McIntosh MR-78

[ChuckA]

Does anyone know the "off the shelf" part number for the balanced mixer IC used in the MR-78 tuner? Or a source for an original.

I'm working on one that has gone really "deaf" and everything points to this part. I thought maybe it was a MC1596G but pinout is different.

Thanks

 

[AbSoundLabsMN]

Hi Chuck...

Since the IF Limiter and detector use three IC's, I was wondering if you can advise me which IC is involved. The Service Manual indicates that they are IC-01, IC201 and IC-202. It would also help if you can give me all of the writing on the IC, in question.

Mark
McIntosh Factory Service Facility

 

[ChuckA]

Mark
It's the only IC in the tuner section, labeled as IC1 on the schematic. No markings on the can.

Chuck

 

[clinic-audio]

IC1 is a 133-006 commercial type LM371 from National semi conductor but don't tell to anybody it is secret

 

[c_dk]

The actual McIntosh part number is needed for the cross reference......133-xxx. I don't know that it is a secret but I will say I don't trust my memory anymore without the part number.

 

[ChuckA]

The McIntosh part # is 133-006 but LM371 is definitely not the commercial part number.

Chuck

 

[c_dk]

My cross reference from 1992 shows LM371 as the commercial cross for the 133-006. So does the one from 1986 except that a 133-003, a CA3028B, was discontinued and a 133-006 was the sub for it, a LM371.

Have you checked with Mac parts?

 

[clinic-audio]

The McIntosh part # is 133-006 but LM371 is definitely not the commercial part number.


You are of course talking about voltage reg no me ! IC 1 has 14 pin , " your " LM371 3 !
If you know much better than I , I have nothing to add

Good luck

 

[clinic-audio]

My cross reference from 1992 shows LM371 as the commercial cross for the 133-006.

Mine is from JUNE 1973

 

[AbSoundLabsMN]

Hi Everyone

The part your looking for is McIntosh Part Number 133-006, Its schematic designation is IC-1. The Jedec Number for this IC is LM-371.

Regrettably, it is no longer available from the McIntosh Parts Department. Since this part is not normally defective, I don't have a secondary source for a replacement.

Mark
McIntosh Factory Service Center

 

[ChuckA]

I found the CA3028B data sheet (RCA 1983 data book) but it is an 8 pin differential amplifier. The 133-006 has 10 pins, so I can't see how that part was usable. Does anyone have a data sheet or link for the LM371? All I can find in current data sheets is an LED and LM371 isn't listed in the 1980 National Semi data book.

Chuck

 

[clinic-audio]

 

[clinic-audio]

picture of the IC in unit



if we watch closer we can read 006 (Mcintosh part number end) and "7014" before

 

[ChuckA]

Thanks for all the feedback on my request, but what I need now is the datasheet for the LM371 part. I've had no luck locating one as any search turns up a different type of part. Looking in old NS books part numbers end at LM358 and then continue at LM381.

Chuck

 

[c_dk]

Here is what my 1992 semiconductor cross reference says:

133-003 can be subbed by a 133-006.......the 133-003 is a ca3028b differential/cascade amplifier.

a 133-005 can be subbed by a 133-003....the 133-005 is a ca3053s a differential/cascade amplifier

the 133-006 is listed as a LM371 a balanced mixer with 10 legs the other 2 have 8.

Maybe two legs are not used, I do not know, you have to invent a solution sometimes with these 4 decade old units.

Let us know what solution you find because it appears Mark, Patrice, and myself with over 100 years together have not seen this part fail. Gosh if Terry jumps in we might make 150!

Off to be a grandpa!

 

[clinic-audio]

Yes , Chris , you are right , I never saw this problem .
I found the data sheet from National Semiconductor and the IC is LM371H
If you type the H after LM371 you will find it too .I do compare this commercial datas and they look pretty closer to original Mcintosh data
Delete this ic is not really easy and you have to be very very carefull .
What was symptom on your MR78 ?

 

[ChuckA]

My determination of this part being the problem is based on all other parts in the tuner testing good. And this part is the only one that has a major discrepancy on pins 4 & 6. Schematic indicates 1.6V
on each and I only have 0.3V.

Chuck