Panasonic top-loader VCR Issues

[vortalexfan]

A further update: The VCR will play EP recorded tapes fine (even though it doesn't have an EP mode option in the record speed switch, but I'm not sure what EP Mode would be the equivalent of in terms of SP, LP and SLP)

So either the tape speed detecting circuit inside the VCR is defective so as to not allow it to detect SP tapes, or another thing I thought of is that there's a drive belt on the topside of the VCR mechanism that goes from a pulley in the middle of the VCR Mech. to the playback idler and perhaps when I replaced that belt I put the wrong size belt on that pulley system and its causing the VCR to play at the wrong speed.

[Electronic M]

Originally Posted by vortalexfan

A further update: The VCR will play EP recorded tapes fine (even though it doesn't have an EP mode option in the record speed switch, but I'm not sure what EP Mode would be the equivalent of in terms of SP, LP and SLP)

So either the tape speed detecting circuit inside the VCR is defective so as to not allow it to detect SP tapes, or another thing I thought of is that there's a drive belt on the topside of the VCR mechanism that goes from a pulley in the middle of the VCR Mech. to the playback idler and perhaps when I replaced that belt I put the wrong size belt on that pulley system and its causing the VCR to play at the wrong speed.

EP and SLP are the same speed. Different brands used different names for that speed for God only knows why.

If it's tracking and playing perfectly at SLP/EP speed with an SLP/EP tape it's probably an electronic problem.

[vortalexfan]

Originally Posted by Electronic M

The playback speed is not sensed with a switch. It's detected from the linear control track of the tape by the electronic circuits that control tracking.

Usually the only user speed control is for recording mode only.

If it's that old it's probably worth trying to fix even if it's a complex electronic issue, but a service manual with schematic is going to be critical to success.

I do have a couple of Service Manuals for this VCR, but they are Sam's Photofacts that I downloaded from their website, so the schematics and what not are cut up into pieces.
Could a bad capacitor in the control board cause these issues? I know this unit uses the old Matsushita caps that were notorious for failing over time (the purple ones.)

So what part of the service manual would I look under to find that circuit, so I can start troubleshoot it?
Is there a specific name for that portion of the VCR Circuit? I'm asking because the Service Manuals I have go by the names of what Panasonic put on each of the boards (ie Servo Board, etc.)

[vortalexfan]

OK, so I tried out an LP recorded tape in the VCR and that also had some trouble playing in the VCR, so apparently whatever circuitry is involved with the VCR reading the speed of the tape on the control track on the tapes must control the SP and LP together and SLP is controlled separately from the SP and LP modes.
Although LP mode even though it wasn't playing at the right speed it was a much clearer picture (not as much sync issues) as the SP mode had, in SP Mode the picture had terrible sync problems (vertical and horizontal hold issues.)

Also how common was it for a VCR to have a failure of the speed sensing control system? I'm asking because this is the first VCR I've worked on that had this issue out of about 30+ VCRs I've worked on in my nearly 20 years of working on VCRs for people or for myself.

[redk9258]

I had a similar problem with a JVC HR-D470U. It was a high ESR cap in the circuit the reads the control track.

[vortalexfan]

Originally Posted by redk9258

I had a similar problem with a JVC HR-D470U. It was a high ESR cap in the circuit the reads the control track.

I realize a JVC VCR is Completely Different than a Panasonic/Matsushita VCR in how the Circuit Boards are labeled and layed out, but what board was it that was controlling the control track reading on the VCR? Was there a specific name for that circuitboard? I have the service data for my VCR but have no clue where to begin to look for that particular circuit on my VCR and it doesn't help matters any that the VCR has about 10+ circuitboards in it that all have a different name for them.

[Electronic M]

Haven't dug that deep into a deck that old with that issue but if I wanted to figure out which board(s) are involved I'd trace the control track wiring off the stationary head (which also contains the linear audio head on most decks) to a board and also trace the head drum and capstan motor wiring to a board. Those boards are likely involved. The older the VCR the more spread out the circuitry the first models may have read the control track on one board and passed it to 2 separate servo boards, the most recent ones did everything in the entire deck on one board. How muchand what was on one board in early decks sometimes has more to do with how compact they could build it by putting things certain places than logical placement.

If there's block diagrams in your service literature that may help you find things too.

[vortalexfan]

Originally Posted by Electronic M

Haven't dug that deep into a deck that old with that issue but if I wanted to figure out which board(s) are involved I'd trace the control track wiring off the stationary head (which also contains the linear audio head on most decks) to a board and also trace the head drum and capstan motor wiring to a board. Those boards are likely involved. The older the VCR the more spread out the circuitry the first models may have read the control track on one board and passed it to 2 separate servo boards, the most recent ones did everything in the entire deck on one board. How muchand what was on one board in early decks sometimes has more to do with how compact they could build it by putting things certain places than logical placement.

If there's block diagrams in your service literature that may help you find things too.

OK, so I figured out that the control track reading is controlled by 2 boards in this VCR, the Audio Board and the Servo Board, and sure enough when I took those boards out and looked them over they had several electrolytic caps that had spewed their guts (the green corrosion on the wires coming out of the bottom of the capacitors.)

So when I replaced all of the ones that were visibly defective, then I put the VCR back together and sure enough it started playing LP recorded tapes properly, but its still not playing SP tapes properly yet.
So I'm going to have to go back over those boards again and see if there were some capacitors that I missed that weren't as obvious looking and replace those, and I think it will be good to go.

[vortalexfan]

Well I double checked the boards I worked on earlier and I found several more bad caps I missed, so I replaced those as well, and in total I replaced between the audio board and the Servo Board a whopping 13 capacitors which all suffered from the green corrosion on the capacitor leads, but unfortunately instead of making it better, it made it worse, somehow.

it will still play LP and SLP (EP) tapes just fine but when you try and play the LP and SP tapes instead of getting a picture, I just get video noise (the same kind of noise you get if a tape's tracking is severely off) except that the tracking isn't off the audio is just fine (in LP Mode) and in SP mode it still won't switch to the correct speed.

And I'm not sure what else to look for because I've replaced all of the bad capacitors in the Servo Board and the Audio Board, and it only restored operation to LP Mode, SP Mode is still not functioning, unless there's something else I'm missing?

[Electronic M]

Double check that you didn't install any backwards or 10X or 1/10the value. Changing caps should not make it worse.

Transistors are not infallible. About the only deck that old I've done deep troubleshooting on was the first frontload Betamax (Zenith rebadge) that wouldn't run some key motors in play mode. One of the control transistors fried.

[vortalexfan]

Originally Posted by Electronic M

Double check that you didn't install any backwards or 10X or 1/10the value. Changing caps should not make it worse.

Transistors are not infallible. About the only deck that old I've done deep troubleshooting on was the first frontload Betamax (Zenith rebadge) that wouldn't run some key motors in play mode. One of the control transistors fried.

I definitely made sure to use the correct capacitance value, the voltage values were a tad higher than the originals on some of them because I didn't have any that were the exact voltage rating, but I figured that the voltage rating shouldn't affect it much as long as the capacitance value is the same.

As for the transistors I didn't think to check those, but the only time I've ever had issues with those was on some 1970s stereo receivers I've worked on where they popped and crackled out of one channel and it was one of the transistors in the amplifier section.

I will though double check to make sure I didn't accidentally install some capacitors backwards, because while they had the (+) and (-) clearly marked on the board, I might of accidentally stuck a capacitor in the wrong way thinking I had stuck it in the right way because I had been working on this thing for almost 8 hours straight without any breaks.

[vortalexfan]

I checked the Slow/Still Board and found some more bad caps.

Oddly enough all of the caps I replaced that were bad were 47 uF 16v electrolytics except for 2 of them, did Matsushita have trouble with the 47 uF 16v caps they made in the early 1980s?

[redk9258]

I don't think it's uncommon for small value electrolytic caps to fail after 30+ years! How are you checking the caps? For ESR?

[vortalexfan]

Originally Posted by redk9258

I don't think it's uncommon for small value electrolytic caps to fail after 30+ years! How are you checking the caps? For ESR?

I was using a combination of checking ESR with an older analog ESR Meter, and visual inspection, all the caps I replaced had green corrosion on their lead wires; which from what I had seen on repair videos by Shango066 and Jordan Pier, they said that was a common issue with certain types of Matsushita caps in older Panasonic radios, VCRs and TVs.

I was just merely pointing out that it was interesting that the majority of the capacitors that were replaced in this VCR were 47 uF 16v capacitors, but there were plenty of 10 uF, 1 uF, 22 uF, 100 uF and 220 uF caps in the unit that were still fine yet (still had low esr, and no green corrosion.)

The weird thing is that whenever I take a board out which involves me having to remove the many cable plugs attached to them to repair the board, and then plug them back in to check the VCR's functionality, I always end up having to take the board back out unplug the cables and reseat them again in order for the VCR to function as it did before I removed the board, and I'm not sure why that is the case.

[redk9258]

I hear you. I've been working on a couple of VCRs and 1 small PCB has 9(!) connectors! Two of which are ribbon cables that are supposed to be zero insertion force. I'm sure they are when they line up perfectly. I have the most difficult time getting these stupid things in! It must be old age. I can't open anything you buy in the store either! LOL