McIntosh 4100 cap question

[eedork]

Hey guys -

I'm putting together a parts list for a full recap on an early model McIntosh 4100.

I've been working on the preamp board and came across some interesting caps that look like regular electrolytics, yet do not have a negative marking on the outer case. See the attached picture. Are these actually NPs? The ones circled in the picture are C707/C708 from the McIntosh service manual.

My plan is to use Nichicon Muse ES for all NPs and then a mix of Nichicon UPW (where regular blue caps are currently installed) and UKL (to replace the low leakage orange caps) for most other positions.

I may also use some Elna Silmic II or Nichicon FG in signal path locations, or possibly even Muse ES - I think I read something here where Muse ES can be used and is recommended for all signal path locations less than 10uF even if an NP is not specifically called for.

Does this sound reasonable?

Thanks!

-Matt

 

[mibag6]

See post 59 in this thread:
http://audiokarma.org/forums/index.php?threads/mac-4100-under-the-knife-qs.176380/page-3
There's a thorough list for the 4100 here.

 

[eedork]

Thanks! I saw that thread and the cap list.

That list uses BP caps in the positions I have questions on. Seems like it worked out fine, but I'd still like to understand what those caps are.

-Matt

 

[eedork]

Just a quick update. The caps in question are indeed NP - it says so right on the outer case of the cap, I just didn't see it the first time. The schematic does not explicitly call for NP in these positions, so it's possible the factory just used what they had on hand. Regardless, I will be replacing them with Nichicon ES just in case.

There are also two purple caps on each driver board that are interesting C801 and C823. Anyone have any insight on these? I believe they are just regular BP caps, but I'm not sure why they are different than everything else in the receiver.

Thanks!
-Matt

 

[eedork]

I've finished compiling my cap list for the 4100. I'm using Nichicon PW for most locations with KL for any orange cap replacements. Nichicon ES are used for all NP and signal path caps < 22uF with FG used for signal path caps > 22uF. I had to use a few Wima MKS2 for low value signal path locations as well due to unavailability of ES in these values.

I've attached my list. It may or may not be 100% accurate, but I will update it when the parts come and I start the recap. Note that I did find a few discrepancies between the schematic and the actual parts installed (C901, C902). In these cases I've substituted based on the installed parts.

Also note that my 4100 is an earlier model with a serial number less than BY3001. Newer units have updated FM boards and possibly some other changes. The cap list I've compiled is for the earlier units only. Grand total for all of these parts is just under $24 from Mouser when rounding up to a quantity of 10 on some values to take advantage of the price breaks. Not too bad!

-Matt

UPDATE: The attached parts list has been updated and should be fairly accurate now. For anyone that stumbles across this in the future, please double check it and let me know if you find any issues! No guarantees here ..

 

[eedork]

Here is the Mouser BOM for anyone that is interested.

"Mouser PN" "Raw Quantity" "Round Up"
505-MKS2B034701B00KO 5 5
647-UES1H3R3MDM1TD 7 10
647-UKL1E4R7MDDANA 6 10
647-UES1C100MDM 2 2
647-UPW1C470MDD 3 3
647-UFG1C470MEM 2 2
647-UES1H100MPM 8 10
647-UPW1E221MPD 4 4
647-UES1H2R2MDM 6 10
647-UPW1H100MDD 9 10
647-UKL1H1R5MDD1TA 2 2
647-UPW1V470MED1TD 4 4
647-UPW1C101MED1TD 2 2
647-UPW2A470MPD1TD 4 4
647-UPW2C100MPD 1 1
647-UPW1H221MPD6 1 1
647-UPW0J471MPD 1 1
647-UPW1E101MED1TD 1 1
647-UPW1E100MDD6 1 1
505-MKS2B041001C00MF 5 5
647-UPW1H010MDD1TD 3 3
647-UPW1H3R3MDD 3 3
647-TVX1C101MAD 1 1

UPDATE: This list has been updated for consistency with the revised parts list in post #5 above.

 

[eedork]

I've found an issue on the volume board of this 4100. The schematic says that C501 and C502 should be 0.47uF / 50V, but I've got 0.82uF / 50V installed. Any thoughts on this? I've ordered 0.47uF MKS2 for these caps. Can I use these or should order 0.82uF instead?

Thanks!
-Matt

 

[nj pheonix]

I'd tend to go with what you pulled.
Sometimes runs are tweaked during production.
Sometimes there are multiple manuals, or bulletins based on S/N
Sometimes just typos in the documentation or the silk screening on the board.
Unless you have a reason to believe there's a problem , I'd go with what you found.

 

[eedork]

Thanks!

I agree. I've found a few more discrepancies between the schematic and what's been installed, so it looks like I'll be placing another Mouser order. Here are the discrepancies I've found so far:

C501/C502 (volume board) - schematic says 0.47uF / 50V, but 0.82uF / 50V installed
C511/C512 (volume board) - schematic says 100uF, but 47uF / 35V installed
C901/C902 (tone board) - schematic says 100uF but 10u / 50V installed
C935/C936 (tone board) - schematic says 2.2uF NP, but 10uF / 50V polarized installed

EDIT: Unfortunately 0.82uF caps are hard to come by these days. I may go with the 0.47uF for now.

 

[nj pheonix]

I found these
http://www.mouser.com/Passive-Components/Capacitors/Film-Capacitors/_/N-9x371?P=1z0wpr5
As long as v is higher its ok.
If possible I'd use a film if it fit where an electrolytic was.
If it doesn't fit so be it. Caps are smaller now than when built.
If it was good enough for mac then, chances are its plenty good enough for us now.
The elytics were generally +/- 20% so I wouldn't make myself crazy.
You can parallel caps to create a value but I strongly suspect there are good subs available. If you can't source at a mouser or a digikey (or vendor of your choice) you more than likely get it direct from mac.

 

[eedork]

Thanks nj! I've used the 0.47uF for now, and will either stack two of them or purchase a proper 0.82uF cap as you've suggested with my next order. The 0.47uF seems to be working fine for the time being.

So far so good on the recap. The AUX1/2 and AM inputs all sound excellent with both channels working. FM is playing only from the left channel. I still have the AM and FM boards and the left and right driver boards to recap, and there are also two caps on a tag strip on the bottom and two on the power level indicator LED board that I'll need to replace. The relay seems fine, so I'm hoping the issue with the FM tuner is either a bad cap or a bad/weak connection to the preamp board. Note that I have been reflowing all Molex connectors as I've worked through each board.

The 4100 sounds great so far!

I'll update the parts list in my earlier post with any corrections once I'm done with this project.

-Matt

 

[eedork]

One more discrepancy. C1013 on the FM board is listed as 1uF in the schematic, but 0.47uF was installed.

I also tracked down the issue with the dead channel when listening to FM. Looks like IC703 is bad. This is an 8 pin op-amp (LM301). Fortunately Mouser still has some TI replacements in stock, but they are EoL and are discontinued. I'll probably order a handful to have on hand since there are a few more in the 4100 and I'd like to have some spares.

-Matt

 

[eedork]

Hey guys -

What is the correct part for the 4100 speaker relay? In my 4100 the installed part is a Magnecraft 78RCSX-II (24VDC), so I ordered a 24VDC Omron replacement. However, I have seen a few different posts here where a 48VDC relay is recommended, which leads to my question about the relay circuit.

The schematic is definitely a little confusing. The relay coil is driven by pins 13 and 14 on the power supply board, which should be at 16VDC and 40VDC, respectively, according to the schematic. What's inconsistent is that pin 14 is connected directly to the 48V supply rail, so I don't understand why the schematic says 40VDC on the block diagram. I'm actually measuring ~48V as expected at pin 14 and ~8V on pin 13.

So my (24VDC rated) relay is being driven by >40VDC instead of what should be 24V according to the schematic. EDIT - after a few minutes, the coil eventually sees ~48VDC. This can't be good for a part that is rated at 24VDC ...

Can anyone help me make sense of this? I'm wondering if I should have ordered a 48VDC relay instead because it seems like the factory one is being pushed a little hard.

Thanks!
-Matt

 

[nj pheonix]

If the coil is seeing 48v, you really want to have a coil with a 48v rating. I really have little experience with a 4100 specifically but 48v is 48v. It will cook the coil on 24v relay.

 

[eedork]

If the coil is seeing 48v, you really want to have a coil with a 48v rating. I really have little experience with a 4100 specifically but 48v is 48v. It will cook the coil on 24v relay.

Agreed! I don't think my relay likes the 48V it's seeing ... I took it apart to clean the contacts and the coil is discolored and there was a distinct odor when I removed the cover. My relay looks original, so it's lasted (surprisingly) almost 40 years. What happens if you run a relay way past its rated voltage? I assume at some point the coil will open up rendering the relay useless.

McIntosh made thousands of 4100s, which is why this is so confusing. The schematic is definitely inconsistent, but despite that I'd expect to find a 48V part installed, not the 24V part I've got.

Hopefully Terry D or c_dk will chime in and shed some light on this.

-Matt

 

[mibag6]

I can't tell you much but my 4100 has the same 24V Magnecraft as yours and it looks like new. I got the Mac from an estate sale so I can't say if the relay has been replaced at some time or not. I would expect the coil of the relay to fry in short order with double voltage on it.

 

[eedork]

Thank you for confirming that my relay is most likely original mibag6. Perhaps I have a fault on my power supply board then that needs to be tracked down. The only other components in the relay coil circuit are the two 'thermal switches' which I haven't tracked down yet. I'm not sure if they are on the driver boards or the power supply board.

At this point it seems that there is a fault somewhere since the coil should not be seeing 48V.

-Matt

 

[nj pheonix]

For sake of trying to get you best info, What's the S/N on that. Maybe i can match up a manual.

 

[eedork]

S/N is BY2155. Thanks nj!

I believe I'm using the correct manual.

-Matt

 

[nj pheonix]

In one drawing K1 is between 16v and 40v which would make 24v across the coil probable.