Hi. This is my forst post here, so go easy on me
I've a Dynacord 2600 i'm working on. When it came in to me, it was blowing fuses, and I traced that down to 5 failed output transistors in the Channel A amp. I've replaced those, and now the amp will power up. In addition to the output transistors, 2 of the 2 way 0.33, 7w ceramic resistors were short <EDIT: Open on 1 side each, sorry I made a mistake there). I can't find those anywhere, but I've made my own x2 by putting 2 x 7w wirewound 0.33 ohms in their place, and checked they give the same values as the originals.
So here's where it gets funky. I get one of 2 scenarios when starting the amp now.
Scenario A: Amp starts, fans come on for 2 seconds, but the channel A High limiter LED is lit, as well as the Protect LED which goes out after a few seconds when a relay kicks in and the fans stop. The High limiter remains on, and the channel is innoperable. The other 3 channels (A low, B Low and B High) all work in this scenario. I've tested this with a 40hz, and 1khz signal as per the service manual. Amp is drawing anywhere from 130 - 300w in this state.
Scenario B: Sometime when switching on, the unit draws over 2KW of mains AC and the A amp high side gets hot real quick. When the amp is like this, I read 183V DC across the NPN/PNP sides of AMP A. It does not do this all the time, and most times, I get the previous scenario.
I've checked for shorts etc, and none found. I've checked all the filter Caps, they are OK, checked the relays, they are all fine and done general testing of diodes/transitors etc (admittedly, not thoroughly). With the Amps disconnected, I get the first scenario. Can't decide if the fault with the limiter is in the amp, or before it.
If anyone has come across an issue like this before, or can offer some constructive help, I would be eternally grateful.
Warmest regards from Ireland
Jimbo