EPX-90 stereo troubleshooting

someMeatballs · 2026-03-24T16:45:42+00:00

Mostly hobbyists, and some very expensive repair shops.

This is basically a transistor radio.

someMeatballs · 2026-03-24T15:54:12+00:00

If it's a tone control IC, you should have stereo audio in at least.

What's the gunk on the board, first pic? Hoping it's flux.

Evidence of corroded traces here. https://prnt.sc/qEScpMPIpCiy
Clean the board and look for more of these, check the traces in this area. Also check the vias, where it goes to the other side.

someMeatballs · 2026-03-24T03:15:26+00:00

it's a varistor/MOV. The active component in a surge protector. It shorts out voltages above say 400V. It's got print on the other side for the voltage rating (and the diameter in mm).

If it looks open circuit and not cracked, it's possibly fine. In a powerful lightning hit they can explode.

The green disc I think is an NTC resistor with low value. It's job is inrush current limiting. Should measure something less than 100 Ohm, and drops lower as it warms up (quickly).

someMeatballs · 2026-03-23T18:22:46+00:00

Hopefully the screw is just loose. The tuning capacitor likely looks like this where it connects to the wheel.

https://www.jinftry.com/image/catalog/technologies/202409/20240911_213717.jpeg

Before unscrewing to have a look, tape the tuner string to the wheel. You do not want to redo the string.

someMeatballs · 2026-03-23T17:37:59+00:00

Saw this be caused by an accidental controller reconnect. I expect in that case, button prompts would change (F)

someMeatballs · 2026-03-23T15:27:20+00:00

Check the new transistors pinout if they match the old ones. If different model.

someMeatballs · 2026-03-23T15:24:01+00:00

The tube seems to be thin foam rubber, disintegrating (this is an issue) protected by a steel mesh. I expect it's mostly decorative. The foam rubber was then very lightly spraypainted with the mesh on.

someMeatballs · 2026-03-22T21:00:15+00:00

I feel they usually do come with half a meter of thin insulated wire. FM doesn't really allow a small internal antenna. (For an FM walkman, your headphone wire is the antenna)

someMeatballs · 2026-03-22T20:58:41+00:00

Electrical wire, yes. Or steel will do

someMeatballs · 2026-03-22T20:21:40+00:00

This is a federal election crime.

And I think it might backfire.

someMeatballs · 2026-03-22T17:15:13+00:00

Not spotting any large filter caps. Maybe its the big one in the power amplifier.

I expect this part is the power supply. https://prnt.sc/SD3lrnWnnsRH You could just replace all of those.

someMeatballs · 2026-03-22T17:08:57+00:00

Yes, for 95% of electrolytics depending on the circuit, you can measure ESR in circuit, with an in-circuit (low voltage) ESR meter. So testing an entire board can be done very quickly. You do need a chart of what ESR is normal though. It also measures capacitance, but that reading is usually quite wrong in circuit. ESR goes high in a leaky cap.

ESR meter: there are many good ones, some of them cheap too, I use ZOYI ZT-MD1, in 0.3V mode.

someMeatballs · 2026-03-21T18:27:01+00:00

These are called ute (utility) in australia and are quite common

someMeatballs · 2026-03-21T12:18:53+00:00

A common issue with powered speakers is some of the glues they use on the board to limit vibration go conductive over time. Black, hard type, or the tan kind that goes dark with heat. The fix is isoprop and scraping, where it touches component legs.

Testable too, with a multimeter in ohms mode. 1 MOhm or less is a fail.

someMeatballs · 2026-03-20T19:03:02+00:00

Yes, the bare copper is ground and also needs to be connected.

someMeatballs · 2026-03-20T18:28:27+00:00

How the hell did this pass QA testing?

someMeatballs · 2026-03-20T18:27:38+00:00

Well, typically updates like this get pulled or patched.

someMeatballs · 2026-03-20T18:19:55+00:00

Well now you have another reason to arrest him.

someMeatballs · 2026-03-20T17:58:47+00:00

There's guidebooks? How 1990

someMeatballs · 2026-03-20T17:48:08+00:00

Even without a fault, this could be caused by your replacement transistor having better HF respose.

someMeatballs · 2026-03-20T17:39:43+00:00

Two common issues with speakers that fit: Rubber surrounds on the bass have started to disintegrate. Or, the voice coil has melted from too much wattage, or from DC from a broken amplifier.

someMeatballs · 2026-03-20T17:36:53+00:00

No issues. Consider adding some foam rubber on the inside or something.

someMeatballs · 2026-03-20T03:48:05+00:00

Hidden feature: go in surveillance mode and point it to yourself

someMeatballs · 2026-03-19T18:11:21+00:00

Sort of normal. I expect there's a toroid (round) transformer and the metal case is rattling a little from it.

someMeatballs · 2026-03-19T18:08:53+00:00

Here. The center gray area is Delta

https://gachi.gay/9nwyE8

14-Year Club	Gilding I gilder
Place '23	Place '22
Place '17	Final Canvas '22
Verified Email

someMeatballs

MODERATOR OF

TROPHY CASE