) sound from the L-R path which stays working. That led me to waste some time looking at the muting circuit for the receiver. Realizing that I only got audio when there was a 19khz pilot available took a while... I have a schematic for the W13-024 if anybody is interested.
 
willy440 said:
So I just replaced that mc1304 with an ECG718 that I bought online. Worked great. I was amazed.

In my case, it appears that the L+R path of the 1304 breaks, so when in FM mono, you get no output, in FM stereo you get distorted (but discernable) sound from the L-R path which stays working. That led me to waste some time looking at the muting circuit for the receiver. Realizing that I only got audio when there was a 19khz pilot available took a while... I have a schematic for the W13-024 if anybody is interested.
Click to expand...
I would like a copy. Does anybody know what voltages should be present at all 14 pins on the MC1304?

Thanks -- John
 
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My first “stereo” back in the day (~1970, when I was a mere 16 years old) was based around the Pioneer SX-770. I remember the seductive blue glow of the pseudo-McIntosh faceplate. I sold it a few years later and “moved up” to ever fancier components.

Recently I’ve thought about replicating that old system (Wharfedale W60E speakers, AR turntable, Shure cartridge) for nostalgic reasons. When an SX-770 in nice cosmetic shape, but making no audio, showed up on eBay, I negotiated a price of $50. When I got it, I cleaned off years of grim to reveal a lovely unit in sweet shape. I cleaned all the switches and pots with DeOxit, and I checked a few voltages, especially at the speaker terminals for excessive offset. Everything now worked except for FM. A bit of troubleshooting told me that I needed a new FM demultiplexer chip. My unit is an early one from January 1970.

My MUX board, labeled W13-024, had a Motorola SC5199P chip in it. I can find almost nothing on-line about that chip. The schematic that I have for my MUX shows an MC1304P chip instead of what I actually had. That weird chip was original, with no evidence of de/re-soldering anything. My MUX PCB is laid out with the same pin-out as the MC1305P. But a few ancillary resistors have different values. So I found a NOS MC1304PQ on eBay and we settled on a price of $15 for it.

I popped it in (adding a machined DIP socket) and the damn thing now plays FM, stereo and all. Yes, everything now works. I have no doubt that I could tweak the resistors on the MUX board for improved separation, and better filtering of the 19KHz and 38KHz subcarriers. I’m also sure the receiver could someday benefit from replacing all the electrolytic caps. I have LED bulbs on order for the front panel lights.

The SX-770 has a pleasant, easy-on-the-ears quality. My favorite receiver, which I use in my workshop, is the Harman-Kardon HK 430, a marvelously vivid and punchy unit. By comparison the Pioneer sounds rather laid back, but it is not embarrassed by the comparison. Better to be laid back than gritty or hashy, I say.
 
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