Correction: R2210B Well I answered my own question. I used acetone to gently rub off the 12B53 overwrite and the underlying marking were: MAC3040-25. Thankfully there is a datasheet on that part and it is a Triac (400v, 25A) and cross references to: NTE56016 and perhaps BTB24-400CW. BTW - I did chec...

Need assistance in identifying a semi marked 12B53 - I am repairing the LV PS for the R-2210C service monitor. Basically the R2200A maintenance manual has 99% of the info I need in repairing the LVPS, however the R2210C uses the RTP-4018 B LVPS which is slightly different from the RTP-4018 A a liste...

Update: On/off push button problem resolved. Previously, I could use the rubber push button to turn on the unit but I could not turn off the unit via the front panel on/off rubber push button. I took the front panel apart and discovered that the rubber button graphite had resistance in excess of 2k ...

Wowbagger I agree completely - this particular COM120B unit belongs to a small communications service company that I occasionally do work for and volunteered to help out - what I do not know if anyone else had their hands on the unit. Initially the problem in the power supply was blowing fuses after...

Yes, I connected a 12vdc power source alone and cannot turn off via the front on/off push button. In either case (AC or DC) it powers on as advertised, but have to use the rear AC rocker switch to shut off the unit.

Thanks Wowbagger; I checked a dozen times and I just don't see it - the front panel cables seem in place and correct - This model uses a PCB and resistance push buttons for the front panel and then connects to the interior Audio PCB via a DIP header - no numbers on the header but I did find both con...

Sorry for the delay, life got in the way: Ok, I ramped up this project again, I replaced the Vicor VI-262-EU module - still same results - checked all components, caps (pass ESR test), doides, etc and they all show functional so I focused on the AC to DC module. In this set it is a Powercube UNV300/...

Correction to the previous post: The Vicor VI-262-EU brick is 300V in - 15V out at 250W and the Powercube AC to DC brick is 88-230VAC in - 300V out at 750W.

I connected the DC power supply and had the unit running for an hour without any problems. Self Check shows all test passed. I checked the 300V caps with a cap analyzer and also checked ESR - in both cases the caps showed good. Since I have the PS out of the unit I decided to order the DC to DC modu...

Wowbagger - I checked and the optional amplifier and it is not connected. However, I need clarify my previous statement regarding the GEN Mode blowing the fuse - the fuse blew on two previous occasions when I depressed the GEN Mode button, but I have not been able to recreate the same scenario so I ...

My friend has an IFR COM-120B and has been using the unit as a bench service monitor for several years without any problems. Recently, the unit developed a problem as follows: when you depress the GEN Mode switch the unit blows the 2A AC fuse in the power supply. Replacing the fuse the unit starts u...

RE: 1300MHZ IF RX - the 5.6 ohm resistor and a few pin diodes turned into carbon dust. No doubt someone pumped quite a few watts into the Ant port. The MA47047 pin diodes are difficult to find so I used A5S303 pin diodes as a sub. They are basically the same except 100 reverse voltage instead of 200...

just an update: the new rewind is working great - filament supply at 5vac, B+ at 210vdc and for the HV measuring I used a Tektronix 40Kv probe and 1v setting on the scope so the HV seemed to be around neg 2300vdc. Best of all - no audible transformer hum or buzz. I used epoxy on the windings so it s...

jry Thanks for the info. I have the older version that uses the feedback windings to a relaxation oscillator. No filament resistor and yes, I certainly wished I had the chopper oscillator version - a much better design. I'll look through the service manual and this time read through slowly to see wh...

Does anyone know the rated filament voltage for the IFR1500 CRT (V6401)? I am winding the HV transformer from scratch and used the number of turns as specified in the service schematic. For the filament 2 turns are listed and that gives me 5vac. If the filament voltage is greater than 5vac then I ca...