View Full Version : Model 2220 problems


Jailtime
10-12-2009, 09:15 PM
I dug the 2220 out of storage to check it out prior to its restoration. It has a nasty hum in both channels. The left channel has lower output than the right. The controls are well Deoxited and Faderlubed. I'm suspecting the filter cap and the coupling caps. Maybe something in the preamp for the lower left channel output. Should I proceed with a recap? Or are there problems stemming from a bad transistor?

avionic
10-13-2009, 06:15 AM
T-shoot the Hum first.Its probably the PS filter caps.Measure the AC ripple across the big filter caps and the usual visual check for bulging or signs of leakage.

jblmar
10-13-2009, 01:05 PM
Jailtime,
Is there hum with the volume turned full down?

Jailtime
10-13-2009, 07:39 PM
Jailtime,
Is there hum with the volume turned full down?

Yep. The hum doesn't get noticeably louder when the volume knob is turned up either. It will get slightly louder at about 12 o'clock.

ecluser
10-14-2009, 01:09 PM
If the receiver was in good order prior to storage, I doubt the problem is related to transistors. Dried caps probably.

There is a 35V regulator on the P800 board. This regulator feeds the tone control board, which is after the volume and balance controls. See if you have hum on the 35V output, pin J808 on the P800 board, or pin J510 on the P500 board.

What test equipment do you have?

Jailtime
10-14-2009, 01:21 PM
What test equipment do you have?

None. :no: Wish my cassette deck was in operating order, I'd use it. I have your handy thread bookmarked. :yes: Well, I do have a DMM, but I don't consider that test equipment.

ecluser
10-14-2009, 04:37 PM
I will make you this suggestion. Disconnect the two wires at J701 and J702, on the power amplifier board (P700). They are the input wires to the power amp section.

Measure the AC voltage with your DMM (yes, it is a test equipment) at pin J710. Without audio signal, the AC voltage at J710 should be very low.

If you still hear hum, replace C703 and C704. They are the power supply filter caps for the input stage on the power amp. Replace by the largest (uF) cap you can fit there, 50V is enough.

If you don't hear hum, the main filter cap (C006, 4700uF/63V) is good enough and doesn't need to be replaced.

If there is hum with new caps at C703 and C704, check the diodes in the main rectifier bridges. It is best to remove the bridge rectifier for testing the diodes. If you don't remove the bridge, you will be fooled by the presence of the main filter cap and the secondary winding of the transformer.