my old and loved HH micro 30 is sickly

[semaphoresteve]

Hi I wonder if anybody can help me with a problem with my HH micro 30. I have been using valve amps for sometime now but I've had this amp for 30 years now and it's got a bit of sentimental value if little actual value. My son was using it until recently when he brought it to me saying it wasn't working. I had a quick look and noticed the power smoothing caps looked dodgy and the two small fuses had blown. I replaced the power caps with the nearest equivalent (63v instead of 45v) and one of the rectifier diodes which I thought was giving an odd reading. New fuses and the amp came back to life. I thought that the volume was a bit lower than I remembered so I replaced some of the other caps. The amp seemed ok and I used it for a couple of gigs to give it a bit of a road test. However last time I came to use it I could hardly get any volume out of it at all. Cleaned all of the pots and retested some of my new joints but can't find anything obvious. The new caps were a big bigger so are a bit of a squeeze.

I'm really not very experienced with electronics, although I can follow instructions.

Another symptom is that the amp makes a loud pop when removing the jack from either the hi or low input

Any thoughts please

[joecool85]

I'd clean up or replace the input jacks and see if that helps, good change they are all cruddy and causing issue.

[semaphoresteve]

Thanks I'll try that and report back.

[J M Fahey]

Look at the PCB, both sides, with a loupe and under good light, around the input jack soldering.
You may have crached solder or tracks.
If in doubt, retouch solder pads with a bit of solder and a clean tip soldering iron.
If possible, replace the worn tired jack with a new one.

[semaphoresteve]

Hi all, I replaced both input sockets and the wiring to the pcb. No change though I'm afraid. The really unusual thing is how loud the noise is when you plug in or pull out a jack. The amplifier seems to be working but something definitely wrong on the input side. The amp has a Volume (gain) and a master volume. Is there anything in the gain circuit that could have failed or should I just keep resoldering connections on the pcb.

steve

[J M Fahey]

No schematics available for these old warriors.
Take 2 sharp clean well illuminated closeup pictures of the PCB showing the input jack and the closest IC or transistor (they might either go straight to an IC or use a FET input), one showing the solder side and another the component side.
Both at approximately the same distance and angle, so by seeing both at the same time I may follow how parts are interconnected.
What guys do to copy pedals and such.
Then I might suggest something.

[semaphoresteve]

It's amazing that people are willing to spend time to help keeping these old amps going. In particular how patient and generous people who know more about these things than i do.
Here are some more pics

[semaphoresteve]

Hope these help...to save you a bit of time decoding. O 1  O 2 O 3 on the pcb is where the inputs connect to the board. 1 is the grey wire 2 is the ground and 3 is the blue wire. 3 connects to R10 and 1 connects to one leg of what I think is a transistor. The soldered side looks awful I know, but the old capacitors had the legs soldered along the tracks and were difficult to remove without damage. I've checked these connections and they seem fine. I may have connected something up incorrectly but I don't think so.

Thanks for your help so far

steve

[phatt]

Just remember there is (what looks like) a headphone socket on the front.

Those (like FX loop sockets) can steadily go intermittent/ open circuit over time.

Most HP sockets will have a break switch to the speaker terminals so that it kills signal to speaker upon insertion of H/phone.
Make sure that switch is connecting through to the speaker.
If you live in a high humidity climate they can give all sorts of problems.
Phil

[Roly]

The soldering on the input sockets looks none to brilliant.

If you plug a pair of headphones into the headphone socket is it still weak, or do you get a good level in the 'phones?

[semaphoresteve]

It's the same through the headphone socket. The new inputs were just rigged quickly to test everyone's theory that the inputs were faulty/dirty.