WHSmith RC8321: (Morphy Richards RC220) Radio Cassette Player

Hi Paul, 

Welcome to the forum. ?

It might help if you stated what the make and model is of the radio cassette you're trying to repair. Without knowing this, its a huge guessing game for any member attempting to comment or provide you with assistance.

Posted by: Imposter

Stil no joy, but when I was replacing  cap i did hear a crackle in my earpiece which i leave in whist trying to fix it.

Paul

Welcome.

Do you mean by that comment that you have the cassette powered while you are replacing components? That is a complete NO NO!!! You NEVER have any item powered while replacing components. Without going into details, critical bias (circuit voltages) can be disrupted which can cause instant (and I mean instant) destruction of chips and transistors. Voltage checks should be largely all you need to do to check if the output chip is actually working. Suspect components must be removed and if necessary replaced with the unit off.

Lets have more details as Chris has already said.

Hi Guys

Thanks for your responses and welcoming me to the forum

The unit is an RC8321 badged as WHSmith, I had one when i was a kid but i am sure it was labled as something else.

@sideband  no it wasnt powered on but i was switching it on to test every time i changed a cap, i started with the caps around the amp chip 1st, so they will have some charge in them when replacing the next one on.

Thanks again for taking the time to look

Hi Paul

Posted by Imposter

Firstly, please excuse my complete ignorance. I am working on a large Project that is going to involve some electronic work and I thought that I should learn something first.

I cannot find any broken lines or dry solder joints or damaged caps so i have replaced all the caps anyway bar 3 which were 47mf 10v which CPC didnt have in stock.

as you openly admit you're new to this hobby perhaps you won't mind me recommending something quite important to remember going forward from here. When faced with a faulty piece of electronic equipment, cap changing en masse is not the panacea to fix all faulty equipment as you have obviously found out. No worries, you're not the first and I doubt you'll be the last to do so.

On very old equipment with dubious paper/waxy capacitors and ancient electrolytics, its a fair game approach to take precautions and swap them out prior to power up, though some prefer to not even do that. However in the case of your Radio/Cassette being a fairly modern piece, it would be highly unlikely you would need to change them all.

The basics you should be aiming for and where to start, is with your power rails. Establish what is expected, establish what you have and can you follow it through the circuit. On the way you're looking for any anomalies such as o/c, s/c , leakage and high esr on electros and of course out of tolerance components, all in a logical and methodical fault finding manner. Taking the former approach will lead to frustration when it yields minimal results and saps confidence. Taking the latter approach will teach you far more and set you up with confidence for when you tackle your "Large project".

All this needs on your part is a multimeter and in the case of a new starter, a circuit diagram is mandatory as you have no experience to fall back upon.

As this radio is a mains(240VAC)/battery(6VDC 4x HP2) portable I suggest you do all your power tests using batteries, that way no danger of you electrocuting yourself when taking live voltage readings.

The W.H. Smith RC8321 must be another make just badged as W.H. Smith maybe a Sanyo/Saisho/Goldstar etc. If Vrat members can help identify the actual model, I may be able to source the service data (circuit diagram) from my library which will make life oh so much easier for you.

Thanks Crusty

I Appreciate the advice, I have been using a dc adapter with tested correct voltage instead of mains to saving the over enjoyment of and eventual cooking of my internal organs ? 

A curcuit diagram would be most helpful indeed, i just wish i could remeber the brand of the original i had.

As you pointed out i am unable to track back as i dont know what i should be getting, i am getting power to the tape/radio switch, which get 6v and when switched over to radio outputs 6v but the switch has about another 6 pins on it of which i dont know what should be happening. i have tried spraying ipa through the switch to clean any dedbris of which their was some. but no voltage changes.

So if anyone knows who made it or a diagram it would be extremly helpful.

I cant seem to attach a pdf of the amp chip, as it would have been helpful if someone could tell be if i should get voltage out of leg 8 so here is a piccy

Thanks again

I have used the upload service to upload the data sheet on the TA7628 chip, it’s not the p version though.

Radio museum have a circuit for a Grundig radio cassette that uses a TA7628 chip with voltages. It may possibly help if a correct circuit cannot be found and using the data sheet as well.

RM allow 3 downloads a day, each page of the manual is one download but only one page is probably required.

https://www.radiomuseum.org/r/grundig_rr225rr_22.html

Note RM do not allow posting the material to other web sites.

Through some thorough brain bending research, I've ascertained your W.H. Smith RC8321 is a clone of the Morphy Richards, the cabinet just slightly varies in style. The Morphy Richards RC220 uses the exact same chassis and chip (see below) that your W.H.Smith RC8321 uses. The Morphy Richards model RC222 is the clock radio edition but again uses the same chassis but with additional clock circuitry.

Thankfully there is data for the Morphy Richards so you're in luck, I'm in the process of sorting out the circuit for you.

p.s
The player dates from 1984

p.p.s
I've added additional tags to the first post, this so it reflects the new identity information to make it easier for folks in the future should a similar request crop up. Also edited the thread title.

The service data for this Radio cassette now resides in the data library. ?

The data can be found under the "Radio" category and is listed in two sections, one for Morphy Richards RC220/RC222 and one for WHSmith RC8321.

As Paul has not yet earned access to the data library, as a good will gesture I have e-mailed him a copy. 

Looking at the photos of the PCB, pin 13 appears to be unsoldered, this is the preamp output for the tape.

Wow, thank you all very much indeed, what a wonderfull bunch you are, I did try to edit the Title previously but couldn't.

The Grudig one also looks to similar , so thats also great.

Just seen the email with the attached PDF.

Looks like today is a win. 

Thanks to you all

Wowzer, Ermmmmmmmm.

So is there a diffinitive guide on how to read and understand the wiring diagram, lol, or possibly ram all required info straight in to my mind like johnny mnemonic.

What do you have a problem with, something specific or is were do you begin?

I feel more confused now looking at the diagram than before. lol

Yeah a place to start would be good, I know I have no sound so i thought it would be good idea to start at the amp and try and find which leg/legs is not getting the correct voltage and then work from their, but after looking at the diagram............. ? ?  No Idea

Download the specification sheet for the TA7628p IC, it gives a test circuit and an application circuit. It will not be exactly the same as the radio you have but near enough to work out what does what and if the audio amplifier section is working correctly.

Did you check that poor soldered joint on the IC?

HI Frank, yeah resoldered that one, but i hadn't spotted it until you pointed it out, so thanks, no joy - i could only see it under the magnifier. i have no idea how you spotted it. hehe.

I have the amp pdf but being so new i dont get what the test circuit is asking tbh, I know i am way out of my league, i do have a technical background but not in electronics so any pointers on how to read this.

Many thanks again

Paul

Pin 10 is VCC and pin 7 chassis. Expect about 6 volts on pin 10 with respect to pin 7. An audio signal fed into pin 5 should give an output in the speaker, looking at the specification the preamp gives about 0.5v audio, doesn’t say if P to P, peak or RMS., so start with  a low level signal.

When you say "with respect to pin 7" do you mean 7 being ground, can i use any ground? or does it have to be specific leg 7? either way i am get correct voltage.

regarding pin5 how do i test that? play an audio signal in to that pin? if so i can do thst but if i put the positive from my out put on 5 where do i put the negative?

This help is awesome by the way

Pin 7 should be ground so worth checking, if it is at ground(battery negative) then use that.

I say with respect because if pin 7 is floating then there will not be VCC across Pin 10 and Pin 7 and using ground instead of Pin 7 would still show 6 volts.

Hope that makes sense, not at my best explain these type of things.