This McIntosh MC2155 power amp was brought in for service. The customer said the amp had a channel cutting out, and had some lamps out behind the meters. He also said the meters seemed slow or “sticky.”
The MC2155 is an early ’80s 2-channel amp, rated at 150 WPC (likely a very conservative number), and looking around the internet for info… it seems to be a somewhat rarer amp from McIntosh. It was only sold for a couple years whereas some of their products have 7-8 year runs.
When the amp was tested at our store, as all electronics brought in when demonstrating a problem at home, it worked great! It played both channels and the meters bounced accordingly. The lamps were out behind the meters, however. We discussed a service plan with the customer and decided to recap the unit and convert the lighting to LEDs.
The unit arrived in great condition for its age, and didn’t show any signs of previous service, destruction, or mishandling. You can see on the left, that the lamps behind the meters were partially out. Conversion to LED lighting will prevent heat buildup against the meter housing, and also give better, more reliable lighting.
(The original board on the above left, and the recapped board to the above right)
The driver boards, connected by a few nuts and some wiring harnesses, pull right out. The light blue, original Nichicon electrolytics were pulled out and replaced with Nichicon PW (high temp/high reliability). The smaller light blue one on the right by the blue potentiometers, replaced with a Nichicon MUSE bipolar cap. The original orange, low noise electrolytics were replaced with low noise Nichicon KL series and WIMA film caps. — On the right, you can see the parts that were swapped. Many of the parts we use for restoration are what McIntosh uses today in its current production units… Sometimes we use even better parts (film vs. electrolytic in the signal path)!
The before (left) and after (right) pictures of the Power Guard board, located behind the right side of the faceplate. Nichicon PWs used again in the filtering sections, and Nichicon Fine Gold capacitors used in the low noise sections (yellow capacitors).This board seems to get warm, so the high temp PW capacitors will benefit the amp in this area particularly.
The meter drive board got the same treatment.
-The light blue filters were upgraded to high temp KW
-The orange low noise upgraded to low noise KL.
-The bipolars changed to MUSE caps.
This should help meter move more freely and accurately.
These two bipolars (likely coupling caps) on the inputs are quite hidden, and difficult to get to.
After unsoldering the signal plugs from the RCA jacks, access eases up but it is still tight. They were again replaced with Nichicon MUSE bipolar electrolytics.
Lastly, lighting was addressed. Some of the original, fuse style lamps behind the meters had burned out. Due to the heat that the original bulbs put out, the plastic gets brittle. On the left, you can see the brown spots from the heat of the original lamps. Being that the tabs that hold the plastic housing are meant to be slightly pliable so they can be pushed into position, this makes removal tedious as they will snap easily and prevent them from holding afterwards. Luckily, we were able to remove them and put in LED lamps and reinstall them with great care. The lamps behind the wording was also changed to LED, with slight modification to the LED bayonets to fit.
The end result looked amazing!
*Unfortunately not many pictures were taken as focus was directed towards not snapping the housings! (before, above left, and after, above right)
The original main filters caps were pulled and tested for capacitance, leakage, and ESR. They tested perfectly. As appropriately sized replacements were not in stock, we left in place for now as they tested as good as new.
Upon completion it looked, worked, and sounded amazing! In our opinion, one of the nicer vintage McIntosh power amps our there. It is ready for another 3 decades to come!