Working on a MC2500...

[eiraved]

I've reinstalled the lower cover and tested my work on the amp. No magic smoke, so that's good!
Oh yes, using the new to me C32 preamp and iPod for music, I tested for sound on a pair of Minimus 7 speakers. Sounds great! Unfortunately the right meter is now inop. I'll troubleshoot once I flip the amp right side up with the help of my strapping young sons!

 

[damacman]

Nice work! Do either of the amps have side rails or do you plan to rack mount them?

 

[eiraved]

Nice work! Do either of the amps have side rails or do you plan to rack mount them?

Thanks! Unfortunately only one amp has the side rails . I have some ideas on what I want to do, but haven't come to any conclusion on how these will be presented. I have my Niles Audio SVC-4 speaker selector and still feel I'd like to integrate and alternate between the McIntosh SS amps, my mono tube amps and four speaker pairs. I have time though, so once I finish both MC2500 amps and the C32 preamp I'll side by side them with the tube amps and then see if I want to keep the tubes as part of the garage system. I'm not into playing very loud music, so the tube amps will stand a fighter's chance, LOL!

 

[damacman]

I have my MC2300s mounted in a studio rack ...

 

[eiraved]

I have my MC2300s mounted in a studio rack ...

Is your rack on wheels? Got pictures of it here on AK?

 

[damacman]

Is your rack on wheels? Got pictures of it here on AK?

Two threads: http://audiokarma.org/forums/index....&c[title_only]=1&c[node]=54&c[user][0]=143153

 

[eiraved]

Nice! Something to take into consideration...

 

[eiraved]

Just finished recapping the Meter and Power drive PCBs. Powered her up and no smoke...
Next up is removing the eight heatsinks, removing the transistors from the heatsinks to clean and apply fresh thermal compound. I also removed the oxidation and brushed DeoxIT on the transistor pins before reinstalling. Gotta be careful and not overtorque the screws when installing the heatsinks because the heatsink brackets are made out of plastic and over time have become brittle.
Three heatsinks completed today, five more to go...

 

[eiraved]

Unfortunately the right meter is now inop.

I found a bad solder job at the wires connected to the right meter. Re-soldered the wires and voila, meter is now operational!

 

[eiraved]

the Rich Andrews mod for lowering the noise floor which involves relocating the overheat switch and re-routing the fan and overheat switch wiring.

Unfortunately for me and unbeknownst to Rich, this mod is more easily accomplished by just removing the two heatsinks involved with the modification. Remove a total of eight screws (4 per heatsink), remove heatsinks and now you have easy access to the switch. Unscrew the switch and re-install on the recommended heatsink while it is in the palm of your hand! Re-install the heatsinks, re-route and re-attach wires to the switch and you're done! Nothing more than a plain old screwdriver is all that's needed to accomplish this mod re-using the original screws.

 

[eiraved]

I've completed the recap on one MC2500 amp (except for the filter caps) and am awaiting replacement LEDs. I decided to compare amps to see how the recapped amp compares with the untouched amp, using ML-1C speakers and the recently purchased C32 preamp. I set the amps and speakers up for a mono-bridge connection and game on!

Strange, but the recapped amp appear slightly noisier than the untouched amp with no source applied and preamp / amp volume controls on full. I must note that to hear this I had to place my ear inches away from the speakers. Fortunately I don't play music at ear-splittng levels so I wasn't overly concerned about it. When I applied music via iPod source, the recapped amp was noticeably clearer, slightly louder and more musical than than the untouched amp. That made me think...the reason the recapped amp was slightly noisier with no source is at least partly due to the fact that it now plays slightly louder than the untouched amp.

 

[clinic-audio]

132-209 is MC2255 driver and not MC2500 Power transistor ....Don't you found any other ?

 

[eiraved]

132-209 is MC2255 driver and not MC2500 Power transistor ....Don't you found any other ?

The transistors shown in post #48 were what was installed on the amp when I received it. According to the MC2500 schematic, those 132-209 transistors are correct for positions Q713 - Q715 and Q913 - Q915. Is there some service bulletin or other document which says differently?

 

[clinic-audio]

No , no service bulletin , just my knowledge on MCINTOSH products .
output power stage is here (all MC2500 model and take care about serial numbers because drivers are not the same ) and if you read carefully you will see driver ref are 132203 and 132204 depending serial numbers ! output transistors are 132188 and 189


If you have any doubt , contact the factory

 

[eiraved]

Thanks for the information but you've raised some questions because you say the callout for the 132-209 on the MC2500 schematic parts list below is incorrect. Also, the transistor symbol numbers on your picture don't agree with the symbols on the McIntosh MC2500 schematic pages below. I'm sure you have a MC2500 schematic which matches your symbols, would you please share this with us?

EDIT: I've opened the second MC2500 in preparation for the recap and found 132-208/9 transistors installed on the heatsinks as well, but also found some MJ15003/4 transistors installed. In case you wanted to know, I purchased both amps from two completely different sources.

I imagine the MJ15003/4 are the replacements for the 132-208/9. Is your recommendation to replace all 132-208/9 transistors with MJ15003/4? If so, for what reasons? Please remember that both amps had no outstanding issues prior to the recap.

 

[clinic-audio]

Yes , but I made a mistake when I answered you , (my memory is not perfect ) 132209 is not driver for MC2255 but power transistor for MC2255 ;
when I saw your heatsinks with this transisitor , I remember that this is not the right one (see my previous post ).
You did not precise serial number's of your both units but the picture you have posted are right depending serial numbers of these units (again) check with your parts list and mine and you will see that we are talking about the same thing .
132-208 is a MJ15003
132-209 is a MJ15004
Don't forget that there is 5 types of MC2500
1) CS1001 to CS1487
2) CS1488 to CS2103
3) CS2104 to CS3699
4) CS3700 to CS3899
5) CS3900 and above

for all these models the driver boards are differents and transistors are differents , watch carefully serial numbers

 

[eiraved]

Thanks you very much for that helpful information! I was hoping for it as there isn't much information online in regards to MC2500 restoration. The serial numbers of my units are relatively close, CS2719 and CS2941, which would place them in the #3 group of your post.

I have about a dozen MJ15003/4 transistors available from a group purchase I did for a previous amp modification, so I can replace transistors if needed.

On my post #51, I indicated the untouched amp was quieter at the speakers with no source applied than the recapped amp. I checked DC offset on the untouched amp and it was just above the acceptable range at 4.2 and 4.6 mV. The recapped amp is 2.0 and 2.4 mV. One would think the untouched amp with the higher DC offset would be the noisier amp, but it's the quieter in this case. I'm wondering if the difference in noise is due to the addition of the newer MJ15003/4 transistors on the quieter (untouched) amp?

Please note the term I use, "untouched amp", is only in reference to the fact that I have not touched the amp. It obviously has been touched by someone due to the mix of 132-208/9 and MJ15003/4 transistors!

 

[eiraved]

The LEDs have just arrived via USPS (yay!) rather quickly via purchase from the bay. For those who don't know, my "secret" for quick shipping on the bay is to sort my searches by "nearest first" and find a seller who lives nearby. The LEDs were shipped Saturday and arrived Monday because the seller lived less than 100 miles from me in CA! Had I purchased from someone on the east coast, I would have received the LEDs at the end of the week.

I installed the LEDs on the meters and they are impressive, brighter than the originals! I replaced the Power Guard Limit and Normal lights with LEDs as well. I turned on the amp to test them and now the Power Guard Limit lights stay on all the time(?). These lights were off with the original lights were installed. I wonder if this an issue related to LEDs? I searched throughout AK and couldn't find an answer, so I guess I'll begin troubleshooting tomorrow.

 

[eiraved]

I found a 27pF ceramic cap on the 045620 input level / mode selection board, soldered between #3 and #5. Both #3 and #5 go directly to the 045928 preamp input / headphone output board, with #3 to the inverting input and #5 coming from the left preamp out. There's no cap shown in this location anywhere on the schematics. I checked the other amp and it does not have a cap installed at that location. Is anybody aware of a modification in this area which adds this cap?

EDIT: Duh, I found it in the schematic after all, but I don't see why it's installed on one amp and not the other. It doesn't appear the amp serial numbers are an issue here.