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ca7922303

hd130 no output hum only

Need help troubleshooting hd130 (chassis no. 2100-130) no output/loud hum. Thanks.

admin
admin's picture

The problem could be Filter Caps or Rectifiers

I see the post fine and checked your account and you are not blocked as far as I can see.  All hum and no signal could be bad filter caps, bad rectifier, bad tube(s), broken ground wire, etc.

As always, the power supplies must be checked first.  If the amp has never had a cap job it is probably time for it!

Steve

mm210
mm210's picture

Posts blocked.

I sent you an email with a fix for the time being. Try that and let me know. Mike.

ca7922303

hd130

Looks like it has new filter caps. Seller said it did. Came with no tubes so I bought (4) new matched EH-el34's. Don't have a brand new 12ax7, but had a few and change out and no effect. Don't see any broken ground wires. I bought this off of ebay to repair. It initially had low distorted output on both channels. After taking the two screws off of the bowed up rectifier board to see what I could do too straighten it out. I then had a 55k resistor at the bottom left of the rectifier board disconnected, so I resoldered it and turned it back on and blew the fuse. Put another fuse in and turned it on and now no output except for a loud hum with no affect to the hum by any of the controls. Also noticed a puff of smoke coming from power tube on far right of amp if looking at the back of the amp. Farthest from the transformer. Any ideas would be appreciated. Have a multimeter, pc based oscilloscope, frequency generator/counter.

mm210
mm210's picture

Hum, no output

Possibly something as simple as wire off input jack. Is there NO output from EITHER channel or just one.

ca7922303

hd130

Bought it off ebay to repair, had low distorted ouput on both channels. Messed with bowed up rectifier board. Had to resolder 55k resistor. Turned on blew fuse. New fuse, turned on to a loud hum not affected by any of the controls. Noticed a puff of smoke from power tube socket inside far right corner of chassis if looking at the back. Would appreciate any ideas. Have a multimeter, pc based oscilloscope, frequency generator/counter. Thanks.

ca7922303

hd130

No output both channels. Continuous loud hum, not affected by controls.

mm210
mm210's picture

Hd130

Sounds like you are going to have to go through the entire power section. Filter caps bad, tube took a dump, burned resistors on the sockets. You need to isolate the entire PS from the amp and check it. The smokes' the bad thing. Probably burned a resistor on the sockets. You should also isolate the power transformer and measure the voltages out of it and see if it's shorted anywhere. Mike.

ca7922303

hd130

I appreciate your response. Can I ask you to describe how to isolate the power transformer and measure the voltages out of it on this amp and how to isolate the power section and check it. I'm learning, but do have a multimeter, oscilloscope, frequency generator/counter, and can get more tools if needed. I'm also very aware of the shock hazard in these amps. I'm inexperienced and need all the advice I can get. I know it's alot to ask. Maybe some pictures of what I believe is the correct areas to work on and test would help the situation? Thanks for your help.

mm210
mm210's picture

PS

Well, I would start by locating every connection where the PS transformer goes and marking it. Take close up pictures if you can of where EVERY lead goes. Disconnect ALL leads from the PS transformer and measure the leads. You will get pretty low resistance readings but the thing to check is to see if ANY of the windings are shorted to the housing. THAT'S dead giveaway. Then, you will want to do the dangerous part. Hook some leads to the primary side and power up the transformer. You will want to identify each lead FIRST as to it's function. Which leads are what, in other words. The colors will be identified on the schem. Measure the voltages from the windings and compare them to the schem. As far as the caps, unless you have an electrolytic cap checker, the only think you are going to be able to do is check for shorts and cap value. Probably easier to just replace them. Like Steve said, that's a good place to start and it PROBABLY need them. If you're not comfortable doing this, STOP and have it done by a tech. You will have to check every component on the bias supply board, and all connections to and from the sockets. Also, check the sockets themselves for arcing and burnt resistors. Like I said, you are going to have to check EVERYTHING first and THEN get the results. Mike.

ca7922303

hd130

Thanks, i'll get started on it with your instructions shortly.

mm210
mm210's picture

Tubes

Also, don't overlook the fact that one of the NEW tubes could have taken a powder. Check them for shorts or substitute known good ones temporarily.

ca7922303

hd130

Yeah, I took all the tubes out and turned power on real quick and I get the same loud hum. Filter caps are brand new according to seller and I agree they look new.

mm210
mm210's picture

hd-130

OUCH-doesn't sound good. Try disconnecting all the Power Transformer leads BUT the ones connecting th epower to it and power it up and see if it still hums. Sounds like a massive short hum

mm210
mm210's picture

HUUMMMMM

You know, you never mentioned if the original owner had said it EVER worked after it had the NEW caps in. Maybe one in wrong/backwards, grounded, something. WHO did the caps and did it work AFTER they were done. What caused him to sell it without tubes? Did HE try to putthe caps in?

ca7922303

hd130 caps

I'm going to send you some pictures of the cap installation and see what you think. It's interesting that you mentioned that the caps could be in backwards. Looks like three(3) are facing one(1) way and one(1) is facing the other? Thanks for your help.

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