SHP Fireproof Resistor

[paradisecs]

Troubleshooting a SHP3 amp. It gets sound only from the tweeter on the right side.  I pulled the driver board and it has a bad R98 (100 Ohm Flameproof 1w).  Upon it's death it left a smoke streak across the entire board.   I don't see any other burn spots or obvious bad caps or resistors.  I've tested the remaining resistors on the board and all seem to be in spec.  I'm going to replace all the lytic caps (someone replace some but not all previously)  and probably the other three flameproofs.  What damage could this have cause elsewhere and is there anything else to check before applying power after the new parts?  What would cause that particular resistor to smoke?

[robnyc]

This is/was very common. The output transistors on the affected channel shorted and usually took the drivers out for a smoke too.

It is a bigger job than just replacing resistors. First read this doc: www.flippers.com/pdfs/HudsonsBayWholesale_SeeburgSHP&TSA_ServiceNotes.pdf Then assess your skills and equipment -you really only need a good DVM w/diode test function.

Schematic's are here: www.verntisdale.com/Seeburgschem.htm I believe he sells kits of capacitors.

Aside from the needed mods outlined in the above article, I suggest not using more than a 1-1/2 amp slow fuse and NOT the 3.2 stamped on the amp. That bizarrely overrated fuse is one of the reasons why these flame so violently.

When I dealt with these i at first added B+ fuses to the plus and minus supply to each channel's finals. This was going a bit further than needed but these amps were used in a machine where they rested face up and ran almost always flat-out. Those emitter resistor would sometimes burn holes through the board and circuit traces would fuse out as well.

Be sure to test the machine speakers for shorts before reconnecting the repaired amp. ALWAYS test amp first with a current limiting bulb, i use 40w and start at minimum volume.

Ron will probably have something to add here.

RobNYC

[paradisecs]

Thanks for the link. I'm going over my SHP Amp guide and forgot about the HudsonBay stuff. I knew it wouldn't be as simple as I'd hoped and I've avoided working on any major amp issues so far but guess I can't wait any longer.