Philips Music Centre 22AH985

[TonyDuell]

I don't normally collect music centres as most of them were fairly poor quality. However, I think the Philips 22AH985 is an exception with a belt-drive turntable, magnetic cartridge tracking at 2g, output for MFB speakers, very modular layout inside, etc.

I bought one in a charity shop in Crawley about a week ago. Thankfully it will ust fit in one of those large blue IKEA bags, although getting it home by bus was still entertaining. Anyway it's now on my bench in bits. I have the service manual from 'up top' of course.

Inside there are quite a few PCBs :

Main amplifier and cartridge preamplifier

AM tuner/fuction switching

FM IF strip, the RF head and stereo decoder are plug-in daughterboards to this.

Tone control/preamp

Microphone input pre-amp (also carries the headphone socket)

The cassette unit is a separate module with a PCB on the bottom carrying the recording amplifier, Dolby noise reduction, DNL, and the playback amplifier are plug-in daughterboards. Obviously not a very high-end unit, 1 motor 2 heads, but probably not too terrible.

Faults so far :

Turntable belt broken, fortunately not turned to Evil Goo.
Stylus missing (GP400-II cartridge).
All 3 dial lamp bulbs burnt out.
Tuning drive slips sometimes.
Volume and tuning knobs missing. I've found some in my spares box that fit and which don't look too bad. Finding the orginals would be impossible I think.

The dial lamps are 12V 100mA (1.2W) tubular MES things. I think I can still get them. They run off AC which may be a problem if I tried to use LED replacements and I wonder if the light distibution pattern from those would be suitable anyway.


My plan is :

Clean out dust, etc.

Clean grease/gunge off the tuning drive.

Check/set the main amplifier quiescent current as per the manual. You replace each fuse with a 2 ohm resistor and tweak a preset for the correct voltage across it.

Reassemble the tuner/audio sections and test. Fit new dial lamp bulbs.

Strip, clean, lubricate the cassette unit. Maybe new belts if I can get them.

Test cassette operation.

Order turntable belt and stylus.

Dismantle, clean, lubricate the turntable unit. Reassemble and test.



Any suggestions/comments?

[TonyDuell]

I've made a start on it. Took everything out of the cabinet, it's very modular and the only wires I had to desolder were the ones on the FM aerial socket. Cleaned the parts,etc.

Refitted the mains transformer and tested the output voltages. Fine.

Stripped the tuning drive, cleaned off the hardened grease, put PTFE lubricant in the right places and put it back together. Now works quite well.

Temporarily fitted 2ohm resistors in place of the output stage fuses and tweaked the quiescent current presets for 160mV across them, as per the service manual.

Put the amplifier board along with the rest of the audio and radio boards back in the case, connected all the cables and powered up.

Radio, AM and FM seems fine. I can get some FM stations, in mono, with no aerial connected. I need to find a suitable aerial to give a good enough signal to test the stereo decoder. At least that board is easy to get to if there are problems.

BUT....

Both sides of the microphone input were dead. One side of the pickup preamplifier (annoying on the power amplifier PCB so it's painful to get to) was also dead.

OK, do the former first as it's easier to get to. Take out the control PCB and the microphone preamp PCB again. The DC voltages on the transistors were crazy although everything seemed to test fine. One red herring was that the supply rail was a little low, it comes from a voltage multiplier in the power supply section. Was that the fault, caused by the fault, or plain didn't matter. I spent some time checking components there. Nothing obviously wrong.

Back to the preamp board I then realised that without the transistors fitted, the bias network could be taken as a potential divider, and those I do understand. So desoldered the 2 transistors on one channel and found the voltages were not what I calculated. Found a 47uF electrolytic capacitor hung off it that was just leaky enough to muck things up. Replaced it along with the one for the other channel, refitted the transistors. Voltages now fine, and preamplifier works.

OK, to the pickup preamp circuit. Voltages in one channel were wildly incorrect. As a guess I suspect a similar electrolytic capacitor, this time 68uF. Get the amplifier board out, desolder that capacitor and the voltages return to normal. Replaced it temporarily with a 100uF part, along with the one for the other channel. I don't know what effect that will have on the frequency response, so I'll try to get some 68uF capacitors. At least I know that capacitor was the fault.

And that's where I've got to. Still got the more mechanical units -- the cassette deck and the turntable -- to work on.

[Edward Huggins]

You say that this is not "a very high end unit".
You are correct, but when fixed I think you will be pleasantly rewarded by its performance and sonic qualities. A well built and designed unit.

[TonyDuell]

From the design and construction I feel it's probably one of the better music centres. I would guess a magnetic pickup cartridge tracking at 2g is going to be better than a cheap ceramic cartridge tracking at 5g or more. And the fact that Philips added the socket for the (excellent) MFB speakers suggests it was intended to be 'above average'

It is well-made and easy to work on. I am certainly glad I bought it.

The latest update : Went to Cricklewood Electronics and got the 68uF capacitors and new dial lamp bulbs. I've fitted these and everything in the lower case seems to work. So just the cassette deck and turntable to do.

[TonyDuell]

Very minor update. Took the cassette deck mechanism apart, cleaned the bits (the pinch roller in particular was filthy!), put oil and grease in the right places and put it back together. Not done the tape unit housing yet, so I've not tested it but things seem to move correctly by hand.

I do like the magnetic slipping clutch for the play/record takeup spool drive.

[Sideband]

Originally Posted by TonyDuell

I do like the magnetic slipping clutch for the play/record takeup spool drive.

That was introduced into the better cassette mechanisms and later, I think became more or less a 'universal' replacement for the earlier friction types. Philips claimed that it reduced flutter and being frictionless it would seem logical. They also fell to bits.....!

[TonyDuell]

Now tested the cassette unit. Amazingly I got it all back together correctly first time. The only fault was that the autostop didn't work. I quickly found that the pause switch contacts which prevent the autostop from triggering when you pause the tape were always closed. Adjusting this fixed it.

So the cassette unit is now refitted.

The turntable needs work. A quick inspection shows problems with the pickup arm bearings, alas. I will carefully take things apart and work out what is needed.

[Edward Huggins]

If this is the arm with gimbal bearings, do make sure nothing falls out on to the floor which you may never find!

[TonyDuell]

I've removed the arm and carefully taken it apart. One of the bearings, 123 in the exploded diagram in the service manual, is missing (no, I didn't drop it!). The ends of the spindle 124 don't seem to have been designed to run in jewelled bearings, so I assume it's just a metal part. I will have a go at turning something to work, hopefully I can get a good enough fit for it to work smoothly.

[TonyDuell]

I've turned a brass replacement for the bearing and fitted it with a 1.5mm ball bearing to take the end thrust. Locked in place by an M1.4 screw into a hole I tapped in the gimbal housing. Probably better than the original glue! It seems to operate freely

Now sorting out the rest of the turntable unit.

[TonyDuell]

I completely stripped and cleaned the bit of the turntable unit. All seemed OK.

Then I reassembled the turntable, it runs properly. The belt shifter does so, the autostop trips when it should. So refitted it to the top case.

And it played a record perfectly. I've only tried it with headphones, which in this unit don't use the power amplifier, and it sounds very nice [There's a push-pull stage that feeds the headphone and MFB sockets, it also feeds the more powerful push-pull stage for the speaker outputs].

So, in went all the casing screws, on went the knobs, and essentially it's finished. There are 2 more stages to this project, the mundane one of finding a place for it in my living room won't be discussed here, but sorting out the speakers might be. I have a pair of Philips 22RH541 boxes that I plan on using with it. I'll start another thread when I work on those.

[bobbyball]

Quite a "high end" model for Philips at least. It's probably full of those blue Philips electrolytic capacitors that have lasted for so long but have now by and large come to the end of the road. I have lots of Philips things full of them and they are all going now...

[TonyDuell]

I had to replace the 'blue electrolytics' in the microphone and record cartridge preamp circuits, they were leaky enough to upset the DC conditions. I'll replace others as/when they cause problems.

I do think it's a fairly high-end unit. It's a lot better than most music centres (and way above the tat that is sold as a record player these days).