Motorola R2001c Manual
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Motorola R2001A Service Monitor - Maintenance Manual in Business & Industrial, Electrical & Test Equipment. * R2001D and R2001C series manual also available.
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Brand: Motorola Subject Area: Operations & Maintenance Equipment Type: Communications Test Equipment Country of Manufacture: United States Product Type: Manual Country/Region of Manufacture: United States.
Replacing the Power Supply Capacitors on the Motorola R2001B and R2001C Communications Service Monitors Replace the Power Supply Capacitors on the Motorola R2001B and R2001C Communications Service Monitors By Robert W. Meister WA1MIK Background: I acquired an R2001B for free because there was nothing visible on the display, and without it, these units are pretty much useless. A quick check revealed the CRT was completely disconnected. After plugging everything back in and splicing some wires, the unit powered up but the display text was extremely dim and I could see noise and saw-tooth squiggles running around the display; non-text scope traces were much brighter. Everything functioned though.
Power supply filter capacitors were suspect. After Steve K7LJZ did his, I decided to tackle mine. Based on the date codes on the ICs, my R2001B was made in 1981-1982. The power supplies in the 'B' unit are identical to those in the 'C' unit.
The full service manual for the 'B' model can be found on this website. The Low-Voltage Power Supply section from my 'C' manual (6881069A99-O) has been scanned to a. I have amended and corrected the scanned pages.
The High-Voltage Power Supply section has also been scanned to a. The R2002 is an R2001 with the IEEE-488 (GP-IB) option. Other R200X models are still the basic R2001 with additional features, such as for trunking and cellular telephones. You'll have to create your own capacitor list and procedures for the 'A' and 'D' models, but they are probably similar. I'll be referring to the R2001B as the Service Monitor (SM) from now on. Repair Techniques and Helpful Tips: These items apply to both power supplies and should help prevent you from getting into too much trouble. Protect the pins on the flat cable connectors; they are very fragile.
If you have some black anti-static foam that ICs often get shipped in, push the plugs into pieces of that foam and tape them up. Thick pieces of styrofoam will also work.
Do one board at a time. Remember the component orientation or print the pictorial so you can re-install them correctly later. Mark where each TO-3 device is installed. Clean the insulators, devices, and the chassis before you reinstall them. If there was any heat sink compound on them, put a thin film of new compound on the insulators.
I used a red 'Sharpie' marking pen and the marks wipe right off with alcohol and a paper towel, so be careful when cleaning the various devices. Mark all wires attached to external components (capacitors and diodes). Again, a red 'Sharpie' marking pen works great on the Teflon wires and wipes right off. Keep track of all mounting hardware (screws, washers, spacers, and insulators) so you can re-install it properly later. I usually store the hardware on the device (if possible). Note the orientation and polarity of the existing capacitors so the new ones go in properly.
The pictorials in some manual don't have all the polarities indicated. Print out the pictorials or take and print photos and mark those. Do one capacitor at a time so you install the correct value and can verify it's in the proper orientation.
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Check it twice; install it once. I used a temperature-controlled soldering iron set to about 700F (370C) and Kester 60/40 0.039 inch rosin-core solder. The printed circuit boards have large ground foils that will make capacitor removal more difficult. I suggest unsoldering the ungrounded lead first, and after that lead is free to move in its hole, heat the grounded lead and pull the capacitor out of the ground hole while the solder is still molten. It will now be much easier to remove the solder from the ground hole. I use a Solda-Pullt vacuum-plunger desoldering tool and found that the caps were extremely easy to extract.
I added fresh solder to some holes to clean them out better. Before re-installing any board, clean the flux off the solder joints using a toothbrush and 91% (or greater) isopropyl alcohol or a commercial flux remover. While you've got the boards out, check the diodes. These units use a lot of Schottky diodes, which have a much lower forward voltage drop than silicon diodes (0.1-0.4V vs 0.7V) and a lower forward resistance.
Motorola R2001 Manual
The stud diodes and TO-3 components usually have a light brown mylar insulator between them and the mounting plate. The manual says they're mica, but these are much more flexible. There was no heat sink compound on any of the components that used these insulators. After you work on modules with stud diodes or TO-3 components mounted to a metal plate or chassis, check for short circuits between their cases and whatever they're mounted to. Most of them are insulated and should NOT make electrical contact. Low-Voltage Power Supply (LVPS): This assembly is covered in Section 6 of the manuals and is known as A1. It consists of four plug-in boards (A1A1, A1A2, A1A3, and A1A4), a motherboard, and a chassis.
The LVPS is located at the rear of the SM. A 92mm 120VAC fan expels air out the back. The entire power supply assembly must be removed to do any repair work. While it was still in the SM, I measured the AC and DC voltages on the LVPS test points, located along the top edge of the boards.
Based on the amount of noise and ripple (AC voltage), I decided to replace the electrolytic capacitors on all four boards. I did NOT replace the two large screw-terminal capacitors mounted to the A1 card because they're very expensive.
I did have to remove them to gain access to the solder side of the A1 card. The table below has the DC and AC voltage readings on the LVPS test points with the original capacitors as measured with a Fluke 189 DMM to TP201. The real DC test points should have minimal (under 10mV) AC voltage on them. Some test points have 20-40 kHz signals on them so they should have a significant amount of AC voltage present; these have (AC) in the ' Signal Name' column. The first digit of the Test Point number represents the board it's on (1XX = A1A1, 2XX = A1A2, etc). The last two columns are the voltages after the capacitors have been replaced.